In general, test cabling and test connections must all be designed to minimise resistance (R), capacitance (C), and inductance (L) between the device under test (DUT) and the used source-measure unit (SMU) explains the applications engineering team at Keithley Instruments

To minimise resistance, use heavy gauge wire wherever possible, and definitely within the test fixture itself. The gauge required will depend on the level of current being carried; for example, for cabling that must carry 40A, a 12 gauge cable is probably necessary. For guidance on choosing cabling for higher current levels, refer to construction industry wire gauge tables, such as the one available at: www.powerstream.com/Wire_Size.htm. Check the ‘Maximum amps for chassis wiring" column to find the wire gauge needed to carry the level of current involved.

Low-resistance cabling is critical to preventing instrument damage. Choose cables with resistances of less than 30 milliohms/meter or lower for 10A pulses. Keep cable lengths as short as possible and always use low-inductance cables (such as twisted-pair or low-impedance coax types), heavy gauge cable in order to limit the voltage drop across the leads. Ensure the voltage drop won't be excessive by checking the SMU's Voltage Output Headroom spec. For example, if you were using a Keithley Model 2602A (pictured above) SMU to output 20V, the test leads should have no more than 3V of voltage drop across them to avoid inaccurate results or instrument damage. It is specified for a maximum voltage of 3V between the HI and SENSE HI terminals and a maximum voltage of 3V between LO and SENSE LO. 

Although many believe guarding can minimise the effects of cable charging, this is typically more of a concern for high voltage testing than for high current testing. Four-wire Kelvin connections must be kept as close to the DUT as possible; every millimetre makes a difference.

Also, it should be noted 0voltage readback should be done with the SMU that's forcing voltage, because the current-sourcing SMU's voltage readings will all vary quite a bit due to the connections, and will differ from what is actually seen at the DUT.

The jacks used on the test fixture should be of known high quality. For example, some red jacks use high amounts of ferrous content to produce the red colouring, which can lead to unacceptably high levels of leakage due to conduction. The resistance between the plugs to the case should be as high as possible and in all cases >1010 ohms.

Many published test setups recommend adding a resistor between the SMU and the device's gate when testing a FET or IGBT. When pulsing large amounts of current through these kinds of devices, they tend to oscillate. Inserting a resistor on the gate will dampen these oscillations, thereby stabilising the measurements; because the gate does not draw much current, the resistor does not cause a significant voltage drop.

If voltages in excess of 40V will be used during the test sequence, the test fixture and SMUs must have the proper interlock installed and be operated in accordance with normal safety procedures.

Many electrical test systems or instruments are capable of measuring or sourcing hazardous voltage and power levels. It's also possible, under single fault conditions (e.g., a programming error or an instrument failure), to output hazardous levels even when the system indicates no hazard is present. These high levels make it essential to protect operators from any of these hazards at all times. Protection methods include:
- Verify the operation of the test setup carefully before it is put into service.
- Design test fixtures to prevent operator contact with any hazardous circuit.
- Make sure the device under test is fully enclosed to protect the operator from any flying debris.
- Double insulate all electrical connections that an operator could touch. Double insulation ensures the operator is still protected, even if one insulation layer fails.
- Use high reliability, fail-safe interlock switches to disconnect power sources when a test fixture cover is opened.
- Where possible, use automated handlers so operators do not require access to the inside of the test fixture or have a need to open guards.
- Provide proper training to all users of the system so they understand all potential hazards and know how to protect themselves from injury. It's the responsibility of the test system designers, integrators, and installer to make sure operator and maintenance personnel protection is in place and effective.

The need to protect IT equipment from the effects of power transients, as well as to provide assured operation during power outages is evidenced by the steady growth in sales of uninterruptible power supplies (UPS) up to the global downturn of 2008 - 9 (IMS Research). As markets start to bounce back post global downturn, the sales of UPS equipment has started to recover and are predicted to return to real growth during the coming 2 - 3 years. Michael Adams, global vice president for data and IT at AEG Power Solutions, explains

With IT central to the successful operations of most modern organisations, the UPS has a central position in the critical physical infrastructure which supports servers, storage and communications equipment, and which ensures continuity of services during all local mains conditions.

Recently, escalating energy costs and increasing concern about the carbon footprint of organisational power requirements, has driven the need to consider alternative back-up technologies and evaluate their effectiveness to ensure ‘business as usual' has become pressing.

Pressure on IT and facility managers to utilise green technologies, especially in Western Europe, continues to grow. In addition to the environmental benefits associated with lower carbon footprint, green technologies bring with them lower operating expenses by virtue of their more efficient operation and ability to deliver ‘more with less', i.e., more compute cycles from less energy.

As a discipline, energy storage technology has acquired new levels of prominence as methods are sought to overcome intermittency issues associated with solar and wind power generation. Smart grid concepts are being tested which are likely to promote an increasing trend towards distributed power generation combining traditional power sources with renewable or green power sources.

The eco-friendly storage industry is currently small, but solutions are either on the verge of commercialisation, or are starting to experience mainstream uptake. But another wrinkle is posed by the fact the choice of energy storage solutions is highly application-specific, as it varies as per application and requirement of the end-user.

Supercapacitors, or SuperCaps, are not a new concept and their effects were first noted in the late 1950s. Consequently, the technology is well established; has experienced significant advances over the last 10 to 15 years and has also seen recent reductions in cost. At the moment, supercapacitors have been successfully adopted in three different sectors; transportation, industrial and consumer electronics.

Why should we consider SuperCaps in UPS applications?
SuperCaps core technology is environmentally friendly and offers a high power density (4000W/kg). It has low internal resistance (ESR) and can operate in a wide temperature range which is very useful for data centres. The systems also offer a low total cost of ownership (TCO) and are capable of over one million cycles and offer instant recharging.

There is no doubt there have been significant developments with battery technology over the years, but despite all these advances, they all suffer from the same basic problem in that they utilise a chemical reaction. This means they suffer from a limited life, and can only operate in a limited temperature range.

In addition, traditional batteries that experience constant high demands for current, have a shortened operational lifespan. Therefore in order to ensure reliability and long lasting cover, facility managers are forced to deal with higher maintenance costs.

It is well known batteries die after a period of time, and need replacing on average, every two, five or seven years. Any technology that can offer a longer lifetime, so that users do not have to spend their precious budget repeatedly on replacement batteries, will prove to be a big incentive.

The SuperCap UPS provides a useful alternative solution in this context as it is ideally suited to provide a short-term ‘bridge' power until standby power generation equipment kicks in. As the SuperCap industry continues to experience a lot of R&D and maturation, SuperCap UPS systems are now becoming highly competitive with, and in many cases superior to, older bridge technologies.

TCO Considerations
Offering a wide temperature range, long life, and flexible voltage range, SuperCaps provide an extremely reliable solution for bridge power.

The very high cycle life of a SuperCaps UPS means unlike lead acid batteries, there will likely be little or no need for constant replacement. The facility to repeatedly charge and discharge for up to a million cycles without disintegrating, means the lifetime cost of the SuperCap is expected to break even with lead acid batteries.

Longevity is helped by the fact their high power density results in reduced strain on the battery in times of need. Another major consideration is the fact the SuperCap also has the ability to recharge instantaneously, in a few seconds. This is really useful in data centres, to help cut power costs associated with keeping batteries charged.

Another important factor is the ability of SuperCaps to offer versatile functioning in a wide temperature range, dramatically reducing cooling costs. This is because the function of a SuperCap does not require a chemical reaction, and therefore, does not involve an optimal temperature range for best performance or longevity.

It has been estimated the supercap can be used from -40°C to +70°C, without degradation in its performance characteristics. This is in stark contrast to the lead-acid battery, which when used in industrial applications, almost always requires a mechanically cooled environment.

Pros and Cons
The SuperCap is green in two ways. Firstly, it reduces waste because it has a very high cycle life, and therefore decreases disposal issues. Secondly, the materials and substances used in the SuperCap UPS are toxin free and biodegradable, e.g., nano carbon particles are commonly used. They can operate in a wide temperature range without any degradation of performance characteristics, and it also has the ability to recharge instantaneously in a few seconds.

