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I am replacing a double oven. 1974 model tappan. The new combo has 4 wires, red, white, black and green. The wall / supply is a Romex wire with white, black and bare. The new unit, Frigidaire FGMC2765PFK has the microwave plugged in to the top of the oven. How do I connect the wires for proper operation?

  • What is the wattage stated by the nameplate on the device? The manual won't say, it says "look at the nameplate". – Harper - Reinstate Monica Dec 27 '18 at 17:56
  • Is the supply run from the main panel, or from a subpanel? How hard would it be to pull a wire from the panel to the oven junction box? – ThreePhaseEel Dec 27 '18 at 23:34
  • It would be nearly impossible to pull another wire. I believe it is directly from the main panel. – tony Dec 28 '18 at 1:55
  • Can you post a photo of the inside of the junction box then? – ThreePhaseEel Dec 28 '18 at 2:07
  • There is no junction box. Just a Romex wire with White, black and a bare wire.Not sure how to post a photo. – tony Dec 28 '18 at 14:28
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It took a bit of digging through the Frigidaire site, but I found the specifications page.

Key points:

Voltage Rating 240V/208V/60Hz

Connected Load (kW Rating) @ 240/208 Volts 6.9/5.2

Minimum Circuit Required (Amps) 30

and

Single phase 3- or 4-wire cable, 120 / 240 or 120 / 208 Volt, 60 Hertz AC only electrical supply with ground required on separate circuit fused on both sides of line.

  • Circuit required - it says 30 Amps. This is confirmed by the installation manual which covers many models but says for an appliance rating between 4801W and 7200W (6.9kW = 6900W), circuit recommended = 30A. This is actually a good thing as it is quite likely that the existing circuit for your Tappan was 30A or larger. If so, the wires should be OK (except for the number of wires...), though you may actually need to downsize the breaker if it is currently a 40A breaker.

  • Wires required - it says 3 or 4. However, the installation manual (see bottom of page 3 and top of page 4) makes it quite clear that a 3-wire connection is only OK if (a) permitted by local code (it is typically grandfathered in, but not recommended, and possibly forbidden for a new appliance installation, and in any case not a good idea) and (b) the 3rd wire must be a neutral - i.e., a full size insulated current carrying wire, NOT a bare ground as you currently have.

Bottom line: You need at least one new wire. New oven needs 2 hots, neutral, ground. Old oven was either:

  • 2 hots plus ground - need another wire for neutral
  • 2 hots plus neutral combined with ground - not safe

If all you need to do is add one wire and the existing wires are in conduit then you can do that. If they are a cable then you will usually replace it with a new black /red /white /ground cable of the appropriate size.

If you add a wire to conduit, I believe (Harper or one of the other pros can confirm), you should actually use the existing white wire as neutral and add a different color (typically red, but anything not white, gray or green is OK) for the 2nd hot.

  • No it is not required to replace the wiring! Code allows the existing wiring to be used. The black and white are usually hot in this case. They would connect to the red and black. – Ed Beal Dec 27 '18 at 19:53
  • @EdBeal I agree, provided (a) it is in conduit (so another wire can be added), which appears to be the case based on "supply is a loose wire" and (b) it is big enough, which unless the previous oven was really wired wrong (e.g., 12 AWG), should not be a problem, as ovens even in 1974 typically used 30 A. But my understanding is that white should always be neutral in a conduit (except at really large sizes), in which case white should become neutral and a new wire should be added to be the 2nd hot (replacing white). – manassehkatz-Reinstate Monica Dec 27 '18 at 19:55
  • I have seen a lot of built in ovens that were direct wired from the romex it would look like a loose wire in that case. This was very common in that time frame. – Ed Beal Dec 27 '18 at 20:09
  • Took me a minute to realize what you meant - i.e., the existing "loose wires" might really be Romex. But if that's the case, then (normally) no conduit, in which case you can't just add a single extra wire (for the missing neutral) which means (as was the case when I replaced my single oven with a double and needed to go up from 30A to 40A), a new NM cable of the appropriate size and /3. – manassehkatz-Reinstate Monica Dec 27 '18 at 20:13
  • Since it was a double oven I would expect the wire gauge will be sufficient, then the question would be the max breaker size required by the MFG. – Ed Beal Dec 27 '18 at 20:49

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