Using 3 wire (2 hot and 1 bare copper wire) for new replacement oven

Question

We are installing a Wolf dual fuel stove to replace a Dacor. The existing wiring is 3 wire (black, white, and bare copper, see photo). Breaker service is 30amp (C-H panel) and Wolf stove specifies 30amp. The installer will use a 40amp 3 wire oven cord. We plan a 3 wire receptacle. I need guidance how to wire the receptacle. Thank you.

Please refer to similar post on this topic.

Random text I cut-and-pasted for no good reason and without explanation. Maybe some StackExchange volunteer editor will fix the formatting for me LOL.

Electrical Connection.

The terminal block on the back of the range allows for a 3-wire or 4-wire installation. Remove the terminal block cover to expose the screws with corresponding numbers.
Route the wires through the strain relief and to the terminal block.

THREE-WIRE INSTALLATION

1. Move the metal ground strap to positions one and two. Refer to the illustration below.
2. Connect green/ground to position one.
3. Connect red/L2 to position three.
4. Connect black/L1 to position four.
5. Tighten the screws on the strain relief and install the terminal block cover.

FOUR-WIRE INSTALLATION.

1. Remove the metal ground strap.
2. Connect green/ground to position one.
3. Connect white/neutral to position two.
4. Connect red/L2 to position three.
5. Connect black/L1 to position four.
6. Tighten the screws on the strain relief and install the terminal block cover.

Wolf allows 3 wire installation. If a power supply cord is used, the cord must be designated for use with ranges and rated for 240 V, 30 or 50 amps (refer to the chart below), and must include 3 or 4 conductors. A 4-conductor cord is required for installations where grounding through the neutral is prohibited. Performance may be compromised if the electrical supply is less than 240 volts.

 ELECTRICAL REQUIREMENTS—SINGLE OVEN
 Electrical Supply grounded, 240/208 VAC, 60 Hz
 Service 30 amp dedicated circuit
 Total Amps 21
 Max Connected Load 5.2 kW

Answer 1

A ton of conversation in comments, information conflicting between Wolf customer service and the installation manual, etc. To summarize, there are really only two valid possibilities:

Oven needs neutral

If this is the case then:

• The oven will not work properly if the two hots and ground are connected and no neutral/ground bond is used.
• The oven can not be installed legally, since this is a 2001 build, without running a new cable that includes two hots, neutral and ground.
• If the oven were installed using neutral/ground together (using the neutral/ground bond) with the existing cable (bog standard 10 AWG /2 with bare ground) then it would be "neutral on ground" and not legal or safe.

Oven does not need neutral

If this is the case then:

• Installation using two hots and ground is OK.
• Neutral/ground bond must not be used, but would not matter because neutral not used.
• The installation manual would be wrong.
• The neutral connection on the oven would be superfluous, as would the neutral/ground bond.

My working theory is that everyone at Wolf who has said "this is OK" is treating it as a pre-1996 build with neutral and no ground. But OP has stated it is 2001 (at which time this was long deprecated and no longer permitted) and it is very clearly a modern /2 NM cable, not an older type with bare neutral.

YOU CAN'T DO THAT

You need to get a 240V-only oven that doesn't use neutral, or run a new cable.

The allowance for 3 wire is when you have neutral but no ground. You have ground but no neutral, so the exception does not apply. This is not a stripped wire, it is a bare ground by design. There are cables (much older or much larger) with a bare neutral, but this is not one of those. This wire may be connected to the neutral bar in the main panel, which is OK, but that doesn't make it a neutral.

The whole "3-wire vs. 4-wire" issue with ovens (and clothes dryers) refers to going back to ye olden times when there was no ground wire in most circuits. It was changed over time, but by 2001 it was definitely not legal for new circuits (whether in an old or new house). It only remained legal (and in most, but not all, places remains legal to this day) for straight replacement. That is, if you had a functioning 3-wire-no-ground circuit and the receptacle or plug goes bad, you can replace it with an identical one. If you had an oven using such a circuit and you need to replace it, you can attach the same 3-wire plug to it. But if you have to upgrade the circuit (30A to 40A) or move the circuit (e.g., renovate kitchen) then you need to switch to a proper 4-wire circuit.

There is an entirely different "3-wire" circuit which has two hots and a ground. That is 100% legitimate for new installations. But it only provides 240V (or 208V in some places) and not 120V.

What did you have before? If it was installed properly, you had a 240V-only oven. If it was installed improperly, you had a 240V/120V oven with ground being used as neutral/ground and were living dangerously. But you can't repeat the old mistakes.

The plug/cord you linked actually says on the description page:

• The 3-wire cord fits most homes built prior to 1996

That should have been a clue that there was a problem, since your house was built in 2001.

But there is an additional problem. The cord/plug is for a 40A circuit. The receptacle (and therefore the plug) for a 40A circuit is the same as for a 50A circuit but is different from a 30A circuit - which I verified, the Leviton receptacle you linked is for a 50A (which allows 40A as well, but not 30A) circuit. You can't put a 40A/50A receptacle (which is needed for a 40A plug) on a 30A circuit. Your wires are almost certainly 10 AWG which is not large enough for a 40A circuit. So even if you could use a pre-1996-3-wire plug/receptacle/circuit (which you absolutely can NOT do), you would need a different plug/cord/receptacle to make it all work.