SuperCaps are ideal energy storage devices for fast and short-term peak power delivery, which is why they are so suited for UPS systems. They are also more efficient than conventional batteries as they do not release any thermal heat during discharge, and various figures have shown that they operate at around 80% - 95% efficiency in most applications.
SuperCaps also take up much less room compared to lead-acid batteries, and indeed weigh less as well, which can be an important factor in certain situations or locations. The table below contrasts the pros and cons of SuperCaps with traditional UPS technology.

There is no doubt the industrial market needs an energy storage solution that is both reliable, and can offer a quality service. SuperCaps offer high power density, cycle life, and thermal susceptibility, and the increasing adoption of renewable energy expands the possibilities of using SuperCap-based technology.

Frost and Sullivan points out the total world ultracapacitor (SuperCap) market had generated revenues of $113.1m (£75m) in 2008 and is likely to reach $381.9 (£250m) by 2015. It feels this market has witnessed growth (despite the economic situation) due to the great interest in propelling alternative energy storage mechanisms by governments. Indeed, Europe has given the highest priority to any environmentally friendly technology and has a proud tradition of being one of the first global markets to accept new technology and consider its applicability in various solutions.

The high price of oil, coupled with high electricity costs, the need for devices that can reduce the power burden of a data centre represents a significant opportunity. The increasing use of supercap technology within the transportation industry will also serve to spur new developments and help drive down the initial cost of ownership.

Electrical contractors can not and must not take the recycling of fluorescent bulbs lightly says Terry Adby

How many electrical contractors does it take to change a light bulb? It doesn't really matter, because, with the double focus nowadays on health and safety and sustainability, the real question should be: "Do they know what's being done with the old one?"

As efficient electrical waste disposal gets both more complex and more necessary - for financial, operational and legal reasons - those involved in electrical engineering and building services would be unwise not to pay heed to the answer, a fact that one recent prosecution has shed some revealing light on.

The sustainability lobby's continued success in promoting the balancing of successful business with effective environmental protection (not to mention the wellbeing of the immediate workforce) has ever greater ramifications for the industries responsible for creating and managing the built environment.

Sustainability, above all, is an area where electrical contracting, now worth some £8bn per year, has a key role to play, with the opportunity to propose ‘low or no CO2' options. But to play its role successfully the industry must also pay close attention to the matter of the waste the ‘alternative' option creates, and how it is disposed of.  Developments such as the WEEE regulations (Waste Electrical and Electronic Equipment Directive) impose legal obligations on contractors over the management of ‘waste streams' onsite, and in their subsequent disposal. It aims to "improve the environmental performance of businesses that manufacture, supply, use, recycle and recover electrical and electronic equipment" and has put the practical management of sustainability centre stage. For the electrical contractor its implications are unavoidable.

Energy efficient light bulbs (‘end-of-life gas discharge lamps') are covered by the WEEE regulations and present a particular challenge, because they contain mercury and are classified as ‘hazardous waste'. When these lamps are recycled the potential release of mercury into the air at the lamp crushing stage is a threat to both the wider environment and those in the vicinity if the right protective equipment is not in place. Each time a fluorescent bulb is crushed or broken, mercury vapour is released. If the gas is not effectively captured, that vapour will find its way into the atmosphere, the staff and others in the area.

The challenges of lamp recycling made headlines earlier this year when a Glasgow-registered company, Electrical Waste Recycling Group, and one of its directors, were fined a total of £145,000 plus costs after recycling processes being used for gas discharge lamps exposed workers to toxic fumes for a period of up to ten months.

If an electrical contractor is going to propose the likes of optimal lighting configurations or energy efficient lighting units, and if they are tempted to employ energy efficiency as a sales tool, they should be confident that the principles and practice that underpin sustainability and safety are being applied all the way through the supply chain, including what happens to the waste.

Bulb crushing on an industrial scale is a serious undertaking that comes with huge levels of environmental responsibility. Nevertheless, electrical contractors may face the prospect, perhaps even at the tendering stage, of client pressure to commit to deliver such a service. Contractors need to be completely confident of the ability of the suppliers they choose to meet their commitments. They also need to know what is being done in their name further down the supply chain.

In the case of Electrical Waste Recycling Group, it was the failure to ensure the safety of the lamp crushing phase of the recycling process at its Huddersfield plant that let down the company, their workforce and the local environment. EWRG, which runs easyWEEE, WERCS (Waste Electrical Recycling Compliance Scheme) and other recycling schemes, were contracted to handle commercial waste for several Local Authorities, which included light bulbs. While none of these clients were in any way implicated along with their supplier, the judgment in the case suggests others in the chain - such as electrical contractors - could be more vulnerable. It has already been indicated in court that putting a service out to a third party does not absolve an organisation of key responsibilities and, in respect of health & safety, the HSE - which brought the successful prosecution in the EWRG case - has said that "The client must ensure whoever carries out the work is able to do so in a way that controls risks." As this case suggests, sustainability and health and safety responsibilities often go hand in hand.

Some of the details of the EWRG judgment highlight the type of issues any business, including electrical contracting businesses, should take into account to ensure they and their suppliers comply with statutory requirements when dealing with waste. The promises of suppliers, the judge made clear, are no defence in the eyes of the law. They must be effectively monitored.

One of the judge's major criticisms was the lack of an effective risk assessment process at the EWRG recycling centre, not least because issues highlighted - such as excessively high mercury levels for no apparent reason - could have been rectified much earlier had risk assessment been in place. It is, in any case, a legal requirement for an employer in discharging their obligations to keep workers and the public safe as far as "reasonably practicable".

The HSE recommends five steps for effective risk assessment: identification of hazards; establishing who might be harmed and how; evaluation of risk and deciding on precautions; recording and implementing findings and regular review. Suppliers in a business as hazardous and regulated as lamp recycling should certainly be implementing all five. Those employing them to do the work should be equally concerned that they are.

The judge in the EWRG case also stressed the need for competent staff to be involved in the process monitoring, who understand the regulations and have the knowledge and experience to spot a breach or issue. Most successful organisations, he said, have employees who understand why risk assessment and vigilance is important for the company, staff and other groups with an interest, such as the local community. 

However, all responsibility cannot be delegated to one individual or team, he added. Senior managers need to put themselves in the position of being able to interpret and understand the implications of the results of any monitoring which is undertaken.  If they do not understand the implications of results, they cannot just ignore them. In the case of a prosecution it will be the senior managers and directors who will be held responsible. It is clear, above all, when things go awry, buck passing between organisations or individuals is not an option.

EWRG paid a heavy price because it did not read nor heed the warning signs. Those looking for lessons from its prosecution certainly should however. The safe recycling of energy efficient lamps may represent a beacon for a better future but, viewed from both an environmental or health and safety perspective, the message for electrical contractors is clear: the responsibility for a safe and sustainable approach to lighting may not end with the life of the low-energy bulb.

Mike Frain of Electrical Safety UK, examines live working on low voltage systems in industrial and commercial facilities, detailing a methodical process for identifying the risks associated with live working and the methods for controlling them

From my experience, I believe Regulation 14 from the Electricity at Work Regulations 1989, referring to live working, is often misunderstood and sometimes overlooked. The duty holder is asked to apply a rigorous test of reasonableness in allowing live work to proceed in the first place, and to prevent injury by taking suitable precautions. It must be stressed that Regulation 14 requirements are ‘absolute' which means it must be met regardless of cost or any other consideration. With this in mind it makes it very important that any live operation must be subject to a suitable and sufficient risk assessment.

