When it comes to electrical safety in the USA there are two main organizations who set safety standards: NEMA (the National Electrical Manufacturers Association) and UL (Underwriters Laboratories). NEMA is the association of electrical equipment and medical imaging manufacturers in the United States. UL is a safety consulting and certification company headquartered in Northbrook, Illinois which maintains offices in 46 countries.
As both organizations set safety standards it is inevitable that some standards overlap. However they have been set independently, so the different organizations’ standards are different. The ratings are, however, based on similar application descriptions and performance expectations.
The key difference between the two sets of standards, is in the area of testing. The UL standards require that manufacturers arrange independent testing of their standard compliance, using independent evaluators. Possibly because NEMA is of course a manufacturer’s association, the NEMA standards have no such independent testing requirement, and they are happy for manufacturers to monitor their own compliance.
The NEMA standards being scrutinised are in NEMA Standards Publication 250-2008 – Enclosures for Electrical Equipment (1000 Volts Maximum). The relevant UL standards are UL 50 – Enclosures for Electrical Equipment, Non-Environmental Considerations and UL 508 – Industrial Control Equipment.
Electrical enclosures are cabinets for electrical or electronic equipment to mount switches, knobs and displays, which are designed to prevent electrical shock to equipment users. They also protect the contents from the environment. NEMA has described a number of different types of electrical enclosures, defined in NEMA ICS 6: Enclosures standard. NEMA and UL do have differing definitions of what is included in each rating, however. For the purpose of this comparison, the NEMA terms will be used.
Type 1 Electrical Enclosures
- Type 1 is the baseline for both organizations. All the other types build on with degrees of hazard or complication. Basically for both organizations, Type 1 is an electrical enclosure built indoors. It really has two purposes. The first aim of this enclosure is to keep people away from parts that could be hazardous to them. UL specifies this as “incidental contact”, so these low-level enclosures are really designed to stop people touching live electrical parts, accidentally.
- The only real kind of environmental protection provided by Type 1 enclosures is against falling dust. Electrical systems are enclosed, stopping dust from getting into their innards (and thus disrupting things or causing overheating and a potential fire hazard).
- Type 1 electrical enclosures often house things like motor start & stop stations. They often have a latching door, but they are not required to have a sealing surface and therefore they are not suitable for applications that require sealing out dust, oil, and water.
- Apart from the language used and the issue of independent testing, the Type 1 standards are the same for both organizations.
Type 2 Electrical Enclosures
- Type 2 sees a small, but important, advance on the Type 1 specifications. Both NEMA and UL consider Type 2 devices to have all the protection enshrined in Type 1 devices – any hazardous parts will be out of accidental reach of people and the enclosures will stop dust from settling on the equipment. Likewise, Type 2 devices are designed for indoor use. The key extension is that these devices also provide some protection against water (and other non-corrosive liquids, according to the UL definition) getting in. Even then, however, the protection is only against dripping and light splashing (both standards are consistent on that point).
- A Type 2 enclosure is often fitted with drip shields in order to protect electrical components from failing as a result of contact with water, possibly caused by conditions where there is high condensation, such as cooling rooms or laundry rooms.
Type 3 Electrical Enclosures
- Type 3, which is again described similarly by both standards’ organizations, is one major jump up from Step 2. Type 3 electrical enclosures are robust enough that they can be used in outdoor situations, as well as indoor ones. The full Type 3 description is slightly more encompassing than the variations that follow.
- Type 3 devices have all the protection enshrined in Type 2 devices – any hazardous parts will be out of accidental reach of people and the enclosures will stop dust from settling on the equipment. There will be some protection against water (and other non-corrosive liquids, according to the UL definition).
- The key extensions in the Type 3 definitions are firstly that these enclosures will clearly be more robust to cope with the outdoors and secondly these products provide protection against windblown dust (as you would expect in an outdoors setting). Where there is a big jump in specification is that the water protection not only covers drips and splashes, but also rain, sleet and snow. It is also a requirement of both versions of this standard that the enclosure (and the equipment within in) will be undamaged by sheet ice forming on the enclosure.
- It is very clear. If you have a need to use an electrical enclosure in an outdoor setting, Type 3 units are the minimum specification (allowing for some of the changed capacities in the Type 3 variants below) that you should consider.
