Specifiers must assess enclosure construction before specifying products as the incorrect choice can lead to significant and costly consequences. They should also make sure they fully understand the system of IP ratings, to avoid incorrect choices and spending more money than necessary. here, Darren Hodson from Schneider Electric explains the system of enclosure ratings, discusses the differing materials available and highlights one of today's most common misconceptions surrounding the ratings standards - IP69K
The various enclosure materials available have their strengths and weaknesses and in order to specify the most appropriate material, these must be fully understood. In addition, the importance of the right quality enclosure is critical. The role of an enclosure is to protect valuable electrical components and personnel and it just doesn't make sense to save a few pounds by purchasing an inferior product to protect high value systems. A substandard enclosure could result in leaks, damage to equipment, and possibly even become a hazard to the public. If this happens not only is the user faced with the cost of replacing the enclosure, there is also the cost of changing any damaged components, downtime and possible litigation.
It is critical the same level of time and investment goes into choosing the right quality enclosure, in order to reflect the time and money spent in developing the system it contains and the system(s) it is connected to. Choosing the right material for the job is also an important consideration. Buying a high quality enclosure, but in the wrong material, can be a costly mistake.
Depending upon the application and the preference of the customer, there are three common materials which enclosures are manufactured from: mild steel, stainless steel and GRP. But regardless of the material used, each enclosure should be chosen to suit the specific application they are intended for and this includes having the appropriate IP rating. IP ratings are defined in the IEC 60529 standard for degrees of protection provided by enclosures, published in the UK as BS EN 60529.
The degrees of protection are specified by the letters IP, followed by two or more digits. The first digit (1 to 6) depends on the protection given by the enclosure to equipment within it against the ingress of objects, and also the protection of persons against contact with live parts of equipment within the enclosure. The second digit (1 to 8) relates to the protection of equipment against the harmful ingress of water. Either digit can be replaced by ‘X' for an unspecified condition.
Optional supplementary letters can be used to specify only the protection of persons against access to hazardous parts, and to stipulate special conditions, such as use for high-voltage apparatus or under specified weather conditions.
In general, a higher number represents better protection, although specifiers should be aware this isn't always a guarantee, as sometimes an enclosure might, for example, pass the tests for IP67 but not to a lower rating such as IP65.
It is important specifiers fully understand the conditions of use for an enclosure, as simply specifying a high IP rating does not necessarily mean it is right for the job. The designations refer to the ability of the enclosure to pass the tests under controlled conditions, not to its ability to withstand influences such as weather, sunlight, corrosion, or extremes of temperature. A product can meet the highest level for protection against ingress of water, yet be subject to rusting, so customers must make clear what they are actually expecting from an enclosure rather than relying solely on an IP rating.
In addition to IEC (BS EN) 60529 there are two other standards widely used for enclosures; IEC (BS EN) 62262 ‘Degrees of protection provided by enclosures for electrical equipment against external mechanical impacts (IK code)' and IEC (BS EN) 62208 ‘Empty enclosures for low-voltage switchgear and control gear assemblies - general requirements.' BS EN 62262 uses the letters IK followed by the numerals 00 to 10 to specify the enclosure's ability to withstand mechanical shock including direct impact.
These ratings are used across all materials including mild steel -the UK's most popular choice. This type of enclosure is suitable for most indoor applications. With IP ratings up to IP66 and a high IK rating, it is robust and strong in many environments. The fact that it is easily modified is another reason why it has remained a popular choice for so long. However, specifiers are gradually realising its weaknesses. Mild steel has poor anticorrosion properties if the material is not treated, and this treatment is usually expensive. In addition, cut-outs made after painting must also be protected, adding yet a further cost.
As an enclosure material mild steel still has its place. For general purpose enclosures, either indoors or in industrial and commercial premises, it is a cost effective solution but the fact it corrodes so quickly makes it an unsuitable choice for any external applications.
Stainless steel has been a popular material choice for decades, typically used within the food manufacturing, food processing and pharmaceutical industries as well as for most external applications. It provides the same benefits as a mild steel enclosure but with greater longevity in aggressive environments. It is also rust resistant, however depending on the grade and the environmental conditions, tarnishing and corrosion can occur. Stainless steel also has its own natural finish and so requires no further treatment.
GRP is best suited to outdoor applications as it does not corrode in damp/wet conditions, even when exposed to sea salt. It also offers excellent protection against UV rays and therefore it won't discolour. Being an insulator it offers extra peace of mind on public access sites and so GRP is fast becoming a major competitor to steel with its insulation, strength and corrosion resisting properties over a temperature range from -50oC to 150oC.
GRP enclosures are designed for the wide variety of aggressive applications in which they are used. In addition to the material, which is double insulated, self-extinguishing and halogen free, there are a number of anti-vandal features which make unauthorised access difficult. The list of industries that now accept GRP enclosures is growing and includes security, airports, highways, rail, utilities, telecoms and agriculture.
It is also important to remember, especially when considering harsh environments, high IP levels are not necessarily an indication of a product being weatherproof. Other design features such as canopies also contribute to the enclosure providing the correct level of protection.
IP ratings are invaluable in ensuring enclosures meet the correct standard however it is not always straight forward, as highlighted by one of today's most common misconceptions - requests for enclosures rated IP69K. At first sight, when you consider the rules for IP codes there is no such thing, since this rating is not mentioned in any of the standards mentioned above. In fact it stems from a German national standard developed for use specifically in the automotive industry.
DIN 40050-9 adds to the IEC 60529 rating system with an IP69K rating for high-pressure and high-temperature wash-down applications. The IP69K test specification was initially developed for electronic equipment on road vehicles, but has also been used in other areas such as the food industry, where the use of pressure washers is common.
This standard is purely a German national one and currently has no real meaning in the UK or other countries, as it doesn't feature as part of a British or International standard. A project is now underway to incorporate its requirements into IEC 60529 but initial attempts by various test houses found the test equipment and procedures were not precisely defined by the DIN standard. This means they do not give the same result when performed by different test houses, and so cannot be compared. Some research has resulted in a proposal to modify IEC 60529 to include the designation IPX9, but this is still at an early stage, and needs more work before it can be published as an amendment to the standard.
In the meantime buyers of enclosures should be aware that ‘IP69K' products from different manufacturers may differ, and might not even pass the tests for IPX5. They should also remember that even the IEC 60529 tests are fairly short, up to 30 minutes for IPX7, although longer immersion can be agreed as part of IPX8. As a result they do not define the enclosure's ability to withstand long-term influences such as weather conditions. It is also often forgotten the ‘water ingress' tests do not specify that no water must enter; they allow water to enter but not in quantities that are considered to be ‘hazardous', which of course cannot be determined without knowing what apparatus will be within the enclosure.
Today's enclosures offer a wide choice of materials and the breadth of products available is always expanding but specifiers and designers should remember that correct material specification is vital in achieving product longevity. And it is impossible not just to choose an enclosure with the highest IP rating and expect it to do any job, in any environment. Specifiers need to carefully assess the conditions of use and prescribe the IP rating that is most appropriate and importantly one that is recognised by IEC or British Standards, as well as choosing the appropriate material for their enclosures.