Regulation 14 - Work on or near live conductors
A person shall not be engaged in any work activity on or so near any live conductor (other than one suitably covered with insulating material so as to prevent danger) that danger may arise unless
(a) it is unreasonable in all circumstances for it to be dead; and
(b) it is reasonable in all circumstances for him to be at work on or near it while it is live; and
(c) suitable precautions (including where necessary the provision of suitable protective equipment) are taken to prevent injury.
Before we move on, let me highlight a few of the important words from Regulation 14.
Near. This word debunks the myth live working only means those activities that require the manipulation or the removal/replacement of live conductors and components. Live work can also mean live testing and testing for dead. It can also mean the opening of control panel doors to undertake visual examinations or undertake non electrical work near energised equipment. I find that most live working in industrial and commercial facilities is confined to testing, inspections and running adjustments.
Suitably. This word completely changes the meaning of the opening sentence. I often hear when conductors are insulated through finger safe shrouding or cable insulation then live work can proceed with no further precautions necessary. I can name several examples of incidents in switchgear which was finger safe or of Form 4 construction. It is the task or activity near live conductors which will determine whether the insulation is suitable or not. An armoured and insulated underground cable may be suitably covered with insulation where its presence is known and careful location and hand dig techniques are adopted but would not be suitable using a jack hammer without safe dig techniques. Finger safe shrouding, providing it hasn't been removed, may be suitable insulation for routine testing but may not be suitable for the task of drawing in of cables into switchgear enclosures or other similar invasive tasks.
And. Parts a) b) and c) are separated by the word ‘and' which means there is a legal requirement for all parts of the regulation to be satisfied before live work can be permitted.
Danger and Injury. Danger and injury are highlighted in bold and are specifically defined in the guidance documents referred to in this article. Briefly, danger means risk of injury, and injury means death or personal injury from electrical shock, burns or explosion and arcing. For live working, danger may be present but injury must be prevented.
As an electrical duty holder who may be vexed by the questions posed in regulation 14 where do you look for help? Firstly there is the Memorandum of Guidance (HSR 25) published by the HSE. This is usually purchased instead of a separate copy of the actual regulations, to assist with the interpretation of each of the regulations in turn. In addition there is the guidance booklet HSG85 Electricity at Work - Safe Working Practices, also available from HSE Books. Further guidance can be obtained from the HSE website www.hse.gov.uk.
I find HSG85 Electricity at Work - Safe Working Practices is particularly helpful in the decision making process for working live or dead. Simple flowcharts are a feature of this document and one such flowchart is shown below.
It is not my intention to repeat verbatim the advice given in the existing guidance notes but to further expand on this decision making process and to emphasise a methodical process for identifying the risks and the methods for controlling them. I have used the following model many times with duty holders to explain the relationship between the live/dead working decision, task, identification and quantification of the hazard and preventative measures to be taken. As can be seen, this relationship is an interdependent one. It is not sufficient to decide firstly to work live and then devise preventative or protection measures.
To further clarify this relationship, a decision for work to proceed cannot be taken in isolation to other factors. The level of hazard and also the availability and effectiveness of preventative or protective measures will also need to be considered. This is all directly affected by the work task.

Steps to Identify and Assess the Risks and Methods for Controlling them.
The live working decision flow chart Figure 1 illustrates that a critical part of decision making is the identification of risks and the methods for controlling them. I find it useful to break this down into a four step process as follows.
STEP 1:    Equipment and shock hazard
STEP 2:    Electrical flashover
STEP 3:    People and safe systems of work
STEP 4:    Environment
STEP 1 - Equipment and shock hazard
Has the equipment been checked and is it in a safe condition? Check whether the equipment to be worked upon has been examined and in a safe condition for work. Live work should never be permitted where there are any doubts about the safety of cables and electrical equipment being worked upon or even adjacent to those being worked upon. The examination can be visual but also using other senses such as smell and hearing to detect burning or electrical discharge.
Signs of vermin or birds inside switchgear or water ingress is a definite prompt to stop and investigate only when the switchgear is dead and isolated. Approaches should never be made to cables damaged by site traffic or excavation.
Is the equipment finger safe? If the equipment is in a safe condition the next step is to consider whether the equipment is finger safe. If the equipment is not finger safe, can measures such as temporary shrouding be used to prevent contact with live parts? The term ‘finger safe' is defined as no exposed live parts that can be accessed by solid objects greater than 12.5mm as given by IP rating IP2X.
Do not rely purely on the original specification of the equipment. Insulation is often removed and not replaced. If it is not finger safe, or other measures cannot be introduced to prevent contact with live parts then carry out the work dead.
Are tools, instruments and leads checked fit for purpose? If measures to prevent contact with live parts can be implemented, are tools, instruments and leads checked fit for purpose?  Tools and instruments must be of the correct duty rating and their condition must be checked especially test leads. It is important correct instruments and leads should be selected and in particular the correct over voltage installation category in accordance with EN61010-1. The wrong meter and leads can increase the chances of electric shock or the initiation of an electrical flashover due to transient over voltage. Most instrument manufacturers publish guidance about overvoltage on their websites.  
Are you sure the equipment is designed for live operation? There seems to be some opinion that because electrical components ‘plug in' then this operation can be carried out live. Examples of such components are plug in circuit breakers or bus bar trunking tap off units. Always contact the equipment manufacturer if such a live operation is contemplated. You may find the equipment has been designed for flexibility rather than for live operation and the manufacturer may discourage such activities.

STEP 2 - Electrical flashover or arc flash
Is there a significant risk of burns from electrical flashover? I have authored several articles on the subject of electrical flashover in Electrical Review and they can be accessed at www.electricalreview.co.uk. In brief, the severity of the thermal effects of an electrical arcing event is usually expressed in units of calories per square centimetre at the working distance from a potential arc source and the head and torso of the worker. This is called incident energy and a level of 1.2 cal/cm2 is sufficient to predict a 50% chance of the onset of a second degree burn.
Incident energy has an approximate linear relationship firstly; to the amount of current that can flow in the arc and secondly to the time that it can flow before the upstream protective device clears the fault. Note that arcing current does not equal prospective fault current (PFC) and at 400 volts is likely to be less than 50% of PFC. It follows the upstream device may take longer to operate with resulting higher levels of incident energy. Keep in mind also, protective devices need to be maintained to ensure they will operate according to their time current characteristic.
When undertaking arc flash studies for industrial and commercial facilities, I have found, where the upstream protective device is a conventional fuse or fast acting fixed pattern circuit breaker at a rating less than 100 amperes and the voltage is at 400 volts 3 phase and below, then the incident energy levels will be limited. A rule of thumb is to use the good old BS88 Industrial fuse as a model. If the entire time/current characteristic curve of the upstream device can sit below a BS88 100 ampere characteristic curve, the incident energy at a working distance of 450mm is unlikely to exceed 1.2cal/cm2. This does not mean flash burn injury can be totally discounted and severe burns can still be experienced particularly at the hands which will usually be closer any arc initiated when testing live circuits. For comparison, a BS88 400 ampere fuse could present a predicted *20 cal/cm2 at certain fault levels and an 800 ampere fuse could be in excess of *60cal/cm2.
*Note these figures are for indicative purposes only, not to be used in a risk assessment.
Suitable risk control measures must be employed and as a last resort PPE should always be used. In the case of the 800 ampere fuse, PPE is unlikely to fully protect the worker because of the possible ballistic and other effects of a flashover. Regardless of tasks, I recommend electrical workers should not carry out work in high power environments in clothing that can ignite or melt.
If the incident energy at the equipment to be worked on is over 1.2 cal/cm2, then can it be reduced to below 1.2 cal/cm2? As an alternative, can risk controls be put in place to prevent or mitigate arc flash effects and are they adequate? Please refer to my recent articles, available on the Electrical Review web site. If the answer is no to both questions then proceed no further until advice is sought or carry out the work dead.

STEP 3 - People and safe systems of work
Are the workers competent for the task? Regulation 16 from the EAW Regulations 1989 states: "A person shall not be engaged in any work activity where technical knowledge or experience is necessary to prevent danger or, where appropriate, injury, unless he possesses such knowledge or experience, or is under such degree of supervision as may be appropriate for that purpose having regard to the nature of the work."
In the context of live work, technical knowledge or experience means the person should be properly trained and assessed in the techniques being employed but the person must also understand the hazards from the electrical system and be able to recognise whether it is safe for the work to continue at all times including whilst the work is being carried out.
Is the work to be carried out at height? Working on live equipment at height is always a special case for consideration for two reasons:
1. Electric shock or arc flash to a worker at height can bring about a fall with obvious consequences.
2. An arc flash incident whilst working at height may mean that the worker cannot move out of the way because of the limited working space on access equipment. This may be the work platform of a scaffold or a mobile elevated work platform.
If the work has to be carried out at height, can risk control measures to prevent shock, burns and falls be put in place?
Is Accompaniment Required? Anyone undertaking work on or near energised electrical conductors will nearly always require some form of accompaniment by someone who can give assistance in an emergency.  This implies a degree of competence such that the accompanying person can assist without danger to themselves or others.  A requirement for a second person is to ensure safe working procedures e.g. preventing encroachment of non-authorised personnel into the working area.

