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I have a new whirlpool dbl oven with a 4 wire wiring harness-white, black, red and green. My old single oven compartments junction box (house was built in '79), has 3 wires-black, white, and copper ground. 50amp, 240v circuit. How do I correctly connect these?

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    How old is the house? Is the circuit breaker double or single? What number on the handle? What was hooked up where the new oven is going to be connected? – Tyson Nov 26 '16 at 16:00
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    Does this oven not have a power cord? Also, can you post a photo of the inside of the box where the oven-circuit terminates? Finally, where in the world are you? – ThreePhaseEel Nov 26 '16 at 16:00
  • What is the make and model of the oven? – wallyk Nov 27 '16 at 7:00
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    Can you please post a photo of the inside of the box here? If you can't post a photo here, just post it to imgur and put a link in the comments so we can edit it into the post...and we need the model # of the oven, too! – ThreePhaseEel Nov 27 '16 at 19:51
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You'd have to look at the old receptacle to be sure. If it's a NEMA 10-50, then the following is true: it is being fed by common 6/2 grounded cable.

NEMA 10 is an obsolete and somewhat dangerous receptacle family, used in the old days for ranges and dryers. It provides hot, hot and neutral - 240V hot-to-hot, and 120V hot-to-neutral. It does not provide ground.

Often, this was installed using the common "/2" cable. There's no choice to color; it's always black, white and bare. In this usage, the white is not a neutral; it's the other hot. The bare wire is the neutral. Really.

Today, a white wire used as a "hot" must be marked with tape. Back in the old days, that was not required if the usage was obvious.

I would make the argument that the old circuit is "grandfathered", which it is. If the 10-50 receptacle broke, you could change it without breaking the grandfathering; in fact the stores sell 10-50R's for only that purpose. I would argue the same is true for changing it to a modern 4-prong NEMA 14-50. I would then use the NEC 2014 rules which allow retrofitting a true ground. Can't promise you the inspector would agree.

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It appears that you might be trying to add a 240V appliance to a 120V supply. A 240V supply will contain Red, White and Black wires typically. The Red and Black are the 120V and the -120V lines, with white being common and bare copper being ground. The green on the appliance will match to the bare copper for Ground. This 3 way wire would have to be connected to a 2 pole circuit breaker, with red on one pole and black on the other.

Unfortunately, I do not think this appliance will work here, it appears you have only 120V supplied.

  • You're likely making an incorrect assumption. It's probably old, 2 hots and bare neutral, but that might also be an incorrect assumption, I'll ask a clarification question or two above. – Tyson Nov 26 '16 at 15:59
  • Interesting thought on the 2 hots and bare neutral. I guess there wouldn't be a proper ground in that case? – trip0d199 Nov 26 '16 at 16:34
  • A long long time ago this was fairly common for an oven. Heating element and thermostat neither required neutral, if there was a clock it often had a 240v motor. – Tyson Nov 26 '16 at 16:45
  • @Tyson, black, white and a bare copper ground for an oven suggest 240V, NOT 120V. The bare copper IS NOT a neutral, it's a ground. This was not always common, it was usually an incorrect installation. This is unless the cable in question was SEU cable, then the bare braided conductor is a neutral and not a ground. – Speedy Petey Nov 27 '16 at 19:51
  • @SpeedyPetey 240 not 120 was the point of my comment, I was actually became confused about whether the bare copper would be considered neutral or ground as in a main panel it would land the same place, I tried to look up if it would be a neutral or ground as I was writing the comment but the results were not conclusive from 5 minutes of googling, saw it labeled both ways... Anyway my point was to dispute trip0d199's assumption that the white was neutral and that it was 120v 3-wire circuit. As far as popularity it may be regional but every 70's era in-wall oven around here is exactly that.. – Tyson Nov 27 '16 at 20:17

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