Air gaps in electrical boxes

I'm in the process of stuffing rockwool into the space between my studs. The electrical boxes I'm using have several small holes in the backside of the box. One of them is for the ground screw, but there are about three or four others. The diameter is maybe 1/8"-1/4". Should I caulk/seal these holes? And a related question: Seems like electrical junction boxes are generally weak spots in an isolating wall. Should they be stuffed with rockwool? Is that to code/legal? My suspicion is no, but I just want to check. Thanks!

I had a couple boxes attached to framing, and I used sealant to cover up the holes. If you can, if you have access to the back side after the drywall is up, seal around the box too. Otherwise, the best way is to surface mount the boxes and not make any penetrations or holes for boxes. You can also surface mount the conduit or just have the conduit poke through the wall and surface mount the box.

If you can get at them, cover the back/outsides with putty packs. Or use plastic boxes instead of metal. Do not fill them with rockwool -- the parts get warm in there and are designed to air cool. There's electrical code restrictions on how much room is in there (# wires, etc).

gdgross wrote:

I'm in the process of stuffing rockwool into the space between my studs. The electrical boxes I'm using have several small holes in the backside of the box. One of them is for the ground screw, but there are about three or four others. The diameter is maybe 1/8"-1/4". Should I caulk/seal these holes?

You should not caulk them - the UL listing for the box does not indicate that this is acceptable - and thus - should there be a fire - you could find yourself liable (even to the point of your insurance company abandoning you) for violating the UL listing and the electrical code.

And a related question: Seems like electrical junction boxes are generally weak spots in an isolating wall. Should they be stuffed with rockwool? Is that to code/legal? My suspicion is no, but I just want to check.

As Z so correctly advised you - do not stuff them with rockwoll (or anything else) - for the same reasons as noted above. He also advised you correctly on what to do......... use putty packs to seal the box to the wallboard. These have excellent STC ratings. Rod Thanks![/quote]

Okay, I'm showing my ignorance: what are putty packs?

There is some info here about them... http://johnlsayers.com/phpBB2/viewtopic ... c&start=21

Thanks, I just called the contractor supply store where I got my RC and they carry them. I will pick some up tomorrow!

See this post in the Building Products forum for an online source for this product. (Note that they are actually called "Putty Pads.")