STEP 4 - Environment
Is access and space adequate? Establish whether the access and space in front of the equipment is adequate to allow the worker to pull back from the conductors without hazard. HSG85 mentions a minimum 915mm measured from a live part or 1375mm when there are live parts exposed on both sides of the worker. The working space may need to be greater than these minimum distances as a result of the electrical flashover assessment in Step 2.
The work area should be clearly defined, with no tripping and slipping hazards and with good means of escape and illumination.  Simple barriers and signs can often be erected for the demarcation of work areas to keep non-authorised staff away and also to protect electrical workers from interruptions at times when they need concentration.
Is lighting adequate? It is also important to check whether lighting levels are adequate for work as well as another requirement in Regulation 15. Use of additional lighting is essential where ambient lighting levels are poor.
Are hazardous conditions present? Check to ensure the immediate environment is free from water or dust. A hostile or wet environment will significantly increase the risk and severity of electric shock and should therefore be subject of special consideration to control the risks. Ensuring there is no possibility of an ignition hazard due to sparks is crucial. If there is a possibility of an ignition hazard, take precautions to remove the hazard before proceeding. There may other local environmental hazards that may need to be taken into account such as automatic fire fighting equipment.

Proceeding with work
After all 4 steps are satisfied, then revisit the flowchart in Figure 1 and confirm the work is justified relative to the precautions, implement safe working and ensure adequate monitoring and supervision. Make sure any special equipment and PPE is properly used and maintained and always keep the duration of any live work to a minimum.

When a power service engineer is called out to deal with a loss of supply on a customer’s HV distribution network, the chances are it will be traced to a faulty underground cable that has caused a device – such as a circuit breaker – to operate and cut-off the power. Danny O’Toole, ABB Power Service, explains

A cable in good condition and installed correctly can last a lifetime - well over 30 years. However, cables can be easily damaged by incorrect installation or poorly  executed jointing, while subsequent third party damage by civils works such as  trenching or curb edging is also another main cause of damage.

Service engineers are usually equipped with a suite of test equipment that enables them to perform an immediate on site check on the key network elements of switchgear, transformers and cables. If the fault is identified in a cable, as it often is, and the network is interconnected, they are then able to sectionalise the problem circuit to restore power to as much of the network as possible, bringing in additional generation if necessary. The next task is to locate the position of the underground cable fault as accurately as possible, since this makes it easier to find and repair so that the full network can be restored quickly.

ABB has developed a fault location regime that has proved very accurate in  locating underground cable faults in both modern XLPE type cables and older PILCSWA (paper insulated lead covered steel wire armoured) designs. Fault location is usually carried out on cable networks up to 11 kV, however the techniques can be applied on cables up to 33 kV.
The main technique employed is the SIM (secondary impulse method) that combines the use of classic high voltage surge generator thumping with low voltage TDR (time domain reflectometry). To see how this works, it is useful to consider the merits of the individual techniques.
Cable thumping
The high voltage surge generator, or thumper, is a portable device that is used to inject a high voltage DC pulse (typically up to 30 kV) at the surface termination of the cable to be tested. If the voltage is high enough to cause the underground fault to break down it creates an arc, resulting in a characteristic thumping sound at the exact location of the fault.

Historically, fault location was carried out by various measuring techniques and by setting the surge generator to thump repeatedly, and then walking the cable route until the thump could be heard. At which point ‘x' would mark the spot to start digging. Naturally, the higher the DC voltage applied the louder the resulting thump and the easier it becomes to find the fault. If the cable is long it could take days to locate a fault by this method. During which time the cable is exposed to potentially damaging high voltage thumping. So while the existing fault might be located, other areas of the cable could have been weakened in the process. Statistically, cables that have been thumped tend to fail sooner than would otherwise have been expected.
TDR (time domain reflectometry) uses a pulse echo range finding technique, similar to that used by sonar systems, to measure the distance to changes in the cable structure. It works by transmitting short duration low voltage (up to 50 V) pulses at a high repetition rate into the cable and measuring the time taken for them to reflect  back from areas where the cable has low impedance, such as at a fault. The reflections are traced on a graphical display with amplitude on the y-axis and elapsed time, which can be related to the distance to the position of the fault, on the x-axis.

A cable in perfect condition will not cause any reflections until the very end, when the  pulse encounters an open circuit (high impedance) that results in a high amplitude upward deflection on the trace. If the cable end is grounded ie a short circuit, the trace  will show a high amplitude negative deflection.

Low voltage TDR works very well for the location of open circuit faults and conductor-to conductor shorts. However, for shielded power cables, it becomes very difficult to distinguish faults with a resistance higher than 20 ohms. Unfortunately, the majority of faults in underground distribution cables are high resistance faults in the area of thousands of ohms or even megaohms.
The SIM (secondary impulse method) technique combines low voltage TDR and a thumper in an integrated system that makes the trace easier to interpret, with a clear indication of the fault location on a handheld display.

The process starts by running a TDR test on a healthy core, this is then stored in the SIM system memory. The thumper is then triggered to send a single HV pulse, and while the arc is forming at the fault the TDR sends a further low voltage pulse. The arc acts as a very low impedance point that causes the pulse to reflect in exactly the same way that it would from a short circuit. The handheld display combines the two traces and the fault location is shown as a large negative dip, with its distance easily read off on the x-axis.

SIM enables a fault to be located to within a few metres, even over very long cable runs of several kilometres. Of course, underground cables do not always take the shortest or most direct route between two points, so it is important to have access to the site cable records. In cases where a map of the cable route is not available a radio-detection system can be used to find the cable, but this could add a considerable amount of time to the exercise. ABB would always advise customers to make a detailed record of their underground cable circuits a priority in their maintenance planning.

Once the target area above ground has been identified, the surge generator is turned on to start thumping the cable. The operator then listens for the thump to home in on the precise location of the fault - this approach minimises the amount of time that the cable is thumped, eliminating the risk of further damage. The next step is to bring in the repair team to dig up the cable, make a visual confirmation of the problem and then effect a repair.

The time taken to locate a fault by SIM varies according to each case, but will typically take around half a day.
Fast track fault location for Silverstone Circuit
Silverstone Circuit, located on the border between Northants and Buckinghamshire, has its own high voltage power network comprising 17 11kV/433V substations that provide local power supplies at key points around the three-mile track. ABB has a long-standing service contract for the network to provide ongoing maintenance and repair services including a fast call-out response in the event of a fault.

At 6am on 1 July 2008 the ABB duty stand-by engineer fielded an emergency call saying that there was a major outage, with a total loss of power to half the site. In normal circumstances this would be a cause for concern. With the British Grand Prix taking place on the Sunday and hospitality organisers and traders already setting up on site, the loss of power threatened to cause significant disruption.

Within an hour, an engineer was on site. After establishing the fault was on Silverstone's own network they opened discussions with Central Networks, the local DNO (distribution network operator) to organise reinstatement of supply. A thorough test and inspection showed the problem was not due to faulty switchgear, but was cable related. So ABB's specialised cable fault location vehicle was called to the site together with spare cable and joints.

While waiting for the fault location vehicle, the fault was successfully sectionalised so that it was isolated from the rest of the network, ensuring it couldn't cause any further loss of power. This step enabled Central Networks to restore full power to the rest of the site at around 9.00am.

The fault location vehicle arrived at 10am, and in less than two hours the cable fault was located to an area beneath the tarmac base under a hospitality marquee erected for the F1 Paddock Club.

The next stage was to expose the identified section of cable for a visual verification of the damage. A further 10m of trench was then exposed to enable a new section of cable to be jointed into place. By 10pm, the jointing operation was finished, pressure tested, energised and phasing proved so that power could be restored to this local section of the network. All that remained was for the trench to be backfilled and recovered by tarmac. So what might have caused very severe disruption in Silverstone's busiest week of the year effectively became a minor incident.

Our grumpy old man's mood has not been lightened by England's recent footballing failures, but the way Forgemasters has been treated has really got his goat

Sorry to be on another quasi-political rant this month, but we British just don't seem to get it right when it comes to competition.

As I write, England have been dumped out of the World Cup at the hands of a rather promising young German team, the abject failure of FIFA to invest in technology that, let's face it, is already mounted in the goals, and most significantly, a lack lustre performance by the men in control - manager and players.

