Wood/metal stud (hybrid) construction and NM-B

[PetrosA]

I came across something today for the first time outside my usual work region. Residential construction using a hybrid of wood and metal framing on the interior walls with what appears to be an intent of using bays framed with metal for delivery of air (IOW, there are no ducts installed). Not all of the bays framed with metal studs were for air handling. Romex was used throughout and many of the boxes in the interior walls had their clamp holes sealed with foam insulation as were any grommets I saw in the attic.

They used the typical plastic grommets where the NM-B passed through steel and luckily I carry 3/4" snap-in grommets on my truck and was able to use them from the attic down into a wall.

My question is about penetrating up from the basement though... It seems like they laid a metal channel down on the wood subfloor and ran both their metal and wood studs from there. If I need to penetrate that channel from below, what's the best way to protect romex from the edges of the channel after I've drilled up through it? It's too thick to use any kind of snap-in grommet that I've seen. Anyone with experience in this kind of building method have any ideas to share?

Thanks

 

[shepelec]

How about a stub of pvc? It could be held in place by the firestopping.

 

[ActionDave]

From the bottom up I drill a 1 1/4 or 1 3/4 hole through the wood only, stopping my hole just before it completely penetrates and pop the wood disc out, then switch to a 7/8 or 1 1/8 hole saw to cut the metal and snap in a 1/2 or 3/4 plastic grommet.

If you can go from the top down I do it the opposite and drill a big hole in the metal first and then small in the wood sub-floor.

 

[iwire]

I use a hole saw larger than 1" to drill out the metal, once the metal is out of the way I use a wood bit 1" or smaller to drill the wood, the wood holds the NM(s) away from the metal.

 

[PetrosA]

So I guess this a pretty common building style in other areas... Any ideas of how to deaden the sound of a Diva dimmer switch as it clunks on and off in a metal bay?

 

[shepelec]

Spray foam or insulation will help stop the sound travel.