Bonding for conduits in a repair garage

[raider1]

Hypothectical situation,

A RMC conduit that passes through a major repair garage floor (Class 1 division 2 area) and meets the requirements of 501.15(B)(2) Exception #1 and does not require a boundary seal. The circuit supplies receptacles above the Classified location and originates at a panel located in an unclassified location, so the only thing in the class 1 div 2 location is an 18" section of RMC. Does the entire circuit and conduit need to meet the bonding requirements of 501.30(A)?

Chris

 

[rbalex]

Yes it does; but keep the exception in mind - it may not be quite as bad as you think.

It is difficult for me to explain the rationale for this since I disagree with some of it. Essentially, CMP14 wants the "intended" ground fault path to have the absolute lowest impedance possible. The concern is that part of a ground fault current could possibly follow an extraneous path and cause an arc in an unintended Class I location. I buy that for Division 1, but find it excessive in Division 2.

 

[ivsenroute]

I too would agree yes. I am happy that this is hypothetical because I am trying to figure out how small the class 1 div 2 would have to be since not even couplings are allowed on the conduit to meet this exception. Great question.

 

[rbalex]

I too would agree yes. I am happy that this is hypothetical because I am trying to figure out how small the class 1 div 2 would have to be since not even couplings are allowed on the conduit to meet this exception. Great question.

Remember the OP specifies 501.15(B)(2) Exception #1. In the case of the garage the Division 2 location is up to 18" above the floor [See 511.3(C)(1)(b) assuming no ventilation] The raceway stubs up through it and there are no couplings.

BTW the stubup application to avoid boundary seals is very common in Classified locations.

 

[RETRAINDAILY]

the last time i did a repair garage the classified area extended 3' below the slab.

 

[RETRAINDAILY]

if your underground in a class 1 div 2 don't you follow 514.8 and have to be sealed

 

[raider1]

Yes it does; but keep the exception in mind - it may not be quite as bad as you think.

It is difficult for me to explain the rationale for this since I disagree with some of it. Essentially, CMP14 wants the "intended" ground fault path to have the absolute lowest impedance possible. The concern is that part of a ground fault current could possibly follow an extraneous path and cause an arc in an unintended Class I location. I buy that for Division 1, but find it excessive in Division 2.

My feelings as well, especially if the underground portion of the raceway is PVC as permitted in 501..10(A)(1)(a) Exception.

Thanks Guys for your replies.

Chris

 

[raider1]

if your underground in a class 1 div 2 don't you follow 514.8 and have to be sealed

This is a major repair garage without motor fuel dispensing facilities so Article 511 would apply.

Chris

 

[rbalex]

the last time i did a repair garage the classified area extended 3' below the slab.

Depending on how long ago it was, that may have been true, but it was because the NFPA Tech Committees (TC) for NFPA 30A, 88A and 88B at the time didn't really understand "underground" Classified locations. Those TCs have subsequently been dissolved and reformed under a single TC and document.(NFPA 30A) The new TC is a bit better educated on the subject, although there are still some divergent opinions between them and CMP14 that oversees NEC Articles 500-516. They should be resolved over the next few cycles for both documents, but because they have different Proposal cycles it will still take a while.

In the meantime, since the NFPA 30A TC specifies certain installation means and methods and electrical area classifications within their document and it doesn't create a safety hazard, CMP14 has opted to use most of their relevant text until the issues are fully resolved since now there are only minor economic affects.

 

[rbalex]

if your underground in a class 1 div 2 don't you follow 514.8 and have to be sealed

This is one of the "divergent" issues I mentioned in another post. You will note however, Figure 514.3 now recognizes the underground is not actually classified Division 1 as previous NEC editions identified it.