Correlation Between NEMA Enclosure Type and NEC Area Classification? 2

[KernOily]

Hi guys. Please help out a poor dumb mechanical engineer here. I have searched the forum and the web and have not yet found an answer.

Question: Is there a direct correlation between NEMA enclosure type and NEC/API area classification?

For example, I have a solenoid-operated valve that is rated by the manufacturer for NEMA 4X. Does that mean it is acceptable for use in a Class 1 Div II atmosphere?

I gotta believe somebody has made up a table someplace... surely I'm not the first guy to have asked this question.

Thanks guys! Pete

 

[PHovnanian]

Not really. The NEC hazardous area classifications and NEMA environmental ratings address two different issues. The former is fire/ignition/explosion safety and the latter is to provide equipment with some degree of protection from an environment.

There may be some correlation between environmental protection and hazardous location listing, but that is only coincidental. The ratings are entirely separate and both must be satisfied for a properly designed system.

If you need something listed for Class 1 Div II, NEMA 4X doesn't guarantee that. The device or enclosure has to be listed for Class 1 Div II.

 

[DRWeig]

If your solenoid valve contains only a solenoid (no switch or relay), and it does not arc or spark in normal operation, it does not require an explosionproof enclosure. NEMA 1, NEMA 3, NEMA 4, NEMA 4X, NEMA 12, and all the other ordinary location enclosures are fine. In a Div 2 location, an explosionproof enclosure is not required (NEMA 7 or 9) for stuff like solenoids, transformers, and the like. Read the NEC on Class I Div 2 locations in article 500. Watch the maximum temperature rating, too. It has to be below the autoignition temperature of the gas/air mixture in question.

Anything that arcs or sparks in normal operation, such as a switch, contactor, relay, motor with brushes, etc., has to have an enclosure rated for Div 1 (NEMA 7 or 9). You won't find enclosures rated for Div 2. It either has to be Div 1 or ordinary-location types.

You can find assembled products rated for Div 2, they are normally labeled "non-incendive." As PHovnanian said, the enclosure types do not directly correlate to NEC rules.



Best to you,

Goober Dave

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[KernOily]

Guys thanks for the great replies. This is exactly what I needed.

I will go back to the manufacturer and see if this device has been rated for Cl 1 Div 2.

Thanks again!!! Pete

 

[DRWeig]

You're welcome, KernOily --

But there should be no need for an actual Class I Div 2 non-incendive rating, but it would be extra comforting from a liability standpoint. Solenoids are specifically named in the NEC.

I'm back at my desk now. Here's the reference from 2011 NEC:

Paragraph 501.105(B)(3) [regarding electrical equipment in Class I Div 2 locations]

"Without Make-or-Break Contacts. Transformer windings, impedance coils, solenoids, and other windings that do not incorporate sliding or make-or-break contacts shall be provided with enclosures. General-purpose-type enclosures shall be permitted."

Best to you,

Goober Dave

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