Class 1 - Div 1 Electrical Enclosure 1

[angleburt]

I have a request to upgrade a standard controls enclosure to satisfy class 1 - Div 1 (actually it is for a project in India and their request is Gas Group IIA/B, Zone 1, T4, I interpret this to be class 1 - Div 1)
In the past, we have used enclosures with a purge (z-purge specifically), but for this application it is not desired.
Is it as simple as installing the components, (PLC, Relays, circuit breakers) into a Nema Type 7 enclosure, and using rigid conduit and appropriate rated fittings to make the connections to the equipment?
Thanks in advance
Angleburt

 

[dpc]

The concept behind explosion-proof electrical enclosures is that if there is an electrical arc inside the enclosure and this ignites explosive gases INSIDE the enclosure that the escape path for the hot gas from the inside of the enclosure to the outside will cause sufficient cooling of the gas so that it will not ignite the surrounding air.

In the US, you would generally have to get this all tested and approved by UL or ETL or some similar "third-party" testing agency. So if I buy an explosion-proof motor starter, then replace the contactor inside with another manufacturer's, technically, I no longer have an official explosion-proof motor starter. In India, I have no idea.

If this is all low-energy stuff, you might be able to qualify it as intrinsically safe.

 

[JLSeagull]

The 2008 NEC handbook should be helpful for these Class I issues. Both the gas groups and zone designations are covered in the NEC. The gas groups IIA and IIB are described in Article 505.6. The Temperature codes and types of protection are covered in article 505.9. Look for the protection designations for the equipment that needs to be installed. Some PLC components are available with the necessary ratings. This could reduce the quantity and size of the NEMA 7 boxes.

Within the NEC you can use zone rated enclosures for a process area in lieu of division rated enclosures but you cannot mix systems. In a like manner, compliance with the NEC suggests applying the proper zone rated enclosures, etc.

As dpc mentioned, if you need to modify a NEMA 7 enclosure to mount devices, this must be done in a special shop that is certified for such purposes. Don't just permit the shop to drill into the cast box.

If appropriate, in addition to the NEC Handbook, obtain a copy of the applicable Indian Standards. I get after Indian suppliers that lack familiarity with the current US standards for equipment installed in the USA.

 

[angleburt]

Thank you JLSeagull.

I understand the implications of modifing an enclosure, I was just not sure about installing these components without a purge, but it sounds achievable provided the correct pieces and parts are selected (obviously not by me, but someone specializing in this area)

Thanks again.

 

[DRWeig]

Hi Angleburt,

I've done many similar projects. Make a sketch of your control panel and show the location and size of all the conduit entries you'll need. Send it to the explosionproof enclosure makers (their distributors will forward). Appleton, Crouse-Hinds, Killark, and my favorite, Akron Electric.

They'll return a quote to make you a NEMA 7 box for your purpose.

Be careful with the installation. Bolt torques need to be even and according to specs. Don't let the polished flange faces get scratched -- the gap is designed to dissipate heat from an internal explosion, cooling escaping gases to a level that won't ignite anything outside. A good scratch can nullify the rating.

Be careful about moving toward intrinsically safe classification. All devices in your panel would have to be listed (except simple things like RTDs and switches) and protected with barriers. You'd likely have to change every part...

Let us know how it goes for you!

Good on ya,

Goober Dave

 

[controlnovice]

Be careful:

An enclosure with a UL stamp of being rated for Class I, Div 1 does NOT mean that it is approved for a Zone 1, Group IIA/B, T4 area.

Even with same temperature and gas ratings, the approval stamp on the equipment must match the area rating.

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