Subpanel fed from single conductor

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mvwsr

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NEFL
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FiberSplicer
So im trying to help my GrandMother & Mom with a subpanel(b) issue in a detached garage. They mentioned the golf cart stopped charging after sometime recently but cant pinpoint exactly when. Everything is 110 in this garage. And all the lights work.
Im thinking it is a result of recently construction/electrical work, somehow damaged or dropping the neutral.

So what i know is the house had its subpanel(a) moved. Flipping from previously, inside the half bath, to the otherside of the wall making it in the garage. (attached garage)
The location of the 2pole breaker previously tagged "shop" has been made to the new air handler in the garage. trying find the new source for the detached shop I found a single #2 spliced outside the panel to a #10 going into an open KO. This is a single pole 20. The subpanel(b) at the detached garage has #2 mhf in conduit ,LB , with 1 leg isolated(not connected) and #6 EGC from a ground rod just outside.
I can see the detached subpanel(b) is floating neutral with the neutrals & grounds bonded in the same buss. Im measuring full current on ground conductor 1.7A with lights, trying to spin up the grinder, i found the clamp at the ground rod arc'n&spark'n. I couldn't get to it with the flathead to tighten, so I changed it out. No fix.

The charger works from another outlet at the attached garage. I also found when trying to use a bench grinder, the lights started brownout. So as it is ,low current LED's and other 110 devices work, but the high current loads expose the problem this subpanel circuit cant handle the load.

To summarize, main has 100a 2pole going to the attached garage subpanel(a), feeding detached garage subpanel(b) with a single conductor. Both subpanels the neutrals, grounds are improper bonded. The last subpanel in the detached garage has just single leg, no neutral that i can find feeding it. How tf? I mean i think I know how its working (kinda) but how to? Lol
 
Forgot to mention, I put a locator on the open conductor and neutral conductor from subpanel(b) it crosses paths with a new gas line for a new hot water heater. I didnt dig in those locations, but I did find a single #2 coming from the dirt into the attached garage coming from the source subpanel(a). Digging at that I found a splice, atleast a tape job coming out of a 1" iron pipe. It was raining abit and its being my last day here i didnt want to get any deeper into exploration. I cant say if the tape is as fresh as the recent rehab project , but the iron pipe is well rusted and too small to have had all 3 of the mhf that I find in the LB at the detached garage. Its possible when the did the gas, they did some fix before anyone home realized it, I guess ill have to spot hole it a few times along the new trench to see if I see the 2" pvc with the mhf .unfortunately thats gotta wait until I comeback in April or July.
 
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