There was a recent electrocution in NH as the result of a screw being driven thru a new flat roof deck and into an MC cable. The cable had been installed through the space that is formed between a corrugated steel roof deck and the top of a steel roof joist. Article 330.17 refers us back to Article 300.4. Article 300.4 addresses a number of conditions, but does not appear to address this particular routing location. Does anyone read something that does not allow this installation method?
MC cable above roof joists
- Thread starter bdingman
- Start date
- Status
- Location
- Massachusetts
Re: MC cable above roof joists
This is a very common installation method in this area.
I have been at it 20+ years and have never heard of this being a violation.
Even if you could say that this MC cable required "nail plate" protection, these plates are only 1/16" inch thick.
The steel truss they are trying to drive a Tek screw into is thicker than 1/16", they would never notice the "nail plate" and would drive right through it.
This is a very common installation method in this area.
I have been at it 20+ years and have never heard of this being a violation.
Even if you could say that this MC cable required "nail plate" protection, these plates are only 1/16" inch thick.
The steel truss they are trying to drive a Tek screw into is thicker than 1/16", they would never notice the "nail plate" and would drive right through it.
fishin' electrician
Senior Member
- Location
- Connecticut
Re: MC cable above roof joists
I'm with Bob on this one. I just replaced 50' of 1" EMT on a remodel because there was a 4" tek screw into the pipe every 4' or so. If the EMT won't stop it, neither would a nail plate. The roofer must have done it after the install of the original conductors and got lucky. We only found it because after removing the old TW, the THHN wouldn't pull in. I always double check where I'm drilling or screwing, why can't the roofers? :roll:
I'm with Bob on this one. I just replaced 50' of 1" EMT on a remodel because there was a 4" tek screw into the pipe every 4' or so. If the EMT won't stop it, neither would a nail plate. The roofer must have done it after the install of the original conductors and got lucky. We only found it because after removing the old TW, the THHN wouldn't pull in. I always double check where I'm drilling or screwing, why can't the roofers? :roll:
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
Re: MC cable above roof joists
There was a recent electrocution in NH as the result of a screw being driven thru a new flat roof deck and into an MC cable.
I want to know how there was an electrocution. If the MC was properly installed, driving a screw into it should have caused the overcurrent device to trip due to (at a minimum) an armor to hot fault. Little voltage should have been present on that screw, especially if the steel roof deck were properly grounded also.
Sounds like people screwed up here and it wasn't the roofer.
Hal
[ February 19, 2004, 05:34 PM: Message edited by: hbiss ]
There was a recent electrocution in NH as the result of a screw being driven thru a new flat roof deck and into an MC cable.
I want to know how there was an electrocution. If the MC was properly installed, driving a screw into it should have caused the overcurrent device to trip due to (at a minimum) an armor to hot fault. Little voltage should have been present on that screw, especially if the steel roof deck were properly grounded also.
Sounds like people screwed up here and it wasn't the roofer.
Hal
[ February 19, 2004, 05:34 PM: Message edited by: hbiss ]
- Location
- Massachusetts
Re: MC cable above roof joists
I was wondering the same thing Hal.
Almost imposable to imagine steel roof decking being screwed to steel truss that was isolated.
I was wondering the same thing Hal.
Almost imposable to imagine steel roof decking being screwed to steel truss that was isolated.
tonyi
Senior Member
Re: MC cable above roof joists
I suspect (spiral) MC armor, lacking AC's bond wire, could easily have too much resistance over a long span for a breaker to trip. This is not unlike the scenario that allows old BX to get glowing hot without tripping a breaker.
If the building steel were grounded, that could shorten up the fault path some, but then again, if the stuff had been there for a while and was AL armor, AL Oxide is not a good conductor...and the joists were probably covered with paint...
This is one of the things about MC that has always bugged me - a lot of people want to diss AC, but this is one failure mode AC doesn't have
[ February 19, 2004, 06:43 PM: Message edited by: tonyi ]
I suspect (spiral) MC armor, lacking AC's bond wire, could easily have too much resistance over a long span for a breaker to trip. This is not unlike the scenario that allows old BX to get glowing hot without tripping a breaker.
If the building steel were grounded, that could shorten up the fault path some, but then again, if the stuff had been there for a while and was AL armor, AL Oxide is not a good conductor...and the joists were probably covered with paint...
This is one of the things about MC that has always bugged me - a lot of people want to diss AC, but this is one failure mode AC doesn't have
[ February 19, 2004, 06:43 PM: Message edited by: tonyi ]
- Location
- Massachusetts
Re: MC cable above roof joists
Tony putting aside the fault path of the MC armor I am still curious as to how this screw was not 'grounded' by the steel deck it passed through.
