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Bonding of metal siding #190126 11/07/09 09:57 AM
Joined: Jul 2002
Posts: 103
jes Offline OP
Is anyone aware of a requirement in the NEC or any local code (this is in New England) to bond the metal siding and roofing of a wood framed building to the grounding electrode system of the building?

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Re: Bonding of metal siding [Re: jes] #190139 11/07/09 03:07 PM
Joined: Nov 2007
Posts: 763
KJay Offline
Generally no. The closest thing I can find in the NEC to mentioning this is the FPN to 250.116.
I don’t see anything the MA Amendments either, but you may have some additional local requirements where you are.
Likely to become energized wouldn’t seem to hold much weight here IMO, unless maybe you have electrical equipment attached directly to the surface.

However, if there where a pool or hot tub within 5-feet then IMO, the bonding requirements of 680.26,B [7] and/or possibly 680.43, [4] would apply for the metal siding and gutter downspouts, etc… but probably not the metal roofing itself, at least if it’s over 12-feet above the max water level.

Re: Bonding of metal siding [Re: KJay] #190142 11/07/09 04:16 PM
Joined: Jul 2004
Posts: 9,575
gfretwell Offline
The real question is whether it is "likely to become energized" and then you bond it to the EGC of the circuit likely to energize it.
The interpretation I have seen is when you have a penetration for an outside light or receptacle, you be sure the EGC to box grounds the metal sheathing. Since that can't be a sheet metal screw it might be a little more complicated than just screwing the box on it.

Greg Fretwell
Re: Bonding of metal siding [Re: gfretwell] #190179 11/08/09 05:32 AM
Joined: Nov 2007
Posts: 763
KJay Offline
I really don’t want to pick a fight with the IAEI, but IMO, if the electrical equipment and wiring attached to the metal siding is properly installed, then "likely to become energized" is for all intents and purposes, a moot point.
The listed equipment, boxes and enclosures that are mounted directly to the siding, when properly installed in accordance the NEC and the manufacturers listed instructions, are bonded to the equipment-grounding conductor of the branch circuit or circuits likely to energize it through listed means, meaning grounding screws, lugs, etc.

All of the shock hazards that I have seen or heard of where energized metal siding was involved, were the direct result of either improper installation or a screw being driven into a wire inside a wall that was not part of a circuit likely to energize the metal siding.

Re: Bonding of metal siding [Re: KJay] #190183 11/08/09 01:41 PM
Joined: Jul 2004
Posts: 9,575
gfretwell Offline
The point is, even if the bonding was only a 14 ga, it would still operate an overcurrent device unless we were talking about a big feeder.
Florida is pretty serious about bonding since we are the ones who killed an appliance installer with energized steel studs and we have had problems with energized siding. Usually a metal box, securely attached to the metal siding, will accomplish this.
If this is a metal building it is a slam dunk 250.104(C)

Greg Fretwell
Re: Bonding of metal siding [Re: gfretwell] #190190 11/08/09 08:36 PM
Joined: Nov 2007
Posts: 763
KJay Offline
The only thing I wonder about though, with wafer thin resi siding… is if you could actually get the two-thread engagement required to mount a lug on it.
Seems that tearing of the siding might be a potential problem when using a nut and bolt to securing a lug somewhere down at the bottom of the first course panels.

I guess if they are considering the siding panels as the "structural frame" of the building, then 250.104[C] would apply. If they are having issues in the area, I don’t see how it could hurt to bond them.
In my area, usually the steel building frame itself is bonded and the siding panels are coincidentally bonded through the screws used to fasten the panels to the metal building frame.

Re: Bonding of metal siding [Re: KJay] #190199 11/08/09 10:10 PM
Joined: Jan 2005
Posts: 5,316
renosteinke Offline
Cat Servant
Please, please, please ... don't open that can of worms, KJ!

If you do, someone is sure to notice that the entire building is assembled using sheet metal screws, and will want a 'proper' lug and jumper between each and every piece that makes up the building! frown

Re: Bonding of metal siding [Re: KJay] #190201 11/08/09 10:15 PM
Joined: Apr 2002
Posts: 7,237
HotLine1 Offline
A utility meter surface mounted to the structure could also be a 'bonding' point; neutral bonded to meter pan, meter pan screwed to/thru al. siding?

Should we not consider that the service entrance conductors are the largest conductor/circuit that may energize the siding?

With 2008, 250.94, another optional bonding point? Depending upon the mfg of the 250.94 termination device, IF it's screwed to.thru the siding?

As to getting a 'two thread' tap for a lug, I really don't see that happening. WE have bonded al. downspouts, installing lugs (rivited).

Re: Bonding of metal siding [Re: HotLine1] #190221 11/09/09 10:58 AM
Joined: Feb 2002
Posts: 2,233
harold endean Offline
I have seen an electrical job where the EC bonded the metal siding of the house to the hot tub because it was close enough to touch. He wanted to be safe and bond the 2 together.

Re: Bonding of metal siding [Re: harold endean] #190232 11/09/09 04:08 PM
Joined: Jul 2004
Posts: 9,575
gfretwell Offline
If you have metal siding near the pool/spa it must be bonded along with screen cages, window frames or whatever, just like the ladder.
There was a lot of confusion about this sheet metal screw thing but I think that really only applies to how you fasten a lug or bond wire, not the connection of each piece.

In Florida there are not a lot of "siding" houses, at least not here but you do see it a lot in trailers and they use aluminum gable ends and soffit. The meter pan is as likely to be against block as anything and in a trailer it is in a post.

Again, a while ago, when the Prodigy SS guys were talking a lot I did an experiment and found my Ecos ground tester was happy with the incidental bonding between the gable ends at each end of my house (42') merely by the soffit between them.
The exhaust fan on one end effectively bonded that side and a test from the HVAC service outlet on the other end to the gable showed <1 ohm under load. (the Ecos test parameter)
If you made an effort to connect any metal you penetrated to the circuit you penetrated it with, I think you are good to go. Usually the box is mounted right on that metal (much liker John's meter can example).
I would want to see something more substantial with a pool/spa tho. I do believe if you get one piece, the way aluminum siding snaps together, you have them all.

Greg Fretwell
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