You should mount the box on the joists or wall, and you need to use shielded
cable.

"dean" wrote in message
ups.com...
Hi all,

I need an electrical wizard to advise me here. I am installing a new
hot air wood furnace next to an existing electrical furnace. I have run
the 20 amp cable along the basement ceiling ok and now I need to drop
down to the furnace. I want to add a cut-off switch so that I can
isolate the thing in an emergency.

Can I put this switch on the plenum? In a metal box? The other furnace
has a small breaker box on its plenum with 3 breakers inside, so I
can't se why I should not be able to do this. I have used standard
orange 10-gauge romex cable.

Plenum temp is set typically to turn on fan at 170, and will open an
emergency heat dump at 200 in case of a problem.

Thanks!

Dean