USA - Split 240vac to feed two GFCI circuits

Question

So I have a situation where I need to use a direct burial 10/2 with Ground to feed Two 120vac branch circuits by using the ground wire as a shared neutral.

Worse yet, the 10/2 cable has no neutral wire but does have a ground wire. This Direct burial 10/2 is installed in 3/4" PVC Sch 40 conduit. All of this is fed via a 30amp double pole breaker (L1 and L2).
Ground and neutral bus bars are connected together in this panel so effectively Ground and Neutral are one and the same leaving this panel.

So, can I take for example take one hot wire (Black wire (L1)) using the ground wire in the same cable having it act as a shared neutral, knowing it's a ground wire typically? I read the GFCI will work without Ground, yes no Ground.. keep reading...

So it would be a 120vac circuit Using L1 and Ground/Neutral. KNOWING I have no ground (a recipe for disaster), can I then run a ground rod and ground all the outlets back to the earth ground where this branch circuit will be located? All the outlets are plastic NEMA boxes with GFCI outlets installed 15amp.

The panel box is 150' from where the GFCI circuits are located so yes there is a potential for a small difference in potential from the ground rod to the panel box.

I understand there are two ways to wire multiple 20A 120V circuits. You can wire each one separately, in which case they use separate neutrals (e.g., 12/2 to each string of receptacles) or they can share the neutral. If they share the neutral, that is a Multiwire Branch Circuit or MWBC. An MWBC shares neutral, which saves the cost of one wire, and can do that because the current on the neutral from each leg cancels the other one out.

I think the Jury is in... the overwhelming majority so NO GO !!

I happen to have an Isolation Transformer by Victron Energy https://www.victronenergy.com/upload/documents/Datasheet-Isolation-Transformers-EN.pdf 2000watt, will this work? The theory would be to feed this with the 240vac 10/2 and just feed one 120vac circuit off of it. This appears to give me a true neutral and point for PE ground.

Answer 1

So I have a situation where I need to use a direct burial 10/2 with Ground to feed Two 120vac branch circuits by using the ground wire as a shared neutral.

It doesn't matter whether you "need to" do it. You CAN'T do it.

If this is an impossible-to-resolve problem for you, then you'll need to lurk on Craigslist until a UL-Listed 5 KVA 120/240--240/480V transformer pops up in the $100-ish range, buy it, and wire it into a service panel as a separately derived service to produce your dual 120V/20A circuits.

Or given the ampacity of the 10/2 I would hold out for a 7.5 KVA transformer. You'll need a so-called "subpanel" that is in fact a main panel. 30A main breaker on it (have to use a backfeed breaker), then XX solar breaker size and 20A for the branch circuit(s). As long as the panel bus rating is >60A you should be all set to run any size of solar up to 24A.

This Direct burial 10/2 is installed in 3/4" PVC Sch 40 conduit. All of this is fed via a 30amp double pole breaker (L1 and L2).

Then why are you thinking about ways to kill people? Just yank that 10/2 UF out of the conduit and pull in all the THWN-2 type wires you need for all your circuits. Blue-Blue-green(ground) for your solar 240V circuit, and black-white-red for your MWBC. Or just black-white and red-gray if you want two individual circuits. But I would do the MWBC myself.

Ground and neutral bus bars are connected together in this panel so effectively Ground and Neutral are one in the same leaving this panel.

No. They're only the same inside the panel. The moment they leave the panel, they are different.

Look. I get it. You see what is in front of your face. But what you don't understand is, when you bootleg neutral off ground, it isn't ground anymore. It's neutral. So now you have all the perils of an ungrounded system, which are the reason we added grounds in the 1950s. It gets worse: some half-wits think the neutral is still ground, so they attach it to things that are supposed to be grounded. Now a bunch of additional things become lethal.

No. Bad plan.

So it would be a 120vac circuit Using L1 and Ground/Neutral.

No. Calling it "Ground/Neutral" does not make it so. It's just neutral, and improperly insulated too.

can I then run a ground rod and ground all the outlets back to the earth ground where this branch circuit will be located?

No, that doesn't work. Dirt is a very poor conductor of electricity - that's why we bother to mine copper, instead of just wrapping dirt in THHN insulation and selling it for $300 a spool.

Ground rods are important, but in a branch circuit they mainly help with lightning and ESD (static electricity frying electronics). Ground rods do absolutely nothing to clear the kind of faults that are so dangerous when someone doesn't have grounds because they abused ground as neutral.

The ground rod does not help at all here.

Answer 2

NO.

You can't use ground wire for neutral. Neutral can carry current, that is why it is insulated.

About the only thing you can use is the 10/2 wire is for one circuit.

Will need to change to a single 15 or 20 amp breaker also.

You could pull the 10/2 and change it for a 10/3 or 12/3.

Answer 3

Absolutely not. You certainly may not set up new circuits in 2022 with bare as neutral and no ground. You must have separate neutral (must be insulated) and ground for 120V branch circuits.

There are some vaguely related situations (stoves and dryers could have bare neutral pre-1966; similarly old circuits didn’t need ground) but that’s only for circuits that were legal when installed at the time. You can’t set up new work like that.