Bonding a metal roof

[Bad Habit]

So, had a metal roof installed on our manufactured home. The State of WA, Department of Labor and Industries controls everything associated with Manufactured and Mobile Homes, along with all Electrical in the state. Seems they want to make sure every aspect of these structures is over scrutinized and regulated.

They require the roof to be bonded in 2 places, opposite corners of the structure down to the frame of the home. As I'm not really sure what the best way to attach a bonding wire (#8 min) to a tin can, I called the manufacturer (based here in WA) and asked them. They sort of chuckled and said they scratch their head about it too and didn't have any official info but gave me some ideas. So, I ended up with a crimped lugs, bolted through the seams, using paint piercing star washers at 2 places. Then brought these 2 bonding wires down and attached them to the service ground. I didn't attach them at the far corners however, I attached them under the ridge cap and ran the wire for the far one under the cap to keep it nice and tidy.

So, the inspector failed it. Because they apparently do inspections at random times, after some indeterminate amount of calendar days after the inspection request(s), no one was there at the time. I'm hoping he just didn't see what he expected to see and thought nothing was done, or maybe it's just got to be done the way he thinks it should be.

Anybody here have any experience with bonding a metal roof? No solar or power up there of any kind. Haven't seen anything saying why it would be a requirement other than the State saying it is.

 

[sberry]

2 reasons, lightning and short circuit. Any steel that has any potential to be energized should be grounded.

 

[Bad Habit]

So, why don't traditional stick built homes require the roof to be bonded? Why isn't there more info on, and options for, attaching to the roof panels? I would have thought that steel roofing manufacturers would be happy to overcharge for some sort of device, but they don't have anything.

 

[tyme2par4]

We've been dealing with this in the solar industry for years now. There really is no effective way to bond thin gauge metal like that. I've tested some of the snow retention clamps, and on some roof types, they do bond to the roofing, but I can't guarantee all work. There are just way too many types to test everything.
With the latest code, there is an exception for grounding metal roofing under solar panels. Is it the right thing to do? I don't know. But no one wanted to take ownership of it.

 

[Bad Habit]

So, for anyone following along. The requirement comes from HUD: (still no idea how to attach)

LII Electronic Code of Federal Regulations (e-CFR) Title 24. Housing and Urban Development Subtitle B. Regulations Relating to Housing and Urban Development Chapter **. OFFICE OF ASSISTANT SECRETARY FOR HOUSING - FEDERAL HOUSING COMMISSIONER, DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT Part 3280. MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS Subpart I. Electrical Systems Section 3280.809. Grounding.

(d)Bonding of noncurrent-carrying metal parts.

(1) All exposed noncurrent-carrying metal parts that may become energized shall be effectively bonded to the grounding terminal or enclosure of the distribution panelboard. A bonding conductor shall be connected between each distribution panelboard and an accessible terminal on the chassis.

(2) Grounding terminals shall be of the solderless type and approved as pressure-terminal connectors recognized for the wire size used. Star washers or other approved paint-penetrating fitting shall be used to bond terminals to chassis or other coated areas. The bonding conductor shall be solid or stranded, insulated or bare and shall be No. 8 copper minimum, or equal. The bonding conductor shall be routed so as not to be exposed to physical damage. Protection can be afforded by the configuration of the chassis.

(3) Metallic gas, water and waste pipes and metallic air-circulating ducts shall be considered bonded if they are connected to the terminal on the chassis (see § 3280.809) by clamps, solderless connectors, or by suitable grounding-type straps.

(4) Any metallic roof and exterior covering shall be considered bonded if (i) the metal panels overlap one another and are securely attached to the wood or metal frame parts by metallic fasteners, and (ii) if the lower panel of the metallic exterior covering is secured by metallic fasteners at a cross member of the chassis by two metal straps per manufactured home unit or section at opposite ends. The bonding strap material shall be a minimum of 4 inches in width of material equivalent to the skin or a material of equal or better electrical conductivity. The straps shall be fastened with paint-penetrating fittings (such as screws and star washers or equivalent).
[40 FR 58752, Dec. 18, 1975. Redesignated at 44 FR 20679, Apr. 6, 1979, as amended at 58 FR 55020, Oct. 25, 1993]

 

[tyme2par4]

Well by that definition it would appear that the roof is considered bonding if you use metal screws to fasten it...
Using a compression lug with a star washer as you mentioned earlier should be acceptable as well.

 

[sberry]

Most of the issues with sheet and roof are not extremely high current and long duration, a fault from 120V is fast and lightning while hi voltage is low current for lack of better wording and my rudimentary understanding. This is not a current carrying conductor similar to service entrance wire. Only needs to work in a short event.

 

[Stuart in MN]

So, for anyone following along. The requirement comes from HUD:

That's pretty much word for word what the NEC codebook says.