Shortly before the South African debacle however, we scored what in my mind was an even bigger own goal, the coalition government's failure to honour a pledge, made by Labour, to loan £80m to Sheffield's Forgemasters. The money was a loan, not a grant, to enable the company to install a new open die press with which to make large components principally for the nuclear power industry.

This sends out three distinct messages to me. One, our government has no confidence in one of our best heavy engineering companies; secondly there is yet another manifestation of Britain's reluctance to invest in engineering; and thirdly (which is where Electrical Review's readers come in) the failure to recognise the need for such components if we are to press ahead with a nuclear build programme. Readers of this column will know how sceptical I am of this government's commitment to extending our nuclear capacity.

The prize for Forgemasters if it gets its new plant is a very highly competitive edge in the global nuclear energy sector. There are very few forges with the capacity and technology to make the huge, yet tightly toleranced, components required by modern nuclear plants. You can genuinely count them on the fingers of one hand. Our failure to make the loan investment to Forgemasters means the company must now rely on private investors (whose confidence must surely have been undermined by the Government's inaction) or see its golden opportunity fall to India, China or even to Japan, where there already exists one of the handful of other open die plants of its kind.

Don't forget the knock on effect if the forge loan is not forthcoming - it will affect suppliers of all the ancillary machinery that would go around the plant; expansion of the workforce not just at the company but among the many subcontractors also. Extrapolate this further to the impact the increased wealth would have on local economies, retailing and investment.

I know we must have cuts in public spending, public borrowing and the public sector. I seriously wonder however, how an £80m investment in our futures compares with some public sector spending that regularly consume similar sums.  For example, one could commission 400 consultants to work on projects for a year. One could buy a single jet fighter aircraft. I wonder what local government stationery bills come to?

The Revenue's OGC Buying Solutions reckoned it saved £80m in a single year, just by getting public sector buyers to use its ‘Buying Card' scheme. This hints at inefficiencies, but screams them loud and clear when one considers these savings were on just £500m of transactions - thereby representing an annual waste of 15% just on making purchases.

Alternatively, with £80m the government could buy about half the England football team (the cheap half) or perhaps more wisely, could sign Christiano Ronaldo.

In March 2010, the Times reported UK Contractors Group's outlook for the next few years is Deep public spending cuts will lead to soaring unemployment in the construction industry. At the same time, the UK faces challenging carbon emissions reduction targets between now and 2050, which could be jeopardised by the loss of key skills from the sector explains Tony Sung, chairman of CIBSE Group and technical director at Hywel Davies

The sector faces the twin challenges of riding out the toughest recession in living memory, and delivering new or refurbished buildings which consume less energy and emit less carbon. Much of that carbon is emitted by electrical systems, so the electrical services sector is at the forefront of the drive to improve our building stock.

With the latest revisions to Part L of the Building Regulations coming into force in October 2010, and with the recently introduced Carbon Reduction Commitment in place, developers and building owners will have to allocate more resources to adapting their buildings for future climate changes.

The current cost of adaptation, using some technologies that are not 100% tested and proven, is not considered to offer a fast enough payback, and in many cases is seen as  relatively expensive in offsetting the short-term cost of carbon emissions. Several adaptation technologies such as photovoltaic, on-shore wind farms, hydro and wave power, demand large open spaces, or require planning permissions, or both, which can be hard to obtain. There is a growing conflict between the desire of government to cut carbon emissions and invest in renewable, and the willingness of planners to sanction them.

Whilst some building integrated low or zero carbon technologies are well established, such as solar thermal water heating, photovoltaics, or heat pumps, they may require substantial upfront capital investments. There are only a handful of exemplar projects provided by the Carbon Trust and Energy Saving Trust to demonstrate real life energy and carbon emissions reduction. The Technology Strategy Board is funding a number of further projects in this area to demonstrate how buildings can be adapted to meet the requirements of our anticipated future climate, but these will take time to influence and to stimulate investments by the private sector.

The introduction of the Feed in Tariff provides some incentives to install renewable technology, with the prospect of ongoing revenue to encourage initial capital outlay. The tariff came in in April, and it is too early to see how much of an impact it is having on demand. There are therefore a number of measures which can be expected to stimulate demand for electrical services, but not in the immediate future. Whether this demand will materialise in time to support the sector through the current period of reduced workload remains to be seen.

What we ought to see at this time, with the prospect of steadily increasing demand for energy efficient refurbishment and renewable technologies, is increasing training to meet the emerging demand for these skills. But at present training in the sector is falling, as firms, many of them SMEs, cut back on all non essential spending to conserve cash and protect the business.

One of the measures introduced in response to the Climate Change Act is the Carbon Reduction Commitment Energy Efficiency Scheme, or CRC. This started in April 2010, with the primary objective of helping medium to large size organizations whose total half hourly electricity consumption exceeds 6,000MWh, to cut their energy use and carbon emissions. To enable the For CRC to be a success, Britain needs to up-skill the current M&E workforce (electricians, design and installation engineers) competently to apply, install, test and commission the low zero carbon and smart metering technologies in tens of thousands of existing buildings rather than just for new buildings.

Again, looking at the figures for compliance with the requirement for Energy Performance Certificates, Display Energy Certificates and Air Conditioning Inspections, we should be cautious about the prospects of CRC stimulating a whole new wave of activity in the current economic conditions.

Another area of development is the new amended BS7671:2010, currently issued in draft for public comments. This includes vital changes necessary to maintain technical alignment with Cenelec harmonisation documents. One of the perceived advantages of the technical alignment is it should help British companies to win work in the EU.

Cibse, through its Electrical Services Group, provides electrical services engineers with a network of like minded professionals who are active in all of these areas. Through Group events and through the website, http://www.cibse-electricalservicesgroup.co.uk members can access the collective knowledge and expertise of the group. Additionally, Cibse runs a number of events and training courses for electrical services engineers, and recently launched a new web based learning initiative, to provide training in electrical services (and other building services disciplines) that is flexible and adaptable to user needs. Cibse and the Electrical Contractors' Association recently signed a Memorandum of Understanding, which commits both bodies to work together more closely to help develop and deliver electrical skills and services, to better meet the challenges of climate change.

If we are to meet the carbon emissions reduction targets for 2030 and 2050, we will need to see greater investment, both in new technologies and in skills. Cibse will be looking to work with engineers and employers in the sector to deliver both.

By Arnaud Piechaczyk, R&D Group Leader, Nexans International Research Center

Fire-resistant cables play a crucial role in applications where it is essential to ensure the integrity and continuity of vital safety circuits during the critical building evacuation and fire fighting periods required by stringent national and international standards. In many cases, the need for cables that can deliver the required levels of performance, reliability and safety has forced designers and installers of electrical systems to compromise on other desirable properties regarding ease of handling and installation.

Now though, a major advance in the materials science related to the properties of the cable insulation – called Infit – is making it possible to produce new families of electrical power and data cables with outstanding fire resistance using classical extrusion methods. The result is a user friendly cable that offers the ‘best of both worlds’.

Eliminating the need to chose between insulation technologies
Until now, the cable industry has mainly relied on two major technologies to insure the integrity of flexible cable insulation during a fire: XLPE/Mica taping and ceramic forming silicone rubbers.

Each of these technologies presents a number of advantages. The classical insulation taping based on Mica, and largely used since the 80s, can easily be implemented on an industrial scale to provide a tough, effective electrical insulation when overlaid with a cross-linked polyethylene (XLPE) coating. It is strong but stiff to handle, so can present some installation difficulties.

On the other hand, silicone rubber insulation can be extruded directly on to the conductors, and offers a good compromise between fire performance and ease of installation thanks to its flexibility. It is, however, vulnerable to cuts and tears.

Increasing customer demands for improved fire performance, together with strippability, ease of installation and connection prompted Nexans to search for a new insulation technology that could offer all these benefits.

Infit transforms into a tough insulating ceramic layer
Infit is a unique, proprietary innovative technology that combines, in a polymeric material, the advantages offered by both the tough mica tapes layer and the extruded silicone insulation layer. This now enables the manufacture of fire-performance cables that are both tough and easy to handle as well as being easy to strip and install.