I have never seen a fault to building steel not clear a breaker.
Obviously it did not clear it this time and I would like to know why and how.
Tony putting aside the fault path of the MC armor I am still curious as to how this screw was not 'grounded' by the steel deck it passed through.
I have never seen a fault to building steel not clear a breaker.
Obviously it did not clear it this time and I would like to know why and how.
Re: MC cable above roof joists
This is not meant to change the point at hand, or whether this was indeed the cause, but who did the investigation and came up with this being the cause?
Tony, I could maybe see your argument in a wooden structure with a metal roof, but in any case, there are better odds of this scenario opening an OCPD than the odds that it wouldn't open the device.
This is most likely a commercial structure, so unlike residential, there are many more applications involving other trades that help gaurantee bonding even if not intended.
Roger
This is not meant to change the point at hand, or whether this was indeed the cause, but who did the investigation and came up with this being the cause?
Tony, I could maybe see your argument in a wooden structure with a metal roof, but in any case, there are better odds of this scenario opening an OCPD than the odds that it wouldn't open the device.
This is most likely a commercial structure, so unlike residential, there are many more applications involving other trades that help gaurantee bonding even if not intended.
Roger
Re: MC cable above roof joists
One of our State Electrical Inspectors saw the cable routing while inspecting at a NH high school renovation that my firm did the MEP engineering on. He mentioned the electrocution to the construction manager. The CM put it in a memo that he sent to the electrical contractor and copied us. I haven't talked to inspector yet, but hope to catch up with him tomorrow. I'll get the specifics then and let you guys know.
I'm still looking to know if anyone can help with the code issue. The owner is asking whether the EC has to move the cables because of a code article or if the owner would have to pay to have them moved. I don't believe there is an article that won't allow this installation. I've seen MC and EMT installed this was many times also.
I'll post some info after I talk to the inspector. Thanks
One of our State Electrical Inspectors saw the cable routing while inspecting at a NH high school renovation that my firm did the MEP engineering on. He mentioned the electrocution to the construction manager. The CM put it in a memo that he sent to the electrical contractor and copied us. I haven't talked to inspector yet, but hope to catch up with him tomorrow. I'll get the specifics then and let you guys know.
I'm still looking to know if anyone can help with the code issue. The owner is asking whether the EC has to move the cables because of a code article or if the owner would have to pay to have them moved. I don't believe there is an article that won't allow this installation. I've seen MC and EMT installed this was many times also.
I'll post some info after I talk to the inspector. Thanks
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
Re: MC cable above roof joists
As far as I can see there is nothing in the code that would prohibit running cables or conduits there. If the owner wants them moved it's up to him and he will have to foot the bill.
Hal
As far as I can see there is nothing in the code that would prohibit running cables or conduits there. If the owner wants them moved it's up to him and he will have to foot the bill.
Hal
Re: MC cable above roof joists
Bdingman, as Hal states, there is no specific wording that prohibits this installation and if you go back to Iwire's first post, it is not only a "very common installation method in this (his) area"' it is also common here in the south.
I think there may be some speculation involved, but that is only my oppinion and nothing else.
Back to the code, with the exception of the vague wording of 110.3(8), I don't think there is a code argument.
I think this may be an issue for a 2008 ROP given that this has come up before.
Roger
Bdingman, as Hal states, there is no specific wording that prohibits this installation and if you go back to Iwire's first post, it is not only a "very common installation method in this (his) area"' it is also common here in the south.
I think there may be some speculation involved, but that is only my oppinion and nothing else.
Back to the code, with the exception of the vague wording of 110.3(8), I don't think there is a code argument.
I think this may be an issue for a 2008 ROP given that this has come up before.
Roger
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: MC cable above roof joists
This kind of go with the problem of other trades not checking where equipment installed by other trades might be. Another good point to this would be if this owner tries to say it's the electrican's fault for having the cable there then what about when a plumber core drills through a concrete slab through a RMC conduit. or when a sider drives a nail through the back of a service panel. I think other trades have to be aware that when they are doing work that requires penetration into a structure they need to contact other trades to let them know if they have equipment in there. Or get off their backsides and check for them selfs.
This kind of go with the problem of other trades not checking where equipment installed by other trades might be. Another good point to this would be if this owner tries to say it's the electrican's fault for having the cable there then what about when a plumber core drills through a concrete slab through a RMC conduit. or when a sider drives a nail through the back of a service panel. I think other trades have to be aware that when they are doing work that requires penetration into a structure they need to contact other trades to let them know if they have equipment in there. Or get off their backsides and check for them selfs.
luke warmwater
Senior Member
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