I recently found that the neutral bar and ground bar in my home's subpanel have no resistance (0 ohm) between them (when the neutral feed to the subpanel is disconnected). I root caused the symptom to one particular pair of neutral and ground wire. That leads to the junction box pictured below.
In the picture, you can see 3 wire nuts. The red ones each have 2 wires in it. The grey one has 3 wires in it: a thick wire (which I presume to be neutral), a bare aluminum ground, and a green wire. (EDIT: added this paragraph in case the picture is not clear)
I believe that the right thing to do here is to remove the neutral cable from the gray wire nut, and cap it off. I found the installation manual of the appliance, and the manual seems to support my belief.
But I'm a bit hesitant because the existing setup of the wire just seems too crazy. I wonder if I'm missing something. Is there any possibly valid reason that this junction box was wired this way?
My home is in California.
Best Answer
It was wired this way because Goober the appliance installer guy, whose job is pushing heavy appliances around on dollies, needed to hook this up and collect the customer's cheque ASAP. Goober had a 3-wire appliance to attach, and saw 3 wires in the wall, and boom zoom and out the door.
You actually have 4-wire service to this range. However it is in aluminum wire, which is a serious problem. If the ground is aluminum, surely so are the hots and neutral. None of those splice connectors are rated for aluminum wire.
You will need to obtain some "MAC Block" connectors, which are a somewhat miniaturized version of Polaris lug connectors, which are proven to work well with aluminum.
... By the way, fix that schizoid lid.
On one hand, you've got a 4x4 junction box with a 2-gang mud ring that has 6-32 mounting screws in the correct positions to mount 120V outlets and switches. On the other hand, you've got a common 4x4 junction box lid that expects to attach to the corners of the box.
I see now that the junction box is blocked in by cabinetry. That isn't allowed and is a serious code violation: not only is it uncovered, but flammable materials are inside the box! Get a vibrating tool and cut away enough of the cabinetry above it that it's possible to mount a normal junction box cover plate the normal way. It looks like what's above that is nothing special, just the back of a drawer box or something, so it won't do any harm to remove the offending material.
Now you need a different lid that attaches to the 2-gang screw locations... a real electrical supply can help you out there. Home Depot won't have it, it's not popular...