Infit technology offers enhanced fire-performance because when the insulation is exposed to fire, it transforms from a flexible, plastic covering to a tough insulating ceramic layer, hardening like clay in a potter’s oven to form a protective shield. The key to the success of the new insulation has been in using advanced materials and polymer science to optimize the nanostructure of the primary insulation materials. A combination has been found that reduces the occurrence of cracks or breaks in the insulation to preserve the operational integrity of the circuit i.e. preventing short-circuits.

Extensive laboratory tests have shown that cables with Infit insulation will to continue to deliver power in the event of a fire, long after the plastic sheath and insulation have burnt away. This means, for example, exit lighting, smoke and heat exhaust ventilators, fans or pumps will still function reliably, even in areas directly affected by fire, ensuring safe evacuation.

The science part
The new technology is the result of some ten years of development by the Nexans International Research Centre based in Lyon, France, working in close partnership with the Australian Nexans R&D Centre. The successful outcome of the project has been based on fundamental studies that especially highlight the synergy between ceramic science and the latest polymer science.

In classic ceramic science, a well defined curing process is followed to form a high performance ceramic. Yet, in the case of accidental fire, the temperature increase is sudden and unmanaged. So the first challenge was to develop a ceramic forming system able to react and form an electrical insulating shield in a very short time across a wide range of temperature increases, while also exhibiting a high level of electrical insulation.

The second parallel challenge was to achieve this performance using an extrudable formulated polymeric material, rather than a powder, that was also suitable for the very demanding standards of the cable industry. As a result, Infit technology is principally based on filled copolymers of polyolefins (like polyethylene). This kind of polymeric matrix is well adapted to the extrusion process, and well known in the cable industry - but it is also intrinsically highly combustible. However, Infit uses the synergy between this combustible matrix and a mixture of inorganic fillers to create a new insulating material that offers superior fire-performance.

Infit applications
Depending on the specific cable application, the new insulation material can be offered in either a cross-linked or thermoplastic version. This will enable cables to offer the ideal combination of fire, mechanical, electrical or thermal properties optimized for each application.
Infit is a proprietary Nexans technology, and can be implemented in compliance with many worldwide cable standards, and according to the most rigorous product quality and safety criteria. Nexans cables insulated with Infit can, for example, resist fires reaching temperatures of around 1,000°C, at voltages up to 1kV, exhibiting a high level of char cohesion and electrical insulation.

Infit is gradually being deployed across the Nexans fire resistant product ranges. This will include power, communications, control and LAN cables for use in public building and industrial applications and it is expected to be of particular interest to the marine sector.


Who would have thought that something as simple looking as a cable cleat could cause so much debate, but in recent years it has been one of the hottest topics in the electrical industry - not least because the recently introduced International standard has elevated its prominence to a whole new level. Unfortunately, the problem with this prominence is that the importance of a cleats role in any electrical installation is still not fully appreciated. Therefore, we've decided to try and rectify things by talking cleats with Richard Shaw, managing director of leading cleat manufacturer, Ellis Patents.

ER: First things, first, why do we need cleats?

RS: For an electrical installation to be deemed safe cables need to be restrained in a manner that can withstand the forces they generate, including those generated during a short circuit, and this is job that cable cleats are specifically designed to do. 

Take them away and the dangers posed by a short circuit are obvious - costly damage to cables and cable management systems, plus the risk to life posed by incorrectly or poorly restrained live cables.

And it's important to bear in mind that it's not just the use of a cleat that is vital, but the use of a correctly specified cleat. Because all an underspecified product would do in a short circuit situation is add to the shrapnel.
ER: Well that seems fairly straightforward, where's the problem?

RS: The key issue surrounding cable cleats is that their importance has been, and still is, severely underestimated. Therefore, instead of being treated as a vital element of any cable management installation they are simply lumped in with the electrical sundries. 

What this means in practice is that even if suitable products are specified, they are still seen as fair game for cost-cutting when it comes to companies seeking to keep within tight budgets. This is a potentially dangerous practice that, if allowed to continue, could lead to the wholly unnecessary loss of a life.

ER: Have the International (IEC61914 - 2009) and European (EN50368) standards not helped deliver this level of awareness and education?

RS: Yes, the introduction of the two standards was a huge boost for everyone associated with cable cleats. And yes, they have helped to provide global recognition of the need for secure cleating in electrical installations, which when you consider that as recently as 2003 there wasn't even a European standard for cleats demonstrates just how far we've come in the journey towards the widespread adoption of safe cleating practice. 

But, they still fall some way short of ensuring the cleat is universally understood and used correctly. The main reason being that the standards are advisory rather than regulatory, meaning that the onus is on the manufacturer to self certify their products - a situation that has led to a market awash with a mish-mash of products of differing quality, which in turn means further confusion for specifiers and installers.

ER: What needs to be done then?

RS: Compulsory third party certification really should clear up this confusion, but the problem is that the quoted short circuit withstand, which is seen as the indicator of a cleats suitability for a project, is only valid for a cable diameter equal to or greater than the diameter of the cable used in the test. 

So if the project in question is using smaller cables than those referred to in the test (and the fault level and spacing is the same) then the force between the cables is proportionally greater, meaning the certificate is inappropriate and the cleats will not provide the protection they are installed to give.

What all of this means is that at present the only tried and tested way to ensure correct cleating is through project specific testing - a process that we currently offer customers that means they can install our cleats with complete confidence.

ER: You've talked a lot about short circuits, can you explain what happens to cables during a short circuit situation?

RS: We do a lot of short circuit tests and a good way of explaining what happens to the cables is to look at the difference between those that are correctly restrained and those that aren't. 

In recent tests we did with our American distributor, kVA Strategies, we performed three short circuit tests on 3 x 1/C-777kcmil, 2kV marine cables at 59kARMS in trefoil formation. One test was conducted on cables tied with 1/2" wide stainless steel cable ties, while the other was conducted on cables restrained by our Emperor trefoil cable cleats. During the short circuit the mechanical forces between the cables exceeded 4,500 lbs/ft.

After one short circuit, the cables restrained with the metal cable ties were damaged beyond repair - suffering multiple tears in the cable jackets and insulation, as well as evidence of electrical arcing. In fact, the metal cable ties catastrophically failed before the first quarter cycle current waveform peak, ejecting the ball bearings from the cable tie buckles with sufficient velocity to lodge deeply into the plywood test bay walls. The subsequent cable thrashing also severely damaged the cable tray.

In contrast, the correctly restrained cables were subjected to not one, but two successive short circuits and after careful inspection no damage was found. In fact, the testing lab team stated that the cables still passed the required IEC voltage withstand test and so could continue to be used at full-load.

ER: Aren't electrical cables meant to be fully protected by circuit breakers?

RS: That's a common misconception, but in the event of a fault the forces between cables reach their peak in the first quarter cycle, while circuit breakers typically interrupt the fault after three or even five cycles. And by this stage, if the cleats are underspecified, the cables will be long gone.

ER: What's the best cleat to use?

RS: How long is a piece of string? There are a large variety of cleats available and all of them are designed for different installations. For example, our Emperor cleats are recommended for the highest short circuit fault duty applications. Meanwhile, our Centaur cleats are designed specifically to restrain high voltage cables up to 400kV with a diameter range of 100 to 160mm.

ER: So, is there a rule of thumb for picking the appropriate cleat for an application?

RS: In order to ensure the correct cleat the best idea is to go to a manufacturer with information concerning the installation environment, mounting structure, cable configuration, peak short circuit fault level and cable diameter and they should be able to advise on the most suitable cleat and the spacing at which it should be installed.

ER: And what about a recommended spacing between cable cleats?

RS: Again there's no hard and fast rule to suits all installations. The optimum spacing needs to be determined by engineering calculation to ensure the cable cleats are suitable for the electromechanical forces encountered during the maximum available fault duty of the system.

ER: Finally, the use of multi-core cables, which we are told don't need to be restrained, is growing enormously - what's your view on this?

RS: This is a question we are being asked with increasing regularity and so in order to be able to provide meaningful advice we have carried out some preliminary research and carried out a series of short circuit tests. 

At present we aren't aware of any published data that indicates any preferred particular fixing method, but custom and practice suggests that most users seem to working under the assumption that any forces on the conductors that arise in the event of a short circuit will be restrained within the cable jacket, meaning cable cleats aren't required. 

