NEC 344.14...Stainless Steel RMC and fittings...Again

[Student_Pete]

Greetings. I have read a previous post on the reason for NEC 344.14 requiring only stainless steel fittings on stainless steel RMC. None of the responses address the following situation: on certain secure facilities we would use RMC as a tamper-resistant carrier, then put in a dielectric brake - simply a Schedule 80 PVC adapter - then resume RMC when traversing certain boundaries.

Supposing the RMC is stainless, why is this not permissible by 344.14? It makes sense to prohibit dissimilar metal fittings, but what about PVC? No galvanic action possible. In fact, 344.14 is titled: Dissimilar Metals. But then it says:

"Stainless steel rigid conduit shall only be used with the following:

(1) Stainless steel fittings"

And no exception for nonmetallic fittings.

I'm brand new to the forum and somewhat new to the NEC, so I apologize if there is some other thread or NEC clause I missed concerning this.

 

[gadfly56]

Greetings. I have read a previous post on the reason for NEC 344.14 requiring only stainless steel fittings on stainless steel RMC. None of the responses address the following situation: on certain secure facilities we would use RMC as a tamper-resistant carrier, then put in a dielectric brake - simply a Schedule 80 PVC adapter - then resume RMC when traversing certain boundaries.

Supposing the RMC is stainless, why is this not permissible by 344.14? It makes sense to prohibit dissimilar metal fittings, but what about PVC? No galvanic action possible. In fact, 344.14 is titled: Dissimilar Metals. But then it says:

"Stainless steel rigid conduit shall only be used with the following:

(1) Stainless steel fittings"

And no exception for nonmetallic fittings.

I'm brand new to the forum and somewhat new to the NEC, so I apologize if there is some other thread or NEC clause I missed concerning this.

I'm guessing you're talking about SCIF's. The feds are an island unto themselves when it comes to the code. They may choose to modify the national standards as they see fit to meet the facility's requirements. The important thing is to make sure that you get such exceptions in writing, because the folks who do the drawings inevitably pepper them with clauses about "code compliant installation" and "latest standards" and what not.

 

[Student_Pete]

I'm guessing you're talking about SCIF's. The feds are an island unto themselves when it comes to the code. They may choose to modify the national standards as they see fit to meet the facility's requirements. The important thing is to make sure that you get such exceptions in writing, because the folks who do the drawings inevitably pepper them with clauses about "code compliant installation" and "latest standards" and what not.

Thank you for the reply. Yes, originally I had this done in SCIFs where RMC was carrying low power signal cables - a "Protected Distribution System." But why can this not be done with normal 240/120 wiring? I'm interested in why nonmetallic fittings are not allowed. Thank you again for the reply.

 

[electrofelon]

I'm interested in why nonmetallic fittings are not allowed. Thank you again for the reply.

One could argue that because the title of 344.14 is "dissimilar metals", only metal fittings are part of the restriction.