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I built a shelter around my pump down here in central Fl. For a pump business I was suprised they ran 12-2 romex in the conduit from the breaker box on the power pole. The pump has red, black and green going into the well. They both ground on the pressure switch case. I bugged a receptacle on the black and ground and ran my miter saw and compressor to build the shelter with no issues. I would like to have a light in there and a gfi for power to work in there if needed. Is there any safe way to use a gfi or a light in there short of removing the romex and pulling re-pulling individual thnn wires with a neutral. I'm not sure the outdoor panel for the m/h bonds the neutral and ground, I have to recheck. Thanks. GBY

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    I'll let the experts give the full (very detailed - ground rods, etc.) answer. But the short answer is: Replace the 12/2 with hot/hot/neutral/ground wires and put in a small subpanel. Run the pump 240V and put in a couple of 120V circuits all in the subpanel. Ground should be separate from neutral in the subpanel. Commented Dec 10, 2019 at 4:05
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    What size is the conduit in question, and is it a continuous conduit run from one end to the other, or just a protective sleeve where the cable enters the ground? Commented Dec 10, 2019 at 12:43

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Stop using ground as neutral. If your grounding system is anything shy of perfect, you'll energize everything that's supposed to be grounded.

The fact that it has conduit on the ends doesn't mean it's entirely conduit. If the line were direct burial, the descent to depth is required to be in conduit for physical protection. *Push and pull the wire. If it has about an inch of relatively free play, then it's in conduit.

Use a subpanel

If it is indeed conduit, then you can fish in THHN wires: two hots, a neutral and a ground, all #10. Bring that to a subpanel, and have a 20A double breaker in the sub power the well, and 20A single breakers feed convenience outlets and other 120V loads. You will also need a local grounding rod, or rather 2 rods 10' apart unless your AHJ will let you use the well pipe. AHJ=authority that issues permits and inspects.

You can then upsize the breaker in the main panel to match the wire (30A for #10, 50A for #8 THHN).

Otherwise... Use a transformer

For casual loads like you might plug into an outdoor receptacle, a 1.5 KVA transformer will suffice. If you want a LOT of power out there, a 5 KVA 1-phase transformer off Craigslist will do. Do not use a "step-up/down transformer" because that can accidentally put 240V on your hot and 120V on your neutral. You need an isolating transformer. For small loads like this, I would leave it isolated, i.e. don't bond neutral to ground. And have it feed a GFCI recep for statutory reasons.

Why not bond? Bonding (vs isolated system) is a double-edged sword. An isolated system has no relationship with ground, so touching hot is harmless - power doesn't flow because there's no loop. On the other hand, bonding neutral to ground forces hot to be within 120V of ground, which protects you from leakage from the 7200V transformer primary. But in this case, the transformer primary is + and - 120V from ground (summing to 240V), so bonding does not make it any safer. Therefore isolation affords better safety.

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  • With subpanel option: Shouldn't OP replace original 20A breaker in main panel with 30A to get the most out of the #10 wires? With either option: I get totally confused about grounds - are they needed here since it is a separate structure? Commented Dec 10, 2019 at 20:49
  • @manassehkatz Dur, your intuition was right on both. Commented Dec 10, 2019 at 21:00
  • Not my intuition - my reading your other answers over the last couple of years. Commented Dec 10, 2019 at 21:01
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    @manassehkatz Not a fan of that. That would put the well on GFCI. Like a refrigerator, a well pump attached to a 300' metal pipe isn't helped much by GFCI, and is hurt by the risk of nuisance trips. Noting your add, yes, Murphy's Law says that the trek outside to reset the well pump GFCI will happen when you're in pajamas and it is somehow both -10F and raining. Commented Dec 10, 2019 at 21:08
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There might be a safe, code compliant way do this with the existing cable in the conduit - if that cable is UF type. (If it's NM, it's probably already a code violation. However since the conductors inside the cable are probably THWN rated, and possibly stamped THWN, it might be passable.)

But none of the options I can see would be simpler, easier, cheaper, or safer than just running replacing that cable and adding wire for a second GFCI protected circuit for a light and a convenience receptacle.

The motor circuit has totally different rules than a general purpose circuit you'd use for receptacles / lights. In some cases you can put a motor on a general purpose circuit, but not likely in this case, especially since you'll want GFCI protection on the general purpose circuit and you won't likely want it on the motor.

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  • Actually, you may want might even be required gfci on the pump. But I don't know the code so just a comment. Commented Dec 10, 2019 at 14:45
  • Where are you finding NM with THWN rated wires inside? I've never even heard of such a beast. I'd argue that it's very likely that the internal wires are not TWHN rated in any random piece of NM cable.
    – Nate S.
    Commented Dec 10, 2019 at 20:35
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    Nate S, Yes, they are. If you remove the jacket and look at the individual conductors, they often don't have markings because they are not required to. But starting in the 2008 NEC, equipment that says that you must use 90C rated wire resulted in the release of "NM-B" cable. Suppliers don't want to have to carry inventory of two kinds of NM cable, so everything you buy now is NM-B, meaning the internal conductors are rated for 90C, even though you still size it for 60C. UL just calls for 90C PVC insulation which translated to the mfrs using THHN/THWN inside since they already make that.
    – JRaef
    Commented Dec 10, 2019 at 21:24
  • Wow, impressed with all the comments and the knowledge here. I have to do a little digging or disconnecting to find more info. They did run 12-2 romex in 1/2" cantex conduit. I imagine that it's continous to the pump. I can't imagine they would bury romex as is but if the put it in conduit, Really was hoping to figure it out without repulling. Might have to let this set as other projects have more priority
    – K S
    Commented Dec 11, 2019 at 0:28
  • OK, latest update. I opened the mobile homes 200 amp breaker box at the pole. It has a double breaker for both hot legs, 90 amp double breaker for the heatpump package unit. It also has the 20 amp pump double breaker. I added a 20 amp double breaker with 12-3 with a ground uf cable in conduit out to two sheds.
    – K S
    Commented Dec 12, 2019 at 0:23

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