NEC 500 Class I/Div I Purged Junction Box Requirements

[BigMotorGuy]

We run a test stand that is rated Class I/Div I hazardous area in which we run multiple electric pumps from low voltage up to 6600v. Since we install and tear down the pump connection setup on a daily basis (hence the test stand designation), we do not have the luxury of having sealed AEx e junction boxes, but rather use typical NEMA 4X with a nitrogen purge. However, again due to the test stand nature (i.e. build/tear down daily), the purged JB's do not even use glands. We simply run the cable through the JB cutout and leave gaping holes between the box and the cable.

Question.....what are the requirements for purging typical NEAM 4X JB's for meeting class I/Div I?

Any help would be appreciated....

 

[GroovyGuy]

Hi BM Guy,
Class-1 Div-1 is a tough call, more so for a test-stand. Obviously if this was a permanent installation, the proper cable glands would be required. I'm sure that with the proper monitoring of the N2 flow, this can be made into a safe, almost legal, installation. But I am not sure how you would go about satisfying the NEC.

Have you already done the gas-detection / forced ventilation / automatic shutdown thing? In Canada, and I'm sure in the US as well, this can be used to drop the Division down to Div-2, which is a step in the right direction.

I have used the purged method before (or y-purge), usually with air and not N2. These systems have always used in pressure switch (or transmitter) to ensure that the enclosure is always pressurized. This, of course, will not work unless the entry cables are properly glanded, (which in your situation they are not).

I don't believe that you can use NEMA 4X enclosures in a Div 1 area. Don't Div-1 boxes need to be cast, or use factory-sealed devices?

BTW, what is the nature of the test stand? Is it for testing pumps,or for testing motors/drives? I think it must for testing pumps. but I am not sure. What is the flammable stuff? Liquid or gas or both? Are vapours heavier or lighter than air?

 

[itsmoked]

I don't believe that you can use NEMA 4X enclosures in a Div 1 area. Don't Div-1 boxes need to be cast, or use factory-sealed devices?

I thought by virtue of the purge you can use NEMA 4.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[GroovyGuy]

Hi Keith,
I have use air-purge (ie z-purge) on many installations in Div-2 areas with NEMA-4 boxes. Div-1 areas are quite rare, but I am sure that one can air-purge (ie y-purge) with NEMA-4 boxes there as well.

My comment "I don't believe that you can use NEMA 4X enclosures in a Div 1 area." is wrt what I believe that a motor OEM will normally provide on a motor designated for Class-1 Div-1 rating. ie I have never seen a motor OEM supply anything other than cast explosion-proof boxes on such a motor. The motor OEM will not have designed the motor for N2 or air purge, and therefore would not have provided NEMA-4 boxes.

It is also worth noting that most motors installed in a refinery, gas-plant, or other facilities handling flammable liquids or gases, are not explosion-proof (ie Div-1 rated), but are essentially normal motors suitable for Div-2 areas. These motors may be designed & built to more stringent standards (ie API-541, 547 or IEEE-841), but these motors are not "explosion-proof".

I was wondering if the OP really has a Class-1 Div-1 area, and if these motors have NEMA-4 boxes, how can these motors be Div-1 rated?

 

[itsmoked]

Ah, I see Groovy. Thanks for clarifying that for me.

I could see the motor makers offering a "purged" version but then maybe not if they don't want some yahoo using a purged version in an EXP application, especially if they've already built a unit that's been 'approved'.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[drawoh]

BigMotorGuy,

I am working on a similar enclosure. We are working to ATEX EX_p, as opposed to the explosion proof EX_d. A subcontractor is building a gas purge system for us, which includes a gas detector. The system turns on. The gas detector detects nasty gases. The purge system turns on. When the gas detector stops detecting nasty gases, everything else turns on. We do have a power supply upstream of the purge system which must be and is explosion proof.

--
JHG

 

[BigMotorGuy]

To All, correction, the boxes are actually cast Div I boxes, but that assumes you use a rated gland which we do not at this point.

The area is a Div I since it is in the immediate area for a submerged LNG pump electrical feedthru. I guess the easiest answer would be to seal the cable with a gland, but this is not practical since it is a test setup only. I am looking into getting some sort of pneumatic expanding gland that is easier to install/uninstall which will provide some sealing benefits and continue with the N2 purge we currently use.