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View Full Version : Fire Hazard? Expanding Foam - Electric Boxes



molo
05-08-2009, 06:47 PM
Is there a fire hazard created when you put expanding foam around electric boxes? What, if anything, is safe when using the foam around a box?

Thanks for any replies:)

Speedy Petey
05-09-2009, 04:46 AM
Supposedly foam is fine around boxes. Just make sure all holes are sealed so the foam does not enter the boxes.

Thatguy
05-09-2009, 03:01 PM
Supposedly foam is fine around boxes. Just make sure all holes are sealed so the foam does not enter the boxes.
In that case heat dissipation from the box due to IČR loss and bad wirenutting/connections depends on heat conduction through the copper and the cover plate being at room temp. I guess the NEC has already figured the boxes would be insulated with no air flow around them.

Speedy Petey
05-09-2009, 03:21 PM
I have never heard of "heat dissipation" around electrical enclosures being an issue.
A failed connection just need to be contained for safety.

I would say the NEC definitely has considered this assuming many boxes and enclosures are on exterior walls and ceilings.

Thatguy
05-09-2009, 03:28 PM
I have never heard of "heat dissipation" around electrical enclosures being an issue.
A failed connection just need to be contained for safety.

I would say the NEC definitely has considered this assuming many boxes and enclosures are on exterior walls and ceilings.
I guess that means that enclosures have, or the air in them has, never gotten to 120 °C :D
"Wood slowly chars [at] 120°-150°"
but failed connections certainly have
"Electrical arcing [up to] to 3750°[C]

I guess air is pretty good thermal insulator.