- Type 3 is seen as being weather-resistant. It protects against weather hazards such as rain and sleet. It is often used outdoors in places like ship docks, construction work, tunnels and subways.
Type 3R Electrical Enclosures
- Both NEMA and UL recognise Type 3R, a variation of Type 3, and again, the standards cover the same specifications (with the usual wording differences and need for independent verification). Type 3R enclosures are of a similar design to their Type 3 counterparts, but they have ventilation in. This means that they have less protection against windblown dust (and thus the “windblown dust” wording has been removed by both organizations from their definitions).
- The ventilation is often achieved through the use of louvered openings to filter the air within the enclosure. The reduced protection can to some extent be offset through the use of screens or in some cases air filter material put in the back of the louvered openings.
Type 3S Electrical Enclosures
- Type 3S is an extension on Type 3. Under both organization’s definitions Type 3S devices include all the protections offered by Type 3 (thus they can be used indoors or outdoors, in areas prone to rainfall, sleet, snow and windblown dust). These particular electrical enclosures also include external mechanisms that remain operable when ice-laden.
Type 3X Electrical Enclosures
- Type 3X appears in the NEMA documentation, but there does not appear to be an UL equivalent.
- As with the basic Type 3 enclosure, Type 3X enclosures can operate indoors or out. They offer all the protections of the standard device against rain, sleet, snow and windblown dust.
- Where the 3X devices have an advantage over other enclosures, particularly in difficult conditions, is that there these devices have extra corrosion-proofing, which could be particularly useful in places like ship docks.
Type 3RX Electrical Enclosures
- Type 3RX also appears in the NEMA documentation, but does not have an UL equivalent.
- These enclosures, as the name suggest, have a mixture of the 3R and 3X specifications. Namely, they provide protection against falling dust (but not windblown dust). Electrical systems are enclosed stopping dust getting into their innards. They provide protection against water getting in, including rain, sleet and snow. They also provide protection against ice on the enclosure. The 3X part of their specification adds extra protection against corrosion (including protection against ice forming on that extra protection). The 3R part of the definition recognises that they are likely to be ventilated, limiting their protection against wind-blown dust.
Type 3SX Electrical Enclosures
- Type 3SX is likewise in the NEMA documentation, without an UL equivalent.
- These devices have both the 3S and 3X protections. This means that they have external mechanisms that, to meet the standard, must remain operable even when ice-laden. They will also have extra protection which can be of benefit in situations where corrosion has the potential to be a problem.
Type 4 Electrical Enclosures
- The protection offered by Type 4 enclosures ramp things up further. Again, the difference between the NEMA and UL definitions are just the language used, and the need for independent checks.
- These devices are once again usable both indoors and outdoors. They have all the protection of Type 3 enclosures. The extra protection at level 4 relates to protection from splashing water and hose directed water. This means that these enclosures can survive a wash-down from a commercial hose.
- Type 4 enclosures are used for highly sensitive electrical equipment because of the high level of protection from the elements. They are often called rain-tight enclosures due to their excellent weather resistance. These enclosures are generally gasketed with doors that clamp to provide a maximum seal.
- They are often found outdoors on ship docks, in dairies, and in breweries.
Type 4X Electrical Enclosures
- Type 4X enclosures are typically used in difficult industrial and corrosive environments that where the needs exceed the capabilities of the basic Type 4 enclosures. Interestingly, although UL does not appear to recognise the Type 3X variants they do have Type 4X in their list of standards. Type 4X enclosures are generally manufactured using particular types of stainless steel that have a high degree of protection from corrosive materials.
- These enclosures tend to be used in places, such as meat/ poultry processing facilities, which have total wash-downs with disinfectants occurring repeatedly, as well as petro-chemical facilities, including offshore petroleum sites.
Type 5 Electrical Enclosures
- The focus with the Type 5 enclosures is ensuring that they are dust-proof.
- There is one key difference in the Type 5 ratings between NEMA and UL. NEMA accepts that Type 5 devices can be used both indoors and outdoors, whereas the UL specification unequivocally states that they are for indoor use.
- Despite this, the specification, in regards to water, is equivalent to Type 2, so it would be rare for a Type 5 enclosure to be outside.
- Basically, any hazardous parts will be out of accidental reach of people These devices provide some protection against water (and other non-corrosive liquids, according to the UL definition) getting in, but, this protection is only against dripping and light splashing.
