ECN Forum Forums Code Related Discussion NEC & other Code issues Bonding of metal siding

All I can say is building codes are tombstone documents. They usually get changed because somebody was killed (... or these days, some code panel member has a product they want to sell).

Yes, I've heard that said ... or, another variation, that the code is 'written in blood.' I'm not buying it. Nice rhetoric, but to imply that anything but the most aggressively expansive, "power of the pen" code application is akin to murder is simply irresponsible.

Codes, like all laws and all exercises of government authorty, are prescribed within limits- at least, in this country. The NEC itself recognizes this in its' introduction, where it speaks of the "practical" safeguarding of electricity.

We carry that through to the current example, where the code again limits its' application to 'likely' situations. Had the code panel wanted everything imaginable bonded, they would have said so.

Is there room for professionals to have differences of opinion in their judgement calls? Of course there is. That's why they're called 'professionals.'

If any code publisher wants to make the claim that theirs is a 'tombstone' document, I fully expect every sentence of code to be followed by the FPN "This line added in memory of Lotsa Sparks, whose untimely demise would have been avoided had only this change been in effect on March 32, 1874, when he was electricuted." Less specific than that, and it's just so much kant.

I guess the Florida rule for bonding steel studs could be called the Rafael Ugalde law.

When I posted this I didn't expect this much discussion~
Let me ask a couple other questions...
Has anyone seen a Listed method or product, technical reference, specification, engineering drawing, standard, or anything similar that details how to bond together perhaps several hundred individual pieces of siding or roofing such that you have can quantify the fault current carrying capacity? Say you are attempting to bond the siding and roofing of a large wood frame building. How many bonds are required and where do they have to be placed? If you bond only once in the area of the service is that adequate to clear a fault perhaps a couple hundred feet away in perimiter distance? What fault current is the design value? How about the case where it is a preexisting building and you don't know how the siding/roofing sections are joined or fastened?
Just curious.

I am not aware of any system specifically designed for this purpose.

The best I can think of is using a #10 bare copper wire, attached to the panels with the little spring clips that you sometimes see used on metal boxes; I hope they would grab the thinner metal.

For heavier metal, such as I-beams, I suppose a lug mounted to a beam clamp would work.

I say #10 for mechanical strength, and I'd run it inside, near the roof line for protection. I would not worry about a larger ampacity wire; #25 sheet metal can't carry all that many amps - any circuit larger than 30 amps is going to have to rely upon it's own ground wire.

We have a Lot of Pole buildings in our area. As some contain livestock ect we require the metal siding to be bonded. The usual Method is when the # 6 is run to the ground rod a Lug is fastened to the siding and that wire run thur the lug on the way to the grounding Electroid.
We do not require each individual sheet of siding to get a connection. We've found that to work quite well. If you want to comment on this renosteinke please make it a Polite and Possibly Constructive comment. I;ve been in the Trade over 45 yrs & formally carried Masters licenses in nine states I feel I;ve earned that!!
Thank you

Yoop:
FWIW, the method you describe above would be OK in my opinion as an inspector. Alum. siding is not very prevanant here (NJ), but I have run accross a few metal skin structures lately. Where the 'skin' mechanical connection to the metal framing was compromised, lugs and #6 were installed. I commented earlier (page 1) as to my opinion, and I'll stick with that comment also.

I don't see any general requirement to bond the metal siding, roofing, or incidental structural steel in the NEC. Indeed, by saying 'likely to become energized' the NEC seems pretty clear in saying "no need to bond."

Granted, that's a general requirement. Other parts of the NEC -pool areas and some agricultural buildings being examples- the NEC has another requirement that all metal be bonded. Those are special circumstances, and the requirement is limited to them.

I am curious: where do we get the #6 requirement? After all, we're not talking about the water bond - where the incoming water pipe might also become a grounding electrode.

# 6 Came from 250.66 (A) as the wires going to A rod.
Yoopersup

Reno:
What I said above was a 'spec' by the project engineer & architect for that structure. BTW, commercial garage, maintenance shop for a gov't branch.

Basically, if the EE/PE/Arch specs 3/0 Cu to 10' x 3/4" rods, 25' apart in a triangle, that's what they get. No, it's not NEC required. & I don't believe I said that anywhere.