Protecting MC Cable - In Foam Roof

[fracasdan]

Hey Folks, this is my first post, so be gentle...

I'm wiring in lighting for an office building that has an open ceiling and my client doesn't want to look at any conduit on the ceiling. Since we are replacing the roof, anyway, we opted to run MC between the sheathing and the PVC roofing material. The inspector is saying that we can't do that, as the MC is not protect from any future nails/screws that may get sent through the roof.

I'm scratching my head for a solution that doesn't involve redoing all this work in EMT...

I'd love to access the hive mind on this one. Pic link below. Thanks!

https://imgur.com/a/ntBkkEI

 

[don_resqcapt19]

I don't think that the NEC directly address this installation, however if I was the AHJ, I would likely apply the last sentence of 300.4(E) and the exception and require rigid conduit. That sentence covers the installation of the wiring method the built up roof that is installed over metal corrugated sheeting. For the purposes of preventing damage to the wiring method, I don't see the fact that your roof is installed over wood sheeting making any difference. However, there is not a code section that I know of that covers this installation directly.

If you are under the 2020 code, I would also apply 330.80(C) that will require using the ampacity adjustment table for more than 3 current carrying conductors.

 

[hillbilly1]

Yeah, EMT wouldn’t fly either, but……you may be able to get a fab shop to build a metal nail guard over the entire MC runs. The inspector might let that fly. Don’t know how happy the roofers would be cutting out slots in the insulation to fit snugly over it.

 

[infinity]

I would be worried more about something penetrating the cables from underneath. I think that one could argue that this could be subject to physical damage.

 

[letgomywago]

I would be worried more about something penetrating the cables from underneath. I think that one could argue that this could be subject to physical damage.

If that's the case then anything run along the surface of any plywood wall in any situation would be subject to this. I think some sort of physical protection would be a good idea still since roofers then to be not to concerned with protecting electrical.

 

[AC\DC]

What section did he sight. If that’s just a membrain roof then their world be no screw and future is just that future, what if does not matter

 

[jmellc]

I think this would also count as a damp location and MC is not good for that. Plus, the 1 1/2 inch clearance to roof sort of comes into play here. Cable sandwiched between plywood and roof coating would be subject to nails and screws from anything someone installs on the roof. Or is the clearance 2 inches? I haven't had the issue lately and don't have my book handy.

 

[letgomywago]

I think this would also count as a damp location and MC is not good for that. Plus, the 1 1/2 inch clearance to roof sort of comes into play here. Cable sandwiched between plywood and roof coating would be subject to nails and screws from anything someone installs on the roof. Or is the clearance 2 inches? I haven't had the issue lately and don't have my book handy.

Mc is allowed in damp but not wet locations.

 

[MTW]

As an owner, I wouldn’t want to see that method either, best to ask your inspector what he would approve before reworking it again. I would want circuits installed spaced below the deck, like the code requires to prevent future roofers from driving screws through it.

Below the deck is much more accessible and visible than buried in the roof. One misplaced screw could be a nightmare to find and fix, with the way it’s installed now. Temperature would be more suitable underneath the deck as well.

 

[don_resqcapt19]

I think this would also count as a damp location and MC is not good for that. Plus, the 1 1/2 inch clearance to roof sort of comes into play here. Cable sandwiched between plywood and roof coating would be subject to nails and screws from anything someone installs on the roof. Or is the clearance 2 inches? I haven't had the issue lately and don't have my book handy.

As far as I know that rule only applies where you have a metal corrugated roof deck.

 

[jap]

Maybe cut the OSB out around the MC cables as you have it laid out on the roof and let it drop down on top of the bar joists and cover the top of them with a metal plate and let the roofers cover over the metal plate.

Wouldn't keep the mc from being visible from below, but, at least you wouldn't loose everything you've done up to this point.

Just my 2 cents worth.

JAP>

 

[fracasdan]

Thanks everyone. I just order 400' of 16 gauge galvi, cut in 6" strips to install as "Nail plates". My inspector is ok with that.

Thanks again,

 

[petersonra]

I have to wonder why someone thought this was a good idea in the first place. I don't see it as being especially subject to damage but I can't imagine the roofers went along with this.

IMO, best bet is rip it out and do something different. Maybe a chase on top of the roof (or under it)that the MC can be located in.