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OT: 3-wire service, 4-wire device

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  • OT: 3-wire service, 4-wire device

    Just bought a used but like-new Kenmore electric range/oven to use as a powder coat oven. The oven has a 4-wire connection. My 220VAC outlets are 3-wire, and running a neutral wire back to the breaker box isn't an option. The only 110VAC loads (lighting and control circuitry) are small. Theoretically, I suppose the correct solution would be to put a small 2:1 transformer across the 220V supply and connect one leg of the 110V secondary to the oven's neutral connection and the other leg to one leg of the 220V supply. However, given that the 110V loads are small, I'm inclined to connect the oven's neutral and ground wires together and live with the resulting current flow in the ground wire (it's a 50-amp circuit, and the ground wire is pretty hefty). Can I get away with it, or am I missing something?

  • #2
    I'm sure it will work, provided there are no GFI devices in the way, but then if someone pulls that 'safe' ground wire off the buss and latches onto it there could be trouble. The expected load may be small, but it only takes a few milliamps to ruin your day if they take the right path through your bod.

    I don't know your situation, but you wouldn't need to run a neutral all the way to the service, just go up the wall and join the nearest available neutral. I don't know whether that meets code or not, but it would be good enough for ME!
    Last edited by chipmaker4130; 03-07-2017, 02:44 PM.
    Southwest Utah


    • #3
      Electric clothes dryers were wired that way for ages. Mine still is. The 120v motor & timer run off 1 leg & ground. Just do it & don't tell anyone.
      Last edited by Bob Engelhardt; 03-07-2017, 03:00 PM.


      • #4
        Is there an installation/operators manual?

        A 115V, step down transformer sounds like an option. In any case, it is probably a safer option than running a neutral from a nearby box. That neutral could already be maxed out. But I would try to check the manual first. In any case, do insure that the safety ground IS CONNECTED.

        One more thought. One side of your 115V control circuit is already internally connected to the 230V feed: you can not and should not change that. If you add a step down transformer, you need to be sure that one side of the secondary is connected to that same side of the 230V line and that the other side of the secondary measures 115V to BOTH legs of the 230V line. Make this check BEFORE connecting it to the neutral in the oven. If it is backwards, you will read 115V to one line and about 345V to the other. If it is backwards, reverse the leads on either the primary or the secondary, but not both. Then check again. This check could prevent some accidental smoke.
        Last edited by Paul Alciatore; 03-07-2017, 03:41 PM.
        Paul A.
        SE Texas

        Make it fit.
        You can't win and there IS a penalty for trying!


        • #5
          Originally posted by alsinaj View Post
          ..... My 220VAC outlets are 3-wire, and running a neutral wire back to the breaker box isn't an option. ...
          Well, YES IT IS and option. You are just choosing not to USE that option.

          That used to be code, it isn't any more, so it is "illegal" in most locations. And there is a point to that. It never was anything but a make-shift connection to begin with.

          Your shop, your choice.

          Keep eye on ball.
          Hashim Khan


          • #6
            I enjoy thinking outside the box.

            First of all if its "like new" its probably worth too much on the resale market to ruin into a powder coat oven, so sell it to someone who needs to cook dinner and buy an older clunker that has a 3-wire connector and spend the profit on beer or finest leaded steel or whatever floats your boat.

            If you want to play with wires and ovens there are multiple kits on Amazon of PID, thermocouple, and SSR that can completely gut the 110 volt components out for a bit over $30. I have no experience with parts that cheap. What I do have is experience with 00s era cheap electric ovens and honestly the temperature control is barely good enough to bake cakes and cookies on a good day, somewhat unevenly of course, so its possible for a cheap PID to do worse but it would almost take work to do so. Of course if you want to powder coat stuff, not gut and rewire ovens, then this is not the option for you. Just remember the price of $30. I'm too good at hand soldering surface mount components (brag brag) to justify it but I've been planning on converting a toaster oven into a SMD reflow oven for about forever.

