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The original 3-prong oven plug has the normal 2-hot wires. However, I don’t know if it was a neutral or ground wire that was the third wire, as it’s aluminum and completely stripped. I’ve looked up what to do in this situation but can’t find anything anywhere to fix it. (The wiring in this house was terribly done about 60 years ago)

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  • You could take the front off the electric panel and see there whether the third wire was insulated or bare. Bet it's insulated, meaning it can be used as a neutral. Commented Mar 23, 2021 at 23:12
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    @JimStewart -- I wouldn't be surprised if it was bare Commented Mar 23, 2021 at 23:16
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    @JimStewart I'm betten it' a ground, bare
    – JACK
    Commented Mar 23, 2021 at 23:17
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    Can you post photos of the inside of the box for the old oven receptacle please? Also, is there a fridge-sized area of uncommitted wall-space near the oven location? Commented Mar 23, 2021 at 23:17
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    @JesseM -- upload your photos to imgur then post links to them in the comments here, and we can then upload them to this site Commented Mar 24, 2021 at 1:18

2 Answers 2

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This particular installation is SEU type cable - 2 black hots and one "wrapped mesh" neutral. Weird that bare is neutral, but it is with SEU.

Advice in this answer Does Not Apply to "/2+ground" (black white bare) NM or UF cable; that cable was illegal the day it was installed, and cannot be used for an appliance which needs 240V+neutral. At all.

Any 3-wire range connection has 2 hots and a neutral. There is no ground. This is a dangerous condition, because a simple, common problem with the neutral wire can cause the chassis of the range to be electrified!

If you want to install a 4-wire receptacle, there are 2 options.

Option 1. You can use a GFCI circuit breaker

This is simply a matter of fitting the appropriate breaker, then marking the receptacle "GFCI Protected / No Equipment Ground".

Option 2. You can retrofit a ground wire

This is a "simple" matter of running a #10 ground wire from the receptacle location to anywhere there also is a #10 or larger ground going back to the panel. That could be the panel itself, a grounded water heater or A/C unit, the grounding electrodes out to the ground rods, or non-flex metal conduit going back to the panel.

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  • There are some cables which have 3 wires and one is uninsulated, right? Two hots and a ground, which would be for 240 V only applications, right? I can imagine that at one time some ovens and some ranges were 240 V only, right? But I don't know if such things actually existed. Nowadays they all seem to need 120 V as well as 240 V, but once upon a time in . . ? Commented Mar 24, 2021 at 1:57
  • @JimStewart It really depends on the cable. With SE cable the bare wire is neutral. Ovens have always been 120/240V because they need to power an oven light. Commented Mar 24, 2021 at 2:53
  • So if SE cable was used (2 insul hots and 1 uninsul for neutral) could you retrofit a separate ground? Or would you have to replace the cable to get 4-wire function? Commented Mar 24, 2021 at 3:01
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    @JimStewart My reading of the Electrical Code is that a ground could be retrofit. You'd have to be careful not to let the SE cable neutral touch the ground, though. Sleeve it or something. Commented Mar 24, 2021 at 4:33
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What you likely have is Type SE cable with 2 hots and a neutral. There was a time when the NEC allowed to install just those three wires and ground your range or dryer to the neutral conductor (called the grounded conductor in the NEC). Existing 3 wire circuits that were installed when legal are still legal. See the exception portion of the NEC quote below. If UL or other lab has approved your appliance for this type of grounding then the installation instruction will tell you how to connect the ground to the neutral in the appliance and connect a 3 wire cord. Here is the applicable code section:

250.140 Frames of Ranges and Clothes Dryers. Frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be connected to the equipment grounding conductor in the manner specified by 250.134 or 250.138.

Exception: For existing branch-circuit installations only where an equipment grounding conductor is not present in the outlet or junction box, the frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be permitted to be connected to the grounded circuit conductor if all the following conditions are met.

(1) The supply circuit is 120/240-volt, single-phase, 3-wire; or 208Y/120-volt derived from a 3-phase, 4-wire, wye-connected system.
(2) The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum.
(3) The grounded conductor is insulated, or the grounded conductor is uninsulated and part of a Type SE service-entrance cable and the branch circuit originates at the service equipment.
(4) Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment.

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  • There are some cables which have 3 wires and one is uninsulated, right? Two hots and a ground, which would be for 240 V only applications, right? I can imagine that at one time some ovens and some ranges were 240 V only, right? But I don't know if such things actually existed. Nowadays they all seem to need 120 V as well as 240 V. Commented Mar 24, 2021 at 1:34
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    @JimStewart There are bare ground (UF,NM) cables that the bare ground can't be used as a neutral and don't satisfy the exception, but the Service Entrance Type SE the bare is designated as a neutral. I don't think there was ever a time that ranges (or dryers) were straight 240v. I remember the range my parents had featured a 120v receptacle on it. The grounding requirement for receptacles first appeared in 1947. Lore has it the exception to allow the underutilized neutral to be used as a ground was a WWII concession to save metal. Commented Mar 24, 2021 at 2:32
  • @FreeMan this website gives a TIA#, haven't looked hard enough to find the actual text. ncwhomeinspections.com/… Commented Apr 24, 2021 at 1:17

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