Electrical Puzzle

So my client and his father-in-law are both electricians, and we were all wondering what was going on with a generator panel.

They had an old panel and breakers. The branch wiring they used to the generator panel and all the breakers were multi-strand AL -12/2, but all the branch wiring was copper, single strand 12/2. All the wire caps were AL CU mix without the proper caps.

Every time the heating unit turned on (which had a 20 amp breaker with the multi-strand AL) it would make a loud humming noise.

There was more to it, but that’s the gist. Any help explaining if its good, bad, or what the heck is going on is appreciated. My clients were scratching their heads a bit. Thanks!

Humming ?
It doesn’t know the words…
Just Jokin’

It may be something like this

Can you post a picture? I doubt the wiring from the transfer panel was aluminum, especially since it is not likely to be from the 70’s.

Ian, I’m just wondering, since I used to install back up generators and Transfer Switches.

The “ON DEMAND” Transfer switches that come pre-wired have never used AL to my knowledge.

If it’s an automatic transfer switch, then it likely did not come pre-wired, and they could have put anything in there. Since you mentioned branch wiring from the transfer panel, then it must not be automatic. Until lately, the Automatic Transfer Switch transferred all the power to the generator-not just a few circuits, so it took a sizable genset to match the building load, which why most home standby units only drive a select amount of circuits.

I appreciate the feedback. I will try to post pictures later, I am on another inspection at the moment.

It was not an automatic switch panel, it looked like it was from the 80’s if that helps. Even the older ones I find that have AL don’t use multi-strand though…

Is this when powered by generator, utility grid or both.

I think you are looking at tinned copper. The conductor material should be written on the insulation.


We checked, it was aluminum