10-2 Romex for 240v appliance?

Discussion in 'Electrical Forum discussion & Blog' started by ironspider, Mar 12, 2014.

  1. ironspider

    ironspider Member

    Messages:
    69
    Location:
    Michigan
    Greetings all, we're redoing our kitchen and we're about to install a 220/240v oven that requires a 30amp dedicated circuit. I've got a lot of 10-2 ROMEX® left over from a circuit install I did in our barn workshop and I'd like to use it as it appears 10ga wire can power a dedicated 30amp circuit.

    My question is this though: The installation manual for the stove indicates that the stove has 4 wires (black, red, white, ground/green/bare). In the section about connecting it to a 3-wire system, it shows black to black, red to red, and then white and ground to *white* from the existing wire. It does not show the ground wire from the existing wire in this diagram. Sp my question is, instead of having to buy 10-3 ROMEX®, can't I just connected black to black, red to white, and white and ground (from the oven) to ground in the existing wire? Then, at the panel, code the white wire for hot and use it as the "red" as it connects to the 30amp double pole breaker?
    Last edited by a moderator: Jun 20, 2014
  2. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,523
    Location:
    Houston, TX
    You need the 3 conductor + ground. The Ground wire on 10-2 should not be used for neutral.

    The appliance most likely uses 120V as well as 240V.


    Good Luck on your project.
    Last edited: Mar 12, 2014
  3. hj

    hj Moderator & Master Plumber Staff Member

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    The "ground" in your 10/2 is a bare copper wire and is for grounding only. If you had black/white/red and NO ground, (which would be unusual unless it was a very old piece of wire or an existing cable), then it would conform to the "old 3 prong" method when the appliance neutral was bonded to the frame and also served as the ground, which is what they show when the EXISTING wiring is only a 3 wire cable. Since you are installing a new cable, do it correctly and use a 10/3/wg cable.
    Last edited: Mar 12, 2014
  4. ironspider

    ironspider Member

    Messages:
    69
    Location:
    Michigan
    Gotcha, that makes sense. Like I said, that cable was from a different project so it's not like I bought the wrong cable and now I'm screwed. BUT, speaking of buying the wrong cable, we are also putting in an induction cooktop which requires a 40amp circuit. I bought some 8ga NM which again, is 8-2 (black, white, ground). I bought this because the cooktop manual says "You must have a 2 wire, three-conductor, 208/240VAC, 60Hz electrical system. A white (neutral) wire is not needed for this unit". Now in this scenario am I okay to use black to black, red (from cooktop) to white (label white at panel breaker with red or black electrical tape), and ground to ground?

    Let me attach a picture of the installation manual picture...

    wiring.jpg
  5. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,523
    Location:
    Houston, TX
    lol.

    Made in China ?


    Sorry...
  6. ironspider

    ironspider Member

    Messages:
    69
    Location:
    Michigan
    Is General Electric made in China? If so, then yes :)

    EDIT: This is a GE PHP900 series 30" induction cooktop.
    Last edited: Mar 12, 2014
  7. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,523
    Location:
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    Your drawing says "If local code permits"

    I do not think that hook up will meet any of the new codes in USA.


    I could be wrong.
  8. ironspider

    ironspider Member

    Messages:
    69
    Location:
    Michigan
    So electrically speaking, it's fine (as this is how the old oven was wired)--but if the codes have changed and now require there to be 3 conductors (+ground) then it's going to be a problem come inspection time?
  9. Stuff

    Stuff Member

    Messages:
    53
    Location:
    Pennsylvania
    You need to ask the inspector what is allowed. If you have an existing 8/3 gauge feed you may be able to use the tap rules to power both the oven and cooktop.
  10. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,523
    Location:
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    Will it work. Yes.

    But you need to follow what the installation manual says.

    If it says it needs 3 wires + a ground, then that is what is needed. Or the inspector may and should fail it.

    If it uses 120V in any way, to control the electronics or light bulb, then it may require all 4 wires, if that is what your manual says. You should not change the plug on the appliance.


