I'm currently rewiring my new-to-me detached garage. Garage is from the 70's but has a newer Siemens panel (previous owners added a hot tub). The feed from my service panel is a sheathed 4 conductor cable in buried conduit, but both ground and neutral are bonded on the neutral bar. Hmm, ok well I lucked out and have the 4c feed, so I can just add ground bars and get the neutral and ground separated per code, right?
Here's where I'm a bit confused. I went to the service panel to just lay eyes on the same four conductors, but I only have the two hots and neutral there. The green ground wire is nowhere to be seen. Looks very much like the same cable, was looking to see if ground was snipped at the clamp but can't see any evidence of it.
I found this thread: Is my ground correct at my subpanel?
... which describes some techniques for checking out the ground on a subpanel. As described there, I disconnected the feed neutral and ground conductors in my garage and put my meter across them- no resistance. So the ground conductor in my garage has continuity back the neutral in the service panel, but I don't know how!
And now, my question: Beyond what I've done so far, how much should I do to verify this ground before separating neutrals and grounds in my subpanel? I'd think I'd like to know it's something substantial and not accidental. Is it possible it's tied to the conduit somewhere, and the conduit to the chassis of my main panel? I suppose I could tear out some drywall above the main panel to see what I can see.
Odds and ends:
-There's one access on the conduit where it enters the house- nothing interesting in there, just same sheathed cable.
-The subpanel and garage does have two GEC spiked into the earth behind the garage away from the house.
-Conduit leaving the garage is PVC, metal entering the house.
Thanks for any advice.