I am in the process of renovating a house that was built in 1933, and had an addition put on in the 1960's. Original 1933 panel is 100 amps. When the addition was put on, the electrical drop was moved to a 200 amp panel in the addition, and the old 1933 panel was turned into a subpanel.
The old panel is receiving two hots and a neutral from the main panel, and the neutral is just a bundle of wires with no inner sheathing.
In this subpanel, the grounds for the circuits that have them (the old 1933 circuits did not, but some had apparently been added) were just attached to the neutral bus bar, mostly double-tapped with their own neutral. A ground wire was added to the neutral bus bar, and it is attached to the copper pipes in the crawlspace at a point where they go into the earth under the house. There is no ground wire going back to the main panel.
I know that there are several things wrong here. There should not be double taps, and in a subpanel the neutrals and grounds should not be bonded on the same bus bar. And there should be a ground wire going back to the main panel. There should be a second bus bar in the panel for the grounds, but there isn't because the panel was originally a main panel.
Unfortunately, a heat pump was added at some point right next to the new panel, which means that there are large ducts blocking access in the crawlspace to the place where I'd thread wires to reach the new (main) panel. I might be able to push a wire down and hope that they poke out where I can grab them, but I haven't tried, so I don't know for sure that that would work.
My understanding at this point is that the best solution is to try to run a new ground wire from the neutral/ground bus bar of the new (main) panel and connect it somehow to the grounds (and the panel) of the old (sub) panel. Could I just twist them together tightly, since there isn't a bus bar for them? Do I have other options if I can't run the wire due to the blockage in the crawlspace?
Do I leave the ground that is connected to the earth rather than the main panel in place or take it out?
And what do I do with the unsheathed neutral in the subpanel? Right now it is touching some of the ground wires in the box, and that can't be good. Can I just wrap it up in electrical tape?
Thanks in advance.