- The dust extension provides protection against falling dirt and settling airborne dust, lint, fibres, and flyings)
Type 6 Electrical Enclosures
- The focus for both standard organizations when they specified Type 6 protection was for those enclosures that are submersed. These enclosures have most of the protection of the Type 4 ones (with the exception of wind-blown dust) and they add extra protection against occasional temporary submersion at a limited depth. Likewise these enclosures should be able to cope with ice forming on them. The NEMA definition does not specifically mention rain, sleet and snow (although the UL definition does), however if the enclosure can survive submersion in water and ice encasing it, it presumably should be able to manage rain and sleet.
Type 6P Electrical Enclosures
- Type 6P enclosures are even more robust than the basic Type 6 ones. They have all the features of the Type 6 model, but they add in two crucial differences (in both NEMA and UL definitions). Firstly 6P enclosures need to be able to stand submersion (to a limited depth) in water or other liquid, such as oil, for a prolonged period of time. These enclosures, like the 3X and 4X ones, have extra protection against corrosion.
- Depending on the exact needs, both Type 6 and 6P enclosures have uses in quarries, mines, and manholes.
Type 7 Electrical Enclosures
- Types 7, 8, 9 and 10 enclosures are specifically designed to be used in hazardous conditions.
- The Type 7 enclosures are designed for use in hazardous internal locations. The NEMA standard describes these as being designed to contain an internal explosion without them causing any external hazards. The UL specification basically says the same thing, but in much more technical language, namely “Indoor use in hazardous (Classified) locations classified as Class I, Division 1, Groups A, B, C, or D as defined in NFPA 70.”
Type 8 Electrical Enclosures
- Type 8 enclosures are also for use in hazardous situations. The UL standard for Type 8 is identical to that for Type 7, except if adds the capability of outdoor usage. NEMA specifically states that these enclosures are intended to prevent combustion through the use of oil-immersed equipment.
Type 9 Electrical Enclosures
- These enclosures are designed for use in a different type of hazardous internal location to those where Type 7 enclosures are located. The NEMA standard describes these as being designed to prevent the ignition of combustible dust. The UL specification continues to use more technical language, namely “Indoor use in hazardous (Classified) locations classified as Class II, Division 1, Groups E, F, or G as defined in NFPA 70.”
Type 10 Electrical Enclosures
- The NEMA Type 10 definition is actually identical to their Type 7 definition. The UL definition makes things clearer referring to these being enclosures which are built to meet the requirements of the Mine Safety and Health Administration, 30 CFR, Part 18.
Type 12 Electrical Enclosures
- Type 12 enclosures are relatively general-purpose. They are in many ways an extension on the Type 2 enclosures. They are intended to be used for indoor use, however still offer protection from faling dirt, dust and noncorrosive liquids that are dripping. They have met resistance tests for dripping, dust, and rust. The UL definition specifically states that these provides protection against light splashing and consequent seepage of oil and non-corrosive coolants. Both the NEMA and UL definitions specifically state that these enclosures are constructed without knockouts. These enclosures often protect manufacturing control or automation equipment, for example for packaging, or material-handling applications.
Type 12K Electrical Enclosures
- Type 12K enclosures are the same as the standard Type 12 ones, except they are constructed with knockouts.
Type 13 Electrical Enclosures
- Type 13 enclosures are again an advancement on Type 2 internal ones. They are also general-purpose. Their main use is to provide protection against dust, spraying of water and noncorrosive coolants. They meet oil exclusion and rust resistance design tests. In other words, they are the same as Class 12 devices, but with extra protection against spraying, splashing or seeping oil and noncorrosive coolants.
- As with most of these types, the only difference between the NEMA and UL definitions is the language used.
The National Electrical Manufacturers Association has set up a number of different levels of protection that can be provided by electrical enclosures. They have also provided standards that producers of these enclosures should meet, at each level. Being an association of manufacturers, they have made their standards self-administering. There is no requirement for any independent check on the enclosure manufacturer’ claims.
Underwriters Laboratories, who specialise in producing various types of standards, has created their own standards in relation to the different types of electrical enclosures. Manufacturers who want to claim that they have met these standards have to get their products independently verified.
The two organizations’ standards, are very similar, and apart from wording differences there are just a few variations of content in relation to a couple of the types.