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On the safe side

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Martindale Electric looks at what’s needed to stay safe when working on electrical plant equipment and identifies simple solutions to ensure equipment safety ratings match the application.

Safe isolation procedures are in place to ensure that workers on-site are not exposed to danger when working on or near live electrical systems and equipment. Both the standards for the equipment and the potential penalties for non-compliance have changed recently.

With around 1,000 serious accidents in the workplace each year and 16% of all fatalities linked to electricity, it’s clear to see how following simple safe isolation procedures and using the correct equipment can keep your team safe and avoid heavy penalties for non-compliance which can exceed £10m. In fact, changes to sentencing guidelines for health and safety offences have resulted in average fines trebling over recent years.

What do electricians and maintenance teams need?

The essential equipment needed to stay safe and achieve compliance with the regulations are:

  • Locking off devices
  • A clear method of labelling the hazard 
  • A dedicated voltage indicator
  • A proving unit to verify the voltage indicator.

Comprehensive locking off kits are available to ensure the right locking off device is always to hand. A basic kit should include the following; a selection of MCB a breaker locks, a padlock with a unique key, a hasp if more than one person is working on a system and lock out tags and warning labels.

However, locking off the circuit correctly is just one part of the procedure. Before carrying out any work on the circuit, it is essential to prove the circuit is dead. Circuits are frequently mislabelled so there is no certainty that the correct circuit is locked off.

Dead certain

Multimeters are not suitable as it’s all too easy to select the wrong range. They rely on battery power to function, so it’s possible to make a false ‘dead’ reading on a live circuit if the batteries are flat.

When it comes to choosing the right voltage indicators, there are a number of suitable models on the market which are fully compliant with the latest standards, so what features should be taken into account?  

Apart from the obvious issue of reliability, many voltage indicator models now come complete without batteries, ranges or switches to worry about, which increases user friendliness. When it comes to test lamps, many models, such as the MTL10 and MTL20 from Martindale, also bring added benefits of a 360° viewing angle, even in bright sunlight with high density LEDs indicating four voltage bands of up to 690V.  When selecting a test lamp, it is also important to look for a model which comes with interchangeable right angled and straight probes to ensure easy access, even in difficult to reach locations. As an added precautionary measure, a finger barrier also helps to ensure a safe distance from line conductors.

Proving true

The procedure for proving dead is to test the voltage indicator or test lamp against a known source, such as a proving unit, then test the circuit, then test the voltage indicator against the known source again to prove the tester is functioning properly.

It’s recommended to use a dedicated proving unit matched to the voltage indicator to fully test that all LEDs on all ranges are working. A proving unit is safer than the mains and provides a live source wherever you are working.

When it comes to choosing the right voltage indicator, one of the main factors that sets many voltage indicators apart is a 1,000V CAT IV safety rating in accordance with BS EN61010 and it is this safety rating which makes indicators such as the VI-15000 and MTL15 suitable for supply side LV applications in all installation categories as defined in the standard. 

BS EN61010-1 Installation Categories (CAT ratings) define the risks from hazardous transient impulses and potentially lethal short circuit currents on the mains supply system based on where you are working.

Test equipment used for measuring LV circuits will have a CAT rating to show where it can be used. Each category also has a voltage rating to show the maximum safe phase to earth system voltage, normally 50V, 100V, 150V, 300V, 600V or 1,000V.

To ensure safe working practices, it’s critical to match the test equipment safety rating to the installation category. Typically CAT II includes socket outlets and similar points of the mains installation, CAT III the distribution part and CAT IV the supply side source of the building’s mains installation. Testers, leads and accessories all need safety ratings equivalent to or higher than the installation category and voltage rating for the location to be safe.


In order to simplify selecting the right tools, many manufacturers now offer kits which provide a complete solution which are widely specified by contactor and maintenance teams to ensure compliance with health and safety regulations and keep those who work on or near electrical systems safe.


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