    If it only requires 240, then you should be good to go. But your manual says different.
    Last edited: Mar 12, 2014
  11. ironspider

    ironspider Member

    Messages:
    69
    Location:
    Michigan
    Right, I see what you're saying. And that makes sense to me because the oven has 3 wires + ground coming off it whereas the cooktop only has 2 wires + ground coming off it. It does have some indicator lights on it as well as a single digit power level indicator (basically a 9 segment single number)(red leds) to indicate surfaces are on. I've read that about the 120v (and it seems from the posts above that that's exactly why the oven needs that extra wire) but this cooktop only has the 2 wires + the ground.

  12. DonL

    DonL Jack of all trades Master of one

    Messages:
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    Location:
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    The cook top is a different story.

    I thought you were talking about the oven requirements.


    Carry on...
  13. ironspider

    ironspider Member

    Messages:
    69
    Location:
    Michigan
    Lol my bad DonL. No I'm for sure switching out that oven wiring and going to 10-3 on that. I just wanted to check if I was further boned on this cooktop 8-2 deal. And it appears I may be if the code has changed :)


  14. houptee

    houptee Member

    Messages:
    186
    Location:
    Monmouth County, NJ
    If you are running a new branch circuit off the panel, then you must run 3 insulated conductors plus ground.

    If the range was plugging into an existing box with a range cord, they grandfather in the existing box that has no insulated neutral, and let you use a range cord with 3 prongs vs the newer 4 prong cords. Same goes for electric dryers.

    But since your pulling new wire you will have to have that insulated neutral and the bare ground.

    Also the NEC says:

    Branch circuit conductors that supply household ranges, wall-mounted ovens, or counter-mounted cooking units must have an ampacity at least that of the rating of the branch circuit and at least that of the maximum load to be served. For ranges of 8¾kW or more rating, the minimum branch circuit ampere rating is 40A [210.19(A)(3)].
  15. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,523
    Location:
    Houston, TX

    That would depend on the appliance installation instruction.

    If it says it needs 4 wires, then 4 wires are required.

    You can not wire it against manufacture instructions.


    Well you can, but it is not recommended.
    Last edited: Mar 13, 2014
  16. Reach4

    Reach4 Well-Known Member

    Messages:
    2,836
    Location:
    IL
    http://ecmweb.com/qampa/code-qa-identification-circuit-conductors says
    So yes, if I interpret this correctly, and if tape is considered effective and permanent. Otherwise paint or heat-shrink tubing might be more permanent.
  17. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,523
    Location:
    Houston, TX

    Is this the same thread ?

    I thought the original thread was about a Uninsulated Ground wire being used as a Neutral.

    Not marking a insulated wire for 3 or 4 wire switching.


    My computer must have its wires crossed.
  18. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,286
    Location:
    Cave Creek, Arizona
    Too tedious to read all the intervening replies, and congratulations on using a induction unit. When I built this house I set it up for a 36" GE installation, but when I placed the order, they had stopped making induction tops because of a Japanese lawsuit and I had to scrounge the entire USA, until I found one in a Las Vegas company's warehouse. When I turned it on, one burner unit was damaged because it had been "knocked around" for years. Fortunately, by the time the next burner unit went bad, and the replacement would have been $1,500.00, Sears started selling them again, at a reasonable price so I replaced it. Prior to that, the only ones available were from Australia and they were in the multi thousand dollar range. But, back to your question. IF it does not have 120 volt control circuits, and it says it does not need a neutral, (mine did need one), then you only need a 2 wire with ground cable.
  19. DonL

    DonL Jack of all trades Master of one

    Messages:
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    Location:
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    I think a lot of the new imported stuff may not require 120V. 240 is easy to get just about everywhere.

    As for the wire color, Red would be best to remark the wire on both ends, for the cook-top.


    Without induction nothing would cook... Magnetic is cool.
  20. Reach4

    Reach4 Well-Known Member

    Messages:
    2,836
    Location:
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    Yes. Post #4 on the thread.
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