PVC boxes allowed on hot roof?

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Coppersmith

Coppersmith

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Location
Tampa, FL, USA
Occupation
Electrical Contractor
I'm running EMT on a flat metal standing seam roof. I need 3R 12x12 and 8x8 junction boxes up there but there doesn't seem to be any metal ones made for this purpose. There's plenty of 3R metal boxes to mount on walls, but I want ones that lay flat with a top that comes off or is hinged.

I've talked to several supply houses who all say everybody uses PVC boxes. Is this true? I'm not allowed to run PVC pipe on the roof because ambient temp will exceed 122 degrees. Seems like a PVC box would be just as likely to melt or deform.
 
If it helps, Carlon has the following: These UL approved and CSA recognized enclosures also withstand wet and dirty environments, while their thick wall construction and temperature range (from -40° F to 185° F)

You might also consider 314.3. Depending on the size of your EMT you will likely not be able to install boning means.
 
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augie47 said:
You might also consider 314.3. Depending on the size of your EMT you will likely not be able to install boning means.
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That is an issue. With 2" and 1.5" Myers hubs there are two threads left for the bonding bushing. The 3/4" has no threads left. I was thinking of using pipe ground clamps on the pipes outside the box and bonding that way. Not compliant to 314.3 but the best I can do unless someone makes hubs with integral ground lugs.
 
Coppersmith said:
I'm running EMT on a flat metal standing seam roof. I need 3R 12x12 and 8x8 junction boxes up there but there doesn't seem to be any metal ones made for this purpose. There's plenty of 3R metal boxes to mount on walls, but I want ones that lay flat with a top that comes off or is hinged.

I've talked to several supply houses who all say everybody uses PVC boxes. Is this true? I'm not allowed to run PVC pipe on the roof because ambient temp will exceed 122 degrees. Seems like a PVC box would be just as likely to melt or deform.
Click to expand...

Look up this NEMA 3R 12 x 12 x 6 enclosure from cooper 12126SCG
 
We use PVC boxes as Jboxes on solar arrays. I forgot about the temperature rating requirement for PVC conduit ... but does it even apply to boxes? We've had no problems so far.

I kinda hate to admit it, but we just thread grounding bushings onto rainright connectors with no locknuts. Seems just as sufficient mechanically. Haven't failed an inspection yet. (Where is the code section that prohibits using a bonding bushing to secure a fitting mechanically?;))
 
jaggedben said:
we just thread grounding bushings onto rainright connectors with no locknuts. Seems just as sufficient mechanically.
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I'd have to try it, but I think the grounding bushing would bottom out before it tightened against the box, at least on the 2". Probably violates the listing for the hub so guessing not compliant either.
 
Is there any reason I'm not allowed to use a box I have made at a sheet metal shop? Does it have to be listed? Can metal shops make listed boxes or get them listed? I'm asking for next time because the PVC box is already installed.
 
Coppersmith said:
That is an issue. With 2" and 1.5" Myers hubs there are two threads left for the bonding bushing. The 3/4" has no threads left. I was thinking of using pipe ground clamps on the pipes outside the box and bonding that way. Not compliant to 314.3 but the best I can do unless someone makes hubs with integral ground lugs.
Click to expand...
Meyers makes a bonding lockring, IE a lockring/nut with a bonding screw.
 
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