The tests we carried out were on armoured and unarmoured 3 core, copper conductor, multi-core cables from various cable manufacturers. These cables were tested across a variety of conductor sizes but because of the number of manufacturers, the variety of cable types and the different methods of construction available, it wasn't feasible to carry out exhaustive tests. 

That said the results of the tests, although varied, were certainly interesting. They showed that it is unsafe to presume that the forces between the conductors will always be restrained within the jacket of the cable, whether or not the cable is armoured or tightly helically wound. 

Therefore, our conclusion is that unless the relevant cable manufacturer can give assurances regarding the performance of their specific multi-core cable at the anticipated fault level, then fault rated cable cleats provide the safest option for securing multi-core cables.

For further information about Ellis Patents visit www.ellispatents.co.uk  or call 01944 758589.

The increasing sophistication of emergency lighting systems means specifiers need to take account of many different factors to ensure the end user gets the best value. Stewart Langdown of Tridonic highlights some key issues

While there are many areas where building operators can cut back to save money, emergency lighting is not one of them. Not only do they have to install emergency lighting, they also need to ensure it is regularly tested. Clearly the latter is something that can prove to be a time-consuming and expensive business when carried out manually.

To that end, there are now many more systems available that will automatically test emergency lighting, and it's important to ensure such systems address all of the relevant criteria. These include issues such as the compatibility of the control gear with modern light sources like LEDs, the level of overall controllability and whether the system is stand-alone or integrated with other lighting controls - and there are various sustainability considerations too, as well as issues such as choice of light source and batteries, which can also have an impact on the design of the emergency luminaire. And the fact of the matter is that not all emergency lighting controls are equal; some offer considerably greater functionality and ease of use than others.

Clearly, the fundamental requirement for an emergency lighting control system is to ensure the emergency lighting works when it's needed. Above and beyond this, the majority of end users will now expect a system that incorporates self-commissioning and self-testing features for continuous monitoring, weekly function tests and annual duration testing. Five pole technology to ensure total isolation and compatibility between the ballast, inverter and supply system is another critical factor.

Such self-testing usually represents a worthwhile investment as it reduces the requirement for maintenance staff to walk around the building and carry out a visual inspection - freeing them for other duties. However, different systems offer different levels of functionality so it's useful to be aware of some key points.

For example, the self-testing function needs to be easy for maintenance staff to use, perhaps with a simple combination of different coloured LEDs to indicate correct functioning or to indicate the nature of any fault. The important thing here is the ways that status is indicated are very clear with no room for misinterpretation.

Another factor is convenience. One of the required tests is a weekly 30 second test to establish and confirm the functionality of the unit, battery and lamp. However, this can be inconvenient for the occupier so it's useful to be able to pre-programme each unit to run the test at a different time, to avoid all units testing at once.

Ideally, the unit will delay the test until the normal lighting supply has been switched off for longer than two minutes - minimising the risk of the test being carried out while the occupier is present. In the event that the supply is permanently connected or the lights are left on permanently the unit should ‘force' a function test after a further 21 hours.

Cut out the middle man
As noted above, self-testing takes some of the pressure off the maintenance team but there is still a requirement for a visual check to determine whether the emergency lighting unit has indicated a fault. So it makes sense to take advantage of the recent advances in controls networking, by integrating the emergency lighting testing with the lighting management system. This is a very straightforward process using the popular DALI(Digital Addressable Lighting Interface) protocol.

The DALI system allows luminaires to be addressed individually, so that detailed information can be monitored for each fitting. In addition to standard information such as indicating faults on the lamp, control gear or battery, the system can provide information on, for example, the device status, type of lamp and type of emergency unit and battery.

As a result, with the emergency lighting linked to a DALI lighting management system, information on the operating status can be displayed centrally together with the precise address. Any faults can then be corrected efficiently with no need for maintenance staff to patrol the building, resulting in even greater savings in terms of time and maintenance costs. Crucially, the system should also maintain a complete log of all such events as proof of compliance with emergency lighting regulations.

Furthermore, use of DALI for both emergency and general lighting reduces installation requirements as the overall amount of cabling is reduced, thus saving on site time and raw materials. The result is a more sustainable project, with less embodied carbon, as well as the financial savings on materials.

In addition, use of appropriate control components within a DALI system can facilitate commissioning and increase the likelihood that the system will perform as it was designed to. For instance, the EZ easy addressing feature of Tridonic EM PRO DALI Invertor that uses the indicator light emitting diode (LED) light source) to indicate the DALI address during commissioning.

Where required, the DALI system can also be linked to the building's IT network using an interface between DALI and the TCP/IP protocol used by local area networks and the internet. This makes it easier to access the functions and can be achieved via the organisation's intranet, or across the internet from any location. For organisations with an extensive estate of many buildings across a wide geographical distribution this is a very useful feature, particularly if the facilities management or maintenance management function is located at a single location. This scenario has become increasingly common as organisations seek to rationalise their resources by making better use of technology.

Light sources
Just as importantly, the system needs to be compatible with the latest light sources. For example, many fluorescent lamps now use a mercury amalgam rather than liquid mercury as this is safer. So the system needs to be compatible with amalgam lamps (some aren't). It also needs to work with both cadmium and nickel metal hydride batteries.

Similarly, where linear fluorescent lamps are used, T5 is increasingly the first choice, generally in a low profile fitting that takes advantage of the compact nature of the lamp. Here, it's the important that the emergency lighting control/self-test module has a low profile so it can fit in the luminaire.

One of the characteristics of T5 lamps is they burn at a higher temperature than other linear fluorescent light sources, so for the test to be meaningful the testing module should operate the lamp at twice the normal emergency power level for 55 seconds. This ensures the lamp is correctly heated to ensure maximum lumen output during the most critical switch over phase, achieving greater visibility of potential dangers.

Increasingly though, the light source of choice for emergency lighting is the LED. LEDs offer lower energy consumption, which is important for emergency light fittings such as exit signs that are on most of the time, as well as much longer life, again reducing maintenance requirements. In addition, the use of compact LED light engines facilitates the use of smaller and more discreet luminaires to meet statutory lighting requirements, which can often help with the aesthetic side of the design.

This is further facilitated by the choice of battery, as newer battery designs enable fewer, smaller batteries to be used. This has the added benefit of reducing environmental impact. Of course, integral power control technology should ensure maximum emergency light output for a given duration time with a minimum battery cell count in consideration of LED tolerances.

The choice of control gear is also important for use with any light source and can assist in standardising the type of module across different emergency light fittings. For instance, it is possible to use the same module for testing for one hour,  two hours and three hours duration, operating single or multiple LEDs wired in parallel. Similarly, a 2W module may be used to power a single LED at 600mA or two LEDs at 350mA in series. This level of flexibility helps in minimising the number of different components that need to be specified for a project, while retaining maximum flexibility in choice of emergency lighting fittings.

With fluorescent lighting that's used for both mains and emergency lighting, the choice of control gear can make a significant difference to the life of the lamps. Ballasts that deliver a warm start to the lamp will maximise lamp life and enable high switching frequency applications with very low power losses and enhanced thermal management. Ballasts should also incorporate voltage protection to prevent damage in the event of a mains voltage rise above a pre-defined threshold. In the case of compact fluorescent lighting ballasts with insulation displacement connection can enable automatic wiring, thus saving time.

In fact, these are just some of the many examples of how the choice of system components can make a significant difference to the performance of the system. The important thing is to be aware of these details and keep abreast of the latest developments.

Uninterruptible Power Supplies UK sales manager, Mike Elms, explains how modular  UPS systems can help cut your energy bills

The need for qualifying organisations to reduce their energy usage is highlighted by the Government's Carbon Reduction Commitment Energy Efficiency Scheme, or ‘CRC', which came into effect on 1 April this year. With the scheme rewarding qualifying participants who perform well, while penalising those who do badly, in both financial and publicity terms, it's clear simply finding ways of reducing energy use is not enough; it's essential that these improvements have long term sustainability. Developments in uninterruptible power supply (UPS) technology offer one way of achieving sustainable energy savings.

Maintaining continuous supply power from uninterruptible power supplies (UPS systems) is now considered essential by organisations running financial, healthcare or industrial processes that depend on vulnerable ICT equipment. As UPS units are installed in the critical supply path, any improvement to their efficiency will make an appreciable contribution to their operators' energy management strategies.

