Grounding for sub panel breaker

Home Improvement Asked on May 8, 2021

We have an old cabin with 4 fuses in the main 60 amp panel, and a sub panel with a handful of breakers. The sub panel is fed by 3 wires instead of the modern 4. The 4 fuses are all wired with 2 wire aluminum wiring.

I know that code allows you to add one grounding wire to serve multiple circuits. I had one open spot in my main panel, so I added a 10 gauge solid grounding wire. My question is if code allows me to ground receptacles on a breaker in the sub panel with the grounding wire from the main panel. I just did this (Grounded some outlets run off of the main panel fuses and some off of a sub panel breaker) with my one grounding wire and my circuit checker said the open ground was gone and showed proper wiring, but then I read that a single ground wire can only be used for multiple circuits that terminate at the same panel.

I can read that to say that my sub panel that the breaker is on terminates back at the main panel as do the fuses, or that the breaker terminates at the sub panel, and the fuses at the main panel so it is not ok. (At least I am not bonding neutral and ground at the sub panel)

I would appreciate any help I can get on this.


So it sounds like what I did does not meet code. Is this kind of grounding dangerous? Ineffective? Just less effective than proper grounding? Basically I am wondering if I should take it out. Also, given the 2nd photo below, I am not sure if I could run the grounding wire to the subpanel as suggested, or if I would need to add a grounding bar to do so. We will eventually need to bring someone in to straighten all this out, but I am trying to make things better, not worse, until then.

As requested, I have added pictures below.
Main panel

The first is the main box. There was one grounding screw available in the middle on the top that you cannot see here behind the wires. It is where the green wire on the top connects.

Here is the subpanel. I don’t think the ground and neutrals that are here are separated. Given there is no grounding wire coming in from the main panel, I do not see how these can be separated bars (upper left), but I am no expert.


One Answer

The ground retrofit rules say you need to take the ground back to the same panel the circuit comes out of. So maybe this ground you just installed actually goes to the subpanel, and the subpanel has its own ground wire back to the main.

Also, I would flip that around, and make it so the fuse box is a subpanel of the breaker panel, and have it be powered off an AFCI breaker. That will be a good hedge against most aluminum-wire troubles.

Answered by Harper - Reinstate Monica on May 8, 2021

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