Does a metal tin ceiling have to be bonded?

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brantmacga

brantmacga

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I’m working on a cook shed for a friend; the ceiling is tin with recessed lighting.

He told me today the inspector had mentioned something about bonding the tin.

Is there an NEC requirement for this?

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You have 250.4(A)(4)

(4) Bonding of Electrically Conductive Materials and Other Equipment. Normally non–current-carrying electrically conductive materials that are likely to become energized shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path
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The sheets have to be

* connected together - they're connected at the seam, so that's covered

* connected to the electrical supply source - I could see this going either way ... if the sheets are on the top of the rafters, they could be floating and need a jumper somewhere to something bonded. If you had roof sheets screwed into the top of bar joist type trusses, and electrical conduits and boxes bolted to the trusses, I would think that's a good bond.

* in a manner that establishes an effective ground fault current path - this seems subjective, are the seams a good enough bond? If you have overlapping sheets of bare galvanized corrugated tin, that seems like a very good electrical connection, if the sheets are epoxy coated and the screws are coated with some climate seal, maybe not.
 
low-wattage said:
You have 250.4(A)(4)



The sheets have to be

* connected together - they're connected at the seam, so that's covered

* connected to the electrical supply source - I could see this going either way ... if the sheets are on the top of the rafters, they could be floating and need a jumper somewhere to something bonded. If you had roof sheets screwed into the top of bar joist type trusses, and electrical conduits and boxes bolted to the trusses, I would think that's a good bond.

* in a manner that establishes an effective ground fault current path - this seems subjective, are the seams a good enough bond? If you have overlapping sheets of bare galvanized corrugated tin, that seems like a very good electrical connection, if the sheets are epoxy coated and the screws are coated with some climate seal, maybe not.
Click to expand...


:unsure:

JAP
 
So every metal roof on a building with electricity has to be bonded??
I haven’t ever bonded a metal roof on a house. Doubt many others have either.
 
Hv&Lv said:
So every metal roof on a building with electricity has to be bonded??
I haven’t ever bonded a metal roof on a house. Doubt many others have either.
Click to expand...
It seems like something that someone forgot about. Maybe someone should suggest a change to the code to require metal roofing and siding to be bonded to the GES with a #6 conductor. :)
 
low-wattage said:
You have 250.4(A)(4)



The sheets have to be

* connected together - they're connected at the seam, so that's covered

* connected to the electrical supply source - I could see this going either way ... if the sheets are on the top of the rafters, they could be floating and need a jumper somewhere to something bonded. If you had roof sheets screwed into the top of bar joist type trusses, and electrical conduits and boxes bolted to the trusses, I would think that's a good bond.

* in a manner that establishes an effective ground fault current path - this seems subjective, are the seams a good enough bond? If you have overlapping sheets of bare galvanized corrugated tin, that seems like a very good electrical connection, if the sheets are epoxy coated and the screws are coated with some climate seal, maybe not.
Click to expand...
Well, here they clearly aren't, unless they are cleverly disguising metal bars joists as wooden roof joists.
 
low-wattage said:
You have 250.4(A)(4)



The sheets have to be

* connected together - they're connected at the seam, so that's covered

* connected to the electrical supply source - I could see this going either way ... if the sheets are on the top of the rafters, they could be floating and need a jumper somewhere to something bonded. If you had roof sheets screwed into the top of bar joist type trusses, and electrical conduits and boxes bolted to the trusses, I would think that's a good bond.

* in a manner that establishes an effective ground fault current path - this seems subjective, are the seams a good enough bond? If you have overlapping sheets of bare galvanized corrugated tin, that seems like a very good electrical connection, if the sheets are epoxy coated and the screws are coated with some climate seal, maybe not.
Click to expand...

I appreciate you finding this code to discuss.

Reading this, it seems to me the EGC to the fixture would provide the path to ground in case of a fault. My interpretation would be that this ceiling isn’t likely to become energized by something other than the fixtures, which again, are grounded.

Any thoughts on that?


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Check the local building code . In Ohio the OBC has a requirement in the electrical section to bond metal veneer on structures.
 
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