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Freelance–
What you got with your 240V, three-wire circuit is actually a 240/120V circuit. It has 4 conductors, right? black, red, white, and bare (or green).
Check it with a meter…
Between the black and white = 120V
Between the red and white = 120V
Between the red & black = 240V
This is the same setup that’s used for electric clothes dryers. It provides 240V for the heating elements, and 120V for the timer/controller and the light bulb in the drum.
The two hot conductors of this type of circuit (called a multiwire) are protected by a 2-pole circuit breaker. This is functionally the same as two single pole breakers, with the handles tied together. The handles are tied together for safety–if either pole overloads or faults to ground, both poles open, and if you intentionally open one pole but are clueless about the multiwire arrangement, you open the other as well.
So, my advice is to check the size of the neutral conductor. If it’s ampacity matches the circuit breaker rating (14 gage for 15A, 12 ga for 20A, 10 ga for 30A), then the breaker will protect the neutral if there’s a short or overload from one phase conductor to the neutral.
If the neutral is sized correctly, go ahead and install a j-box ahead of the pump motor terminals and choose a pole (red or black) from which to pull 120V. Run from there to a 2-gang box, one GFI for the heat tape, one single receptacle outlet for the timer/controller.
The best way to choose the pole is to look over the main panel and see if the poles are roughly evenly loaded (based on the actual max. load)–this will require you to inventory the number of lights, appliances, etc on each circuit. That’s a good thing to know anyway. If the poles are not evenly loaded, pull power from the pole that’s less loaded.
One more thing–if there is no exposure of the heat tape to people and animals, you may want to get
a ground fault interruptor rated at more than the 6mA at which personnel protections GFIs are rated. A higher leakage current will reduce nuisance trips and frozen pipes. Such a GFI can be had from Graybar or other major electrical supply house.
Best of luck.
Replies
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The main reason you can't tap into the well wire is that the breaker for the well is probably 30 amp. You would have to reduce your branch off down to 15 or 20 amp.
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Thanks to all who responded. Especially to CAP whose assessment and advice is most concise and useful. One additional question regarding this same system: since this is a dedicated irrigation well, it will only run when the timer/controller calls for water. In your experience, is there a suggested type or model of relay I should use? The controller is a Nelson 8520.
A clarification regarding use of a GFI rated at higher than 6mA: the controller will be mounted outside, under the eave of the well enclosure. The enclosure is to be weathertite and lockable. Does this meet the criteria for a non-personnel protection GFI?
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The neutral and ground (or more correctly, the grounded and grounding conductors) are tied together at the service entrance only. At all
other places, including any subpanels, they are separate. That is why panels have the option of isolating the neutral bus from the
enclosure and offer ground bars as an add-on.
Think of the grounding (bare or green) conductor as the safety valve. Should any fault occur, it provides a low resistance path to ground
thru the panel instead of thru your body.
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Got a 3 wire 240v circuit powering a well pump. The well is a dedicated irrigation source. Need to pull 120v off the 3-wire to power the valve controller's transformer, plus a GFI recep. that will run a heat tape in winter. Have checked and black and red are connected to opposite sides of source. Question: is the white wire adequate ground for the 120v side or do I need to establish an independent ground? The well casing is 6" black pipe and would be very easy to use.
*I think we will have to wait for the experts to clock in on this one but if I have correctly absorbed electrical info from the maintenance guy at work for doing my wiring then I think you have a bad idea there.You may have to run another circuit.
*Also not an electrician but I'm sure you'll need a breaker for your 120V circuit. You can't just tie into the 220 line and expect the two pole breaker to save you're single pole circuit.Take your 220 line into the pump house (or wherever it's going)and use it as the supply to a new breaker box. This box can have 220 and 110 circuits all with their own breakers.I think you'll also need a ground from your main breaker box to your new subpanel.
*Also not an electrician. Most 220v single phase circuits use two hots and a ground. For 110/120v circuit you will need to run a neutral, which would give you four wires - two hots, a neutral, and a ground. As Ryan suggests, a sub panel is probably a good idea (and most likely a code requirement.) There are some considerations in adding a separate sub-panel if it is in an out buildng, however. It is my understanding that you would usually want to run (or be required to run) the separate neutral and ground wires (technically labeled as "grounded" and "grounding" so as to thoroughly confuse the uninitiated when venturing into National Electrical Code territory...) back to the main panel where they are tied together. I believe that usually you are required to also have a ground rod at the out building in addition to one that is tied to the main panel if the out building is over a certain distance from the main building.
