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Question about wiring for 240V well pump

Posted by empjr (My Page) on
Sat, Jan 20, 07 at 15:25

My 1HP 240V deep well pump runs on a 12-2 w/gd NM cable which goes from the box in the basement out through a hole in the concrete wall and then underground to the well house. There is a joist-mounted junction box on that cable in the basement which I opened earlier today to see what it was there for. Apparently it was put in just to splice two pieces of cable together because there is white cable going in from the breaker box and yellow cable going on out to the pump. What I don't understand is that the black and white insulated wires in the cable are connected with wire nuts as they should be, but both ends of the bare ground wire are also connected together with wire nuts and wrapped with black tape from the cable sheathing to and over the wire nut so that no part of it is exposed. And of course the bare wire isn't screwed to the metal box like I would expect it to be if it was serving as a ground wire. All that leads me to think it must be carrying current or acting as a common on that 240V circuit because if it was serving as a normal ground wire it wouldn't need to be insulated and wire nutted together. It must work OK since the pump works fine, and I assume that it was wired by a licensed electrician when the house was built 10 years ago. But I would still like to know just how that hook-up works and if it's legal. I always thought that 240V cables used 2 hot wires with one common wire and a ground wire, but this hook-up doesn't seem to use the bare wire for a grounding wire. I have learned quite a bit by reading this forum, but as you can see there's a lot about the wiring for 240V appliances that I still don't understand.


Follow-Up Postings:

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RE: Question about wiring for 240V well pump

I would assume it was installed by a knucklehead.

Check at the breaker box that the bare is indeed grounded and/or verify with multimeter that the bare at the j-box has continuity with a nearby ground.

Then ground that j-box.


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RE: Question about wiring for 240V well pump

240v circuits have NO neutral, or as some incorrectly call it: "return", wire. A straight 240v circuit is just two hots and a ground.
YES, a "2-wire" cable can be used for this. Recent code requires the white to be re-marked with a permanent marker, paint, or equivalent, but it is not at all uncommon to see a plain old 12/2 feeing a well on a 240v circuit.
This is perfectly common, legal and safe.

Thing is, folks casually toss around terms like "240v" or "220v". This is fine if that is what you are really talking about.
Motors, many power tools (also motors), air conditioners (also motors), welders, etc, are mostly straight 240v. These circuits are two hots and ground.

Dryers and household cooking appliances are typically 120/240v. This means there are 120v and 240v loads in the same appliance. These circuits are two hots, neutral and ground.


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I forgot...

I did forget to mention after seeing the post made while I was typing.
Yes, the box must be grounded.


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RE: Question about wiring for 240V well pump

OK, then it looks like I need to ground the bare wire to the jct box after checking to see if it is connected to the ground lug at the breaker box. I assume it's safe to touch the bare grounding wire even though somebody went to the trouble of insulating it with electrical tape, but I think I will trip the breaker anyway before opening that jct box again.

Thanks to both responders for the quick answers. If I hadn't asked for your help on this forum and the jct box was left ungrounded like it has been for years, some future owner or worker could possibly get a fatal 240V shock later on if one of the hot wires ever came loose for some reason.


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RE: Question about wiring for 240V well pump

Wait a minute.

Are there any 120 volt systems in the well house such as a light? Whomever installed this may have used the ground wire as a neutral so they would have 120 volts available for something like lights.

If this is the case, that wire is a current carrying conductor. It sounds as if they were trying to do it half assed right by not grounding the neutral.

Do not open that circuit with any power on. It will provide the same shock as a hot wire if they did use it as a neutral.

Also, if the wire used is actually NM, this is also wrong. NM is not allowed to be buried. UF would be correct.


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RE: Question about wiring for 240V well pump

Somebody s wrong but its NOT Petey_Racer. Powerco supplies 210~240v single phase to residencial customers. Not 2x 110v which implies each "leg" is indentical. 220v motors require 220v and the amperage on each of the two wires may be say 5 amps for 1/2hp but its the same 5 amps on both legs. Not 2x5.
A 1/2 hp 110~125v motor with 110v on one leg and neutral on the other will draw about 9.8amps. Same hp more current. Hook a clampon amp meter over both legs of the motor and you get 0 amps not 10 amps so 2x15x110 may offer the same result as 15x220 doing the math, but your logic is ? Apples and oranges. 115v@15a=~1hpmotor. 230V@15a=~3hp motor. The supply is 220v be it 1, 2, 3, or what ever number of wires ya like. Just word play.


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