            Are you sure the components are 110 and the neutral is connected to anything but the light bulb? I've seen an old stove where the only thing that was 110 was the oven lamp and there was a wiring diagram to hook the oven lamp up for 220 service using a 220 bulb for countries that use 220 and don't have 110. I donno if everyone uses edison base sockets maybe that was part of the conversion kit. Speaking of conversion kits the euro conversion kit for that range MIGHT (emphasis might) be cheaper than the $30 rip it all out and put in a PID controller. It might be as simple as a little plug in thingie that rewires the oven light or as expensive as a whole new control board.

            You say you can't run 4wire service back to the breaker box but "can't" and machinist don't mix often, just saying. Thinking outside the box if you justify it as wiring for a new welder it might be cheaper to install a 4-wire "someplace else" like 3 feet from the breaker box so its cheap, even if its too expensive or impossible to re-wire the 3-wire at the existing location.

            If you like messing with wiring you could run the whole stove off 110 if you're careful. Its not going to heat up fast, but WRT scorching the powder coat, isn't that good? I mean you really don't want powder coat almost touching a red hot element, right? You're never going to broil a steak with it again, but isn't powder coat pretty low temp and mellow? If it takes 20 minutes to heat up instead of 5, does it matter if the conversion was basically free? If half the voltage is a quarter the wattage doesn't that mean that a 3000 watt 220 heating element would be coasting along on a regular 110 volt plug at 750 watts? This is probably an effective way to get electrocuted if you have absolutely no electrical skills but it is after all completely free.


            • #7
              Every oven I've looked at/worked on had a diagram inside for hooking up either a 3 or 4 wire cord. Normally they'll have a small connector to tie the 3rd and 4th lug together when using a 3 wire cord.
              My stove is a 2014 model, and was a lot easier and cheaper to buy a range cord than to rewire the outlet.


              • #8
                If this is an EXISTING setup, the wires have existed for a long time, then it is permitted under section 250-140.

                I took it that this was a new installation, as it seems to be re-purposing a range for powder coat. In that case, it would need to be 4 wire per NEC.

                Keep eye on ball.
                Hashim Khan


                • #9
                  I wouldn't hesitate to hook it up in a New York minute. You will be using the oven under controlled conditions; it isn't like you are going to set it and walk away for a day and a half. I'll wager the only part of that unit that uses a neutral is the timer and oven light. Stoves and dryers have run their 120 volt controls on the ground wire for scores of years- almost as long as consumer electricity has been around.

                  For some reason everytime we get into a new code, the old ways are suddenly evil. All our houses are going go up in smoke. Everything that doesn't comply with the latest code is going to burn to the ground. Bull.

                  If you are a business, you should follow code. If you are building a new shop or house, you should stick to code. If you are a professional electrician doing it for profit, use the code book. If you are going to experiment with a powder coating oven, or design and build a better mousetrap, just make sure it is safe. Safe and code are two different things.


                  • #10
                    Thanks for all your replies. To answer some of your questions: my wiring is already installed, the outlets are far from my main panel, and running a new branch circuit through multiple walls and ceilings would be (much) more work than hacking the oven wiring or building a 3-wire oven from scratch; I have all the original documentation, and there is no mention of converting 4-wire to 3-wire; the top burner controls are mechanical, but the oven has an electronic control unit - the wiring diagram just shows a big box with lots of connections and no hint of internal workings; the oven light and the cooling fan relay work off one leg of 220, the cooling fan works off the other leg, and it's impossible to tell which leg the oven door latch motor works off of. I bought this oven because it was cheap and I want to powder coat parts, not build an oven. Based on all your comments, I plan to connect the oven neutral to ground, and see if the oven works. If so, I'll measure the current in the ground lead, and if it's low, I'll leave it alone. If there are problems, I will disconnect the bake and broil elements from the computer module and control them with a furnace/kiln temperature controller (<$40 from Ebay). Tally ho!