*I'd like an electrician to jump in here. I thought that now, the grounded and grounding wires were not tied together at the main panel anymore. There used to be only one neutral bus bar where all ground and neutral wires were connected. Now panels have a ground bus bar and a separate neutral bus bar that is insulated from the panel. I don't know why there was a change.I may be wrong but I was under the impression that the neutral and ground wires were now kept separate everywhere within the house.
*To have electricity I had to install it myself. I bought the pole and all the hardware. I had to dig the hole for the pole, and wait for the inspector to come out and inspect the pole and the hole. Then I was allowed to put the pole in the hole and get on with it.I bought a Siemens box. It is 200 amp service, with meter mount. Technicaly an rv service box. It has one buss bar for both the nuetral and ground. You can buy a seperate buss bar so you can have them on seperate bars, but it is not required. This is not a box that has been sitting around for a while in the back of the store. It is brand new, and was the best the store had. The next time the inspector came out, I pointed to the common bussbar with both ground and nuetral coming from it, and asked why even have a seperate nuetral wire, since they both go to the same place ??? He said some mumbo-jumbo about a nuetral not being a 'true' ground, and I decided not to push it because he might fail me. I wanted my electricity. LOLI still don't understand why it can be said that if two wires go to a bussbar that is grounded directly to a ten foot 5/8 rebar driven all but 6" into the ground, one is grounded and one is not ????To answer freelance's question, (and you didn't hear it here, freelance, if you say so, I'll deny it. LOL)... In most 220 curcuits, the two poles, (red and black), are essentialy connected to seperate 110 curcuit breakers. (ie, most 220 circuit breakers, where you have one breaker with two connectors, they are essentialy two 110's bolted together side by side.) If you absolutely have to do it this way, I would suggest you connect the black to black, white to white, and ground the green to a good ground source. It should work that way. This post will most certainly bring great amounts of flame from others here. Now I'll go and put on my asbestos jumpsuit.
*Freelance--What you got with your 240V, three-wire circuit is actually a 240/120V circuit. It has 4 conductors, right? black, red, white, and bare (or green).Check it with a meter...Between the black and white = 120VBetween the red and white = 120VBetween the red & black = 240VThis is the same setup that's used for electric clothes dryers. It provides 240V for the heating elements, and 120V for the timer/controller and the light bulb in the drum. The two hot conductors of this type of circuit (called a multiwire) are protected by a 2-pole circuit breaker. This is functionally the same as two single pole breakers, with the handles tied together. The handles are tied together for safety--if either pole overloads or faults to ground, both poles open, and if you intentionally open one pole but are clueless about the multiwire arrangement, you open the other as well.So, my advice is to check the size of the neutral conductor. If it's ampacity matches the circuit breaker rating (14 gage for 15A, 12 ga for 20A, 10 ga for 30A), then the breaker will protect the neutral if there's a short or overload from one phase conductor to the neutral. If the neutral is sized correctly, go ahead and install a j-box ahead of the pump motor terminals and choose a pole (red or black) from which to pull 120V. Run from there to a 2-gang box, one GFI for the heat tape, one single receptacle outlet for the timer/controller. The best way to choose the pole is to look over the main panel and see if the poles are roughly evenly loaded (based on the actual max. load)--this will require you to inventory the number of lights, appliances, etc on each circuit. That's a good thing to know anyway. If the poles are not evenly loaded, pull power from the pole that's less loaded.One more thing--if there is no exposure of the heat tape to people and animals, you may want to get a ground fault interruptor rated at more than the 6mA at which personnel protections GFIs are rated. A higher leakage current will reduce nuisance trips and frozen pipes. Such a GFI can be had from Graybar or other major electrical supply house.Best of luck.
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......I still don't understand why it can be said that if two wires go to a bussbar that is grounded directly to a ten foot 5/8 rebar driven all but 6" into the ground, one is grounded and one is not ???? .....
They ARE both grounded. In NEC terminology, one is referred to as a grounded conductor, the other is referred to as an equipment grounding conductor.
Lee