Hi there everyone,

I've got a bit of a complicated question for you:

In our house, we are replacing our old panel with a new one. The old panel has NO MAIN BREAKER!

The new panel is in place, but in a different location and there is lots of other cable to be pulled, etc before it's ready for hookup.

My question is this: From the old panel, there is a 40amp breaker that used to tie into a shop, but now is doing nothing. I was wondering about being able to temporarily tie into the new panel using this breaker ( tying into the panel's 100amp main breaker, that is ).

The main issue right now is that the cable leaving the old panel's 40amp breaker is, I think, BX - it has a red, white, and black wire, but no grounding wire at all. It leads to a metal junction box.

I was hoping to take a piece of #3 NM from that junction box, temporarily to the new panel to energize 1 or 2 15amp circuits so that I have some power to work with while the old panel gets taken out ( in several weeks ).

So the issue is that the NM has a grounding wire, obviously, but the BX does not. I was wondering if you can use the ground from the new NM cable tied into the junction box, and will the armor on the BX ground it?

Of course, for now, this isn't a code thing, but I just want to know if that's a safe thing to do for a few weeks until the proper wire can go in - obviously, I don't want to try to attach the new NM cable right to the breaker since there is no main breaker to shut off.

Thanks for any info!