Such efficiency improvements are possible, through selection of suitable UPS topology and by carefully sizing the UPS system to match its critical load. One increasingly popular approach is to use systems based on advanced modular topology, which allows UPS capacity to be closely matched, or ‘right sized', to the critical load size. Modular UPS capacity can easily be incremented or decremented to efficiently match changing load requirements throughout the life of the installation - a sustainable efficiency solution.

As well as saving energy and helping to meet CRC targets, modular technology allows significantly smaller, lighter UPS installations with increased power availability. By looking at what modular technology is, we can better understand its benefits and their practical application.

On-line, static double conversion UPS systems first appeared in the seventies and are still in use today. Their principle of operation is to rectify incoming AC mains into DC, which charges a battery before being inverted back to AC to drive the UPS critical load. In the event of AC mains failure, the battery can take over the role of supplying DC to feed the inverter until the incoming AC mains is restored. In early designs the inverter was followed by an output transformer, necessary to restore the output AC voltage to the same level as the mains input. However advances in power semiconductor technology and the introduction of the Insulated Gate Bipolar Transistor (IGBT) have allowed changes to the UPS design which permit elimination of the output transformer. This yields a number of advantages, the most important of which relate to improved efficiency, reduced size, and weight.

Energy efficiency is improved for a number of reasons. With no transformer core to heat there are no iron losses; with no windings there are no copper losses. Both factors contribute to energy savings. Transformerless designs also exhibit lower input current harmonic distortion (THDi) and an improved input power factor, which both reduce energy. Eliminating wasted energy also reduces heating effects, and therefore cooling costs. Further energy savings arise from modular technology which, as we shall see, is made possible by transformerless design.

Eliminating the transformer reduces the UPS's size and weight by something like 66%. This is a large reduction which has had a profound effect on the way UPSs are seen and used. Uninterruptible Power Supplies Ltd (UPSL) realised that a 3-phase UPS rated up to 50 kVA could be implemented as a rackmounting module rather than a large standalone unit. And implementing a UPS as a set of modules in a rack rather than a single standalone unit gives great flexibility as well as space savings. This flexibility allows right sizing, with a UPS solution that's closely matched to its load. The result is less capital and space wasted on unnecessary capacity together with maximised operating efficiency. An example shows the efficiency savings possible:

Let's imagine a site with a load of 96 kW and a power factor of 0.8, which demands a 120 kVA supply. We'll also assume that, for security, N+1 redundancy is required. That is, N UPS units have sufficient capacity to completely support the load, so in an N+1 configuration, one unit's failure would still leave sufficient UPS capacity to support the load. This would typically be implemented in a standalone system using two 120 kVA units, each of which would only be 50% loaded during normal operation. Efficiency with legacy transformer based design would be 90%. By contrast, a modular system could be implemented using four 40 kVA modules, where each module is now 75% loaded. As well as being smaller, lighter and more easily expandable, its efficiency would be 96%, which more than halves the cost due to losses per year. The annual cooling costs are also more than halved. At 7.84 p/kWh, total annual savings would amount to over £5000pa.

If our site load remains at 96 kW throughout its operation life, the annual £5000 savings will continue with no further action needed. In real life however, the load is not only likely to change, but the extent of its change can defy prediction. In a typical scenario a data centre may be expected to be initially loaded to 35% of its capacity, with this load growing steadily to 90% of capacity over a period of 10 years. With a standalone UPS, the response is typically to install a system sized for 90% data centre capacity from the outset, to avoid the difficulties of upgrading or replacing it later. These include finding more floorspace in a crowded data centre, disrupting business operation with building work and installation, and laying or repositioning cabling. However, such an oversized system would spend its operational life greatly under loaded, adding reduced efficiency to unnecessary capital costs and space requirements. This would be exacerbated if the load does not grow to the expected 90%. While the UPS's conservative rating should ensure that the load would always be supported, it's not unknown for the actual load to exceed projections so that new UPS capacity must be supplied after all.

These difficulties can be avoided by using a modular system. Its flexibility means it can easily be expanded or reduced after being initially rightsized to its load. There is no need to oversize it initially because modules can be added without disruption as and when they are needed. This flexible property of modular UPS topology is known as its scalability, and it's a scalability that has two dimensions - vertical scalability and horizontal scalability.

The example above has four 40 kVA modules totalling160 kVA capacity, or 120 kVA with N+1 redundancy. These modules could populate four out of five slots in a single server-style floorstanding rack. Vertical scalability is a reference to the fifth slot, which can be populated to increment capacity at any time. Additionally, a second rack could be provided for an incremental increase in floorspace and cost. The ability to add further racks in parallel is known as horizontal scalability. This adds up to enormous flexibility, with UPS configurations over 1 MVA being possible.

The task of efficiently maintaining right sizing to the critical load, however unpredictably the load grows, becomes simple. The modular approach allows the maximum possible energy efficiency as well as minimising capital and space costs throughout the life of the installation.

Steve Gallon, managing director of Finnish enclosure manufacturer, Fibox, confirms its aim is to offer a range of enclosure products that meet both the exacting standards of an ever changing industry, and the specific needs of their diverse customer base

When a designer is faced with the specification of an enclosure to house and protect a specific device or control system, there is an art to getting the exact enclosure product to fulfil the requirement exactly.

To some specifiers a box is a box is a box. But nothing could be further from the mark. Invariably the enclosure is the ‘nutshell', housing expensive and often critical components which must perform in extremely harsh and demanding conditions. Therefore a number of very important questions must be asked, and answered, before the purchase order can be signed. That is why it is crucially important that the relationship between specifier and manufacturer must be such that all the following points are covered at the design stage. It's a bit like the signs those of us who enjoy a tipple see above the bar stating that change should be checked because alterations can't be made later.

The conundrum facing a lot of specifiers is they have a series of enclosures from various manufacturers to choose from, and on the face of it they all look the same. They are grey, plastic and have hinged or removable covers. What they don't see is the suitability of the different ranges for a particular application, especially when one considers the increasing amount of direct copies using cheap blends of plastic being introduced into the market now from all areas of the globe.

The secret to getting to the nub of what enclosure is fit for purpose is knowing which questions to ask a manufacturer. Then it is equally important for the manufacturer's representative to have the knowledge to be able to offer constructive advice and guidance to ensure the exact enclosure solution is identified quickly and efficiently.

At this crucial stage in a product's introduction cycle it is very important to take into account that there are many individuals in the decision chain. Each link in the chain has a different specification priority. It could be the marketers requirement for aesthetics or the R&D/design wngineers need to download CAD drawings from a manufacturer's website. When pulled together, all these differing facets will make the final decision to purchase a particular enclosure failsafe.

So let's look at the key criteria which when addressed will very quickly narrow the choice down to just a few options:

Where is the enclosure likely to be installed, inside or outside?

This determines the material choice, the IP rating and any specific corrosion risks which need to be addressed at the design stage.

What is being installed in the enclosure?

This solves the size issue and also answers the question of what type of internal fixing points are required. Some manufacturers can offer extra fixing pods to accommodate cover mounted components etc.

How often is access to the interior required?

Should the design include hinged opening doors for regular access? Alternatively should the design include security such as locks or tamper proof cover screws to guarantee total integrity of the enclosure?

Does the enclosure require visual access to the internal components?

By answering this question the option of transparent or opaque covers is addressed. This could include the provision of viewing windows in an opaque cover for example.

Does the enclosure need to delivered, already customised?

This is a very important question often asked by specifiers who do not have in-house machining facilities. Customising includes machining of holes and apertures, special fixing points, graphics and corporate colours, and a multitude of other bespoke services. Some manufacturer's offer a comprehensive customising service and this should always be discussed with them at the design stage.

What is the budget price?

This question has to be addressed at some point so why not cover it at the early stage of the project! Manufacturers can then offer alternatives and compromises to assist the specifier in achieving their cost criteria.

By forming a partnership with a manufacturer who has the capability to provide a ‘one-stop-shop' for all the specifiers various requirements, this not only keeps the project in as few hands as possible from design to delivery, it ensures that cost issues are transparent at every stage. The fewer links in the supply chain, the better the overall control.