 

[Old Man Roger]

Sorry if it's been suggested already, maybe ask the guy doing the inspection what he wants?

 

[mm08822]

That's pretty much word for word what the NEC codebook says.

NEC does not require building sheet metal to be bonded, only the structural members that create the building frame if so constructed with. 250.104C

 

[mm08822]

Sorry if it's been suggested already, maybe ask the guy doing the inspection what he wants?

Agreed, find out why it failed first before doing anything further.

 

[JoeMcGov]

I've done millions and millions of square feet of metal roofs on commercial buildings, mostly huge storage warehouses. I don't ever recall having to "bond" the roof as part of the design.

 

[Max]

A “typical” lightning hit is 10,000 to 200,000 Amps. That #8 wire will be plasma. I don’t really see any benefit to the bonding for lightning. I suppose if the roof picks up a charge from the wind, etc. that the wire will ground it.

Completely agree on NOT having an energized roof. So to me the NEC need is good enough...

We had a metal roof installed on our old house in the SF Bay Area. Surprisingly for CA, there were no reqts for grounding.

Max

 

[Bad Habit]

Trust me, I'm trying to find out what the inspector would like to see. They're "supposed" to be available for calls at their desk between 8 and 8:30. So far it appears that doesn't mean they have to answer the calls. Have a couple of messages asking about it, explaining how i did bond it and asking for a call back but do far nothing. For now trying not to be a pest, but it take 2 trips to the office to get him out to inspect,and even then it was a week and a half later.

Whatever he wants to see I'll do, but want to know what that is before I start redoing and adding things. As no one I've run across has had to deal with this I don't have reference point

Sent from my Pixel 2 XL using Tapatalk

 

[Leaflessshadetree]

Any chance you can look at other buildings (presumably approved) in the area?

 

[Stuart in MN]

NEC does not require building sheet metal to be bonded, only the structural members that create the building frame if so constructed with. 250.104C

Look at article 550.16 under manufactured homes. Paragraph(4) in post #5 above is essentially word for word the same text.

 

[mm08822]

Look at article 550.16 under manufactured homes. Paragraph(4) in post #5 above is essentially word for word the same text.

Agreed, 550.16 trumps 250.104C. A garage/outbuilding is not a manufactured home!

OP, Fine print note in NEC 550 states HUD adopted many articles in NEC 550.

Either way, NEC or HUD requires it. Make the call. Find out why inspector failed you.

 

[sberry]

I've done millions and millions of square feet of metal roofs on commercial buildings, mostly huge storage warehouses. I don't ever recall having to "bond" the roof as part of the design.

They are already bonded thru building steel.

A “typical” lightning hit is 10,000 to 200,000 Amps. That #8 wire will be plasma. I don’t really see any benefit to the bonding for lightning. I suppose if the roof picks up a charge from the wind, etc. that the wire will ground it.

It seems I don't know wtf,,, I just ask my tech, he agrees with you that a direct hit would fry the wire.

 

[Bad Habit]

I think why there are so few examples to gather info from is that not many people retro fit a manufactured or mobile home with a metal roof. It maybe one thing if they come from the "factory" with one (where they would have bonding straps built in and inspected), but going back and adding it isn't as common. The home is in a high fire danger area and I wanted to have a little more comfortable feeling. It was worth the extra expense to me, and I needed to replace the roof anyway.

I don't feel lightning is the driving force for this, but could see static build up being an issue with wind, and then making it more susceptible to lightning strikes. And of course the general bonding of metallic elements. Does make you wonder why traditional built homes don't have the requirement. I guess beyond the UBC, the feds don't get involved in construction practices to that level, it's all local and/or state.

 

[Bad Habit]

OK, finally got a call back from the inspector. He's allowing me to leave the connection points at the top under the ridge cap, technically they are supposed to be out at the corners but he agreed that everything is bonded and being under the cap, it's better protected. I do have to move the other end from the service ground wire to the frame of the home, easy enough. Having not paid attention in my enjoyable forays crawling around under there, I never noticed a specific bond from the frame to the service or other ground, but I would assume it's there. Luckily the snow has melted enough that I can get under there now.

 

[greg13]

Manufactured homes are subject to a bunch of "odd" regulations that traditional stick built homes are exempt from, such as outside air intakes for heating appliances. Most manufactured homes leak air so bad that you could never deplete the oxygen!

 

[sberry]

I know it isn't the roof but lots of these homes have steel frames and some.metal x bracing. They call for a frame bond.

 

[ard]

(1) All exposed noncurrent-carrying metal parts that may become energized shall be effectively bonded to the grounding termina

The key is 'that may become energized'


Does the inspector have a theory on how the roof will get energized?

THis has come up before with metal siding. Not unique to mfg buildings...more unique to idiot inspectors.