C1D1 Dual Enclosures w/purge

[justdavemamm]

I have two enclosures (one for a PLC & associated equipment, the other for a VFD) that are in a Class 1 Div 1 area. They are X purged serialy using one purge control unit and connected with 2" air pipe. The distance is about 4 feet total of conduit between the enclosures.

All devices external the the enclosures are either I.S. (w/isolators) or XP, with seal-offs.

Do I need seal-offs for metal conduit that runs only between the two enclosures ? Currently they are there at each end, both for the conduit that has 24vdc wires and another one that has the 120vac wires. Again, about 4 ft of 1/2" metal conduit connects them.

Some people here tell me that no seal-off should be needed for the conduit between the two enclosures. I would agree if the conduit run didn't contain any couplings or fittings, but they do (NEC 501.5 (A)(3)).

Any thoughts on what code section applies for this or permits no seal-offs ? Personally, I don't care or mind putting them in. It's the non-electrical people here that argue they aren't required and want to save a real few dollars - which has more then been negated by the time used by arguing about it.

 

[rbalex]

Re: C1D1 Dual Enclosures w/purge

501.5(A)(2) Pressurized Enclosures. In each conduit entry into a pressurized enclosure where the conduit is not pressurized as part of the protection system. Conduit seals shall be installed within 450 mm (18 in.) from the pressurized enclosure.

In the installation as you have described it the conduit between the enclosures is not required to be sealed.

 

[petersonra]

Re: C1D1 Dual Enclosures w/purge

Thats a confusing paragraph. The first sentence is not even a complete sentence, its more like a condition for the second sentence.

It seems to me the real issue is that the conduit between the boxes is protected by the presurization system, and thus the area inside those conduits is not hazardous. Think of it this way, the pressurization in effect creates a non-hazardous sub-area in what would otherwise be a hazardous area.

 

[justdavemamm]

Re: C1D1 Dual Enclosures w/purge

Yeah, 501.5(A)(2) tells me when I DO have to have a seal off: when it's NOT part of a pressurized protection system. I wish it would also say when I don't.

So, going on the premise that if it's doesn't say it's required, it's not then I don't need them.

Since 501.5(A)(2) is explicitly stating "Pressurized Enclosures" rules, it takes precedence over 501.5(A)(1), right ?

 

[rbalex]

Re: C1D1 Dual Enclosures w/purge

Then read it this way:

501.5 Sealing and Drainage. Seals in conduit and cable systems shall comply with 501.5(A)?
?
(A) Conduit Seals, Class I, Division 1. In Class I, Division 1 locations, conduit seals shall be located in accordance with 501.5(A)(1) through (A)(4).

Does the conduit appear to be one of the 501.5(A)(1) through (A)(4) applications? If not, it's not required to be sealed.

Trust me

[ December 01, 2004, 02:20 PM: Message edited by: rbalex ]