Conduit or Cable Near Roof Deck

[Little Bill]

Had a fellow electrician call and was explaining how he was going to wire a metal building with a metal roof, inside and out.
I was trying to tell him that you had to stay so far away from the deck on a metal roof. I've had a brain malfunction and can't find the code article on that. A little help please!

 

[texie]

300.4(E)

 

[Little Bill]

300.4(E)

Thanks!
I was all over 300 and kept glancing over that!

 

[Little Bill]

If you had a roof that had metal on top of rafters and also under the rafters on the inside, would 300.4(E) apply?

 

[texie]

If you had a roof that had metal on top of rafters and also under the rafters on the inside, would 300.4(E) apply?

Not in my view. The metal on the bottom side is not the roof deck.

 

[kwired]

If you had a roof that had metal on top of rafters and also under the rafters on the inside, would 300.4(E) apply?

Read the informational note. Yes it is not part of code but does help explain the intent of the rule.

That said there possibly room for interpretation differences here but I am assuming the main intent was to not fasten wiring methods to underside of metal decking that gets insulation board and/or waterproof membrane fastened to the top side, the fasteners they use for those have possiblity of penetrating the wiring method, even sometime down the road when the roof needs redone. I don't think it was intended to apply to a roofing method where the sheet metal panel is the finished exterior surface like on many "pole barns" or similar build structures.

 

[Little Bill]

This is the roof in question.

 

[jusme123]

Thats a ceiling, not a roof.

 

[texie]

Thats a ceiling, not a roof.

My point exactly. Obviously the intent of the rule is so that tek screws used to fasten the roof deck don't poke through and into a cable or raceway. A raceway on this ceiling won't be anywhere near the screws attaching the roof decking.
But I'm sure there will be some clueless inspector out there, that the week before was selling ladies shoes, that will say it is a violation.

 

[hillbilly1]

We get a lot of calls replacing conduit and wire on buildings built before that rule went into affect. When they re-roof flat roofs, they usually add another layer of insulation and use long a** screws to reach the old decking. If the conduit is run in the V, it gets hit quite often. The black spots on the ceiling is the telling sign along with all the tripped breakers. I was tasked with inventing something to locate the runs under the decking, and mark it up top. Never did come up with anything practical.

 

[jusme123]

Is FA conduit allowed to be mounted to the roof deck?

 

[acrwc10]

We get a lot of calls replacing conduit and wire on buildings built before that rule went into affect. When they re-roof flat roofs, they usually add another layer of insulation and use long a** screws to reach the old decking. If the conduit is run in the V, it gets hit quite often. The black spots on the ceiling is the telling sign along with all the tripped breakers. I was tasked with inventing something to locate the runs under the decking, and mark it up top. Never did come up with anything practical.

Even if you had invented something and marked the roof above the conduit it orange paint, someone would think that is where you put the longest screws! It’s a test.

 

[kwired]

Is FA conduit allowed to be mounted to the roof deck?

I'd say no, but at same time because they typically are "supervised circuits" that are run in them, you would at least get a trouble indication if something does happen to the contained circuit(s).

 

[don_resqcapt19]

Is FA conduit allowed to be mounted to the roof deck?

Prior to the 2020 code the NEC did not prohibit that. 760.3 says that only those sections of Article 300 that are specifically cited in Article 760 apply to fire alarm system installations. In the 2017 code, the reference in 760.24(A) was only to 300.4(D).
The under roof decking rule is in 300.4(E).

In the 2020 code the reference in 760.24(A) is too all of 300.4.