Enclosure protection - IEC vs NEMA
In this short post we look into the subject of ingress protection (IP) of enclosures used in variable frequency drives, switchgears etc. First we explain the classification of ingress protection according to IEC standard (“European practice”). Afterwards we introduce the North American practice defined in NEMA standards. Finally we try to find equivalents between those two worlds.
Enclosure as integral part of VFD design
Most VFDs have a metal enclosure as an integral part of their design. There might be some cases with IP00 execution (“open type”). However, those are rather seldom in industrial applications. One can find such open type design in specific tailor made installations, for example an HVDC converter station or railway intertie.
1. Protection against dust and pollution
The enclosure provides a protection against dust and other pollution. For this prupose suitable air filters at the inlet section are required. Although most VFDs are installed in electrical rooms, a clean environment cannot always be granted. it does not mean that the ambient is very polluted. However, even a very small concentration of dust or other particles would build up inside the VFD affecting its performance or eventually causing a failure.
2. Personnel protection (live parts, moving parts, fault scenarios)
Enclosure also serves as a protection against touching the live parts, hence contributing to safety and allowing to stay in the vicinity of the VFD while it is energized. Enclosure helps to contain the electric arc inside or to release it in a defined direction that does not endanger the personnel (ducts, overpressure flaps). It also provides protection against hazardous mechanical parts (moving parts that are hazardous to touch). The safety aspect is obviously very important.
3. Part of cooling concept
Moreover, the enclosure is often part of the cooling concept, especially for air-cooled VFDs. It guides the cooling air to flow through a well defined path and increases the cooling effectiveness while reducing the auxiliary power for cooling. In case of liquid-cooled drives, the enclosure together with the cooling system may allow to decouple the ambient air temperature from the VFD internal temperature. This is very useful for installations with high ambient temperature, such as in “hot” countries (Middle East, India, Africa) in the situation when the HVAC fails.
4. Improved electromagnetic compatibility
Good enclosure design is also effective against electromagnetic emissions and contributes to the goal to fufill the EMC requirements.
IEC world
The applicable standard is IEC 60529 [1]. It applies for the classification of degree of protection by enclosures for electrical equipment with rated voltage up to 72.5 kV. The degree of enclosure protection is defined with respect to:
- Protection of persons against access to hazardous parts inside the enclosure
- Protection of the equipment inside the enclosure against ingress of solid foreign objects
- Protection of the equipment inside the enclosure against harmful effect due to the ingress of water
Further objectives of the standard are the designation of those degrees of protection and the corresponding requirements, and testing to verify that enclosure meets these requirements.
– Designation
The designation starts with IP (International Protection) followed by first characteristic numeral (numerals 0 to 6, or letter X) and second characteristic numeral (numerals 0 to 8, or letter X). There are optional two more letters: an additional letter (A, B, C or D) and a supplementary letter (H, M, S, W).
“X” is used in case characteristic numeral is not required to be specified or not defined.
First characteristic numeral – Protection against ingress of solid foreign objects and protection of persons against access to harmful parts:
0 … non-protected
1 … ≥ 50 mm diameter
2 … ≥ 12.5 mm diameter
3 … ≥ 2.5 mm diameter
4 … ≥ 1.0 mm diameter
5 … dust-protected
6 … dust-tight
Second characteristic numeral – Protection against ingress of water with harmful effects:
0 … non-protected
1 … vertically dripping
2 … dripping (15° tilted)
3 … spraying
4 … splashing
5 … jetting
6 … powerful jetting
7 … temporary immersion
8 … continuous immersion
Examples:
IP54 (no letters, no options)
IP2X (omitting second characteristic numeral)
IP20C (using additional letter)
NEMA world
In North America the National Electrical Manufacturers Association (NEMA) standards provide among others the requirements on enclosure. The applicable standard is NEMA Std 250. Additional standards are UL 50 and UL 50E.
– Enclosure ratings
Type 1
Indoor use to provide a degree of protection to personnel against access to hazardous parts and to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt).
Type 2
Indoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt); and to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (dripping and light splashing).
Type 3
Indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt and windblown dust); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow); and that will be undamaged by the external formation of ice on the enclosure.
Type 3R
Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow); and that will be undamaged by the external formation of ice on the enclosure.
Type 3X, Type 3RX, Type 3SX, Type 4, Type 4X, Type 5, Type 6, Type 6P, Type 7, Type 8, Type 9, Type 10, Type 12, Type 12K, Type 13 – description available for our premium subscribers.
Coming to the subject of this post, we intend to compare the IEC and NEMA approach with regards to enclosures of electrical equipment . The focus is naturally on VFDs, but similar conclusion is valid for other equipment such as switchgears, distrobution panels etc.
NEMA vs. IEC enclosure rating
Below table tries to assign the NEMA enclosure protection to the equivalent IEC designation. Note that exact match is generally not possible due to somewhat different approach in the standards. The table shall therefore be understood as an indication. There is no way to unambiguously convert IEC enclosure designation to NEMA type ratings or vice versa. In general, NEMA standards meet or exceed the IEC standard requirements. Therefore, the conversion from IEC to NEMA equivalent does not work.
Where two alternative IP codes exist to a given NEMA type (depening on literature source and interpretation), the first one is the one most cited by authors whereas the less common alternative is stated in brackets.
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Summary
Enclosure plays a key role for the mechanical and electrical protection of equipment as well as for personal safety. Almost all industrial VFDs include a metal enclosure as part of their design. The rating (IP code) depends on the selected VFD model, cooling type etc and ranges typically from IP21 (air-cooled drives) up to IP54 or even higher (liquid-cooled drives). NEMA/UL standards provide somewhat different classification of enclosures. A rough conversion of NEMA rating to corresponding IEC designation was provided at the end of our post.
References
[1] IEC 60529 Degrees of protection provided by enclosures (IP Code)
[2] NEMA 250 – Enclosures for Electrical Equipment (below 1’000 V)
[3] UL 50 – Enclosures for Electrical Equipment, Non-Environmental Considerations
[4] UL 50E – Enclosures for Electrical Equipment, Environmental Considerations
Selected enclosure manufacturers
Delvalle – Industrial enclosure solutions, https://www.delvallebox.com/en
NEMA Enclosures, https://www.nemaenclosures.com/
The Enclosure Company, https://www.enclosurecompany.com/