I actually highly recommend hard-wiring rather than plug/cord/receptacle. That does not change the basic "need a neutral, need 4 wires" issue. But at least it eliminates the plug/receptacle compatibility issue and removes one common point of failure. Unless you plan on moving your oven a few times a year, plug/cord connection does not provide any benefits.

---

And another possible problem, as suggested in another answer, but I'll elaborate a bit. Those wires don't look all that big. They might be 10 AWG. But they might be 12 AWG or even just 14 AWG. If they are 14 AWG or 12 AWG then you aren't just cooking with gas, you're playing with fire! And if that's the case, here is my plausible scenario:

• Home originally (2001) had a simple gas cooktop/oven combination. That uses 120V 15A (14 AWG) or 20A (12 AWG) circuit to power timer, light, gas ignition, etc. Only actually uses a couple of Amps. And not just "only gas" but probably "bottom of the line bulk order builder special".

• Owner decided to upgrade to gas cooktop + electric oven, a.k.a., dual fuel. Those get expensive, but they are nice. I've got the poor man's version of that (relatively speaking) - a separate gas cooktop (which replaced an electric coil cooktop) and electric wall oven. So I definitely sympathize - I am firmly in the "gas for cooktop, electric for oven" camp. But as you found out, it isn't easy to run a new cable. So the owner cheated a bit. Or rather, a LOT:

  • Upgraded breaker to 30A without replacing the cable. Meaning wires are undersized, leading to fire potential.
  • treated hot/hot/ground as if it were hot/hot/neutral and then combined ground and neutral. Very much against code, as I have already described.

But everything worked, the house didn't burn down, and now you are ready to replace the oven. And now you really need to fix this. Maybe the previous owner had the oven more for show, but when you get Thanksgiving dinner going with non-stop oven for turkey, pies and everything else, those wires will show their limits...

Answer 2

That /2 cable was never legal

Starting in 1954 they started requiring these strange new things called "ground wires" to be added to circuits. By 1966 they were required on all circuits. EXCEPT: this would render obsolete huge investments in stocks and investments in #10 and #8 SEU (black, black, bare mesh neutral) and several sizes of NM "/3 no ground" (black, white, red) cables. The appliance industry also disliked the change. The compromise was dryers and ranges could continue using groundless connections to "use up" these old stocks of cable, at which point the only legal cables would be "/3 with ground" type and everyone would just use that, right?

Unfortunately many electricians and some inspectors rebelled against this "grounding revolution" and used "/2 w/ground" illegally for dryers and ranges. That is what you have. It was illegal the day it was installed, and age has not made it any more legal LOL. The bare ground is not insulated well enough to be neutral.

The answers you link are not applicable because they use SEU cable in a way which was legal pre-1996, and is thus grandfathered today.

If only someone made a range that didn't need neutral!

Well, ranges don't need neutral, except for a 120V Edison socket for an oven light. Why is that an Edison socket? Because up til the 00's, every house stocked plenty of 20 cent incandescent bulbs fit for use as an oven light, so why make people buy something special? Oh right, all the kids being killed by the dangerous 3-wire no-ground dryer and range connections.

The concept is irrelevant anymore. Since people must go out and get a specialty oven light anyway, I would expect manufacturers to just drop the neutral requirement. I await with bated breath, as do many still-alive children. When that happens, your /2 will be legal for a range.

(SEU cable, you're allowed to re-classify the bare neutral as a ground; "/3 no-ground", there's a procedure for removing the insulation from a wire to make it ground).

The question is whether the Wolf requires neutral.

They say it doesn't need neutral, but this area is rife with misunderstanding, "very convenient misundertanding", and outright deception for the sake of appliance sales.

Manassehkatz had a brilliant idea. Wire it up using the 4-wire instructions, and connect neutral to nothing. That will put the truth to the lie. If it works, you're all set. If stuff doesn't work that you can live without, likewise. Otherwise test-connect neutral, and if the broken things come to life, they lied LOL.

Answer 3

I would suggest hiring an electrician to run a new wire to the new stove for a few reasons:

1. It's not clear whether the wires are 10 gauge, as required for a 30-amp circuit. (Nowadays, most 10 gauge wire has an orange sheath, but it may not have been that way when your house was built in 2001.) You should read the printing on wiring sheath or check the wire thickness with a electrical tool. Using AWG 12 or 14 with a 30 amp breaker is definitely a significant fire risk. EDIT: In a later comment you confirmed that the existing wire was indeed 10 AWG.
2. Two of the tabs have been removed in the back of the blue box, meaning that the existing cable may not be clamped properly. (The tabs are supposed to prevent the cable from being pulled out of the box.) Plastic electrical box tabs - ok if broken?
3. The blue box is a single-gang size, but the receptacle that you linked to says "Do not use with single-gang wallboxes, single-gang mud rings or single-gang box extenders." I am pretty sure that most larger receptacles require a 2-gang square box so there is enough space to connect the thick wires.
4. As others have mentioned, a separate neutral and ground is required by many appliances and most electrical codes. (Although reading through the chat, perhaps not for this stove?)

Do you really want to risk damaging your new stove to save a few dollars on wiring?