My home currently has wiring that consists of one Black, one White, and one Bare conductor. I am installing a new cooktop w/a downdraft. It has one Black, one Red, one White, and one Green conductor. The White and Green wire seems to be bonded on the end. How do I wire this?

  • What is the voltage? is it 120 or 240 of the original circuit. Next what is the amperage / wire size? For existing wiring that may be wired 220 on the black / white conductor and the amperage is the same or less you would tie black to black and white to red then your white and green combo to the green.
    – Ed Beal
    Mar 9, 2016 at 19:48
  • Sorry forgot to mention, 240vac, 10 solid maybe 8. Old unit did not have any extras on it. One before that one also had a down draft that is covered right now.
    – user51249
    Mar 9, 2016 at 19:52
  • Please double check the wire size and voltage it's punched down to in the panel. This is very important. Mar 9, 2016 at 22:45

1 Answer 1


Assuming you're in the US. If the new cooktop has three conductors, that means it has components that run at both voltages (120V and 240V). Most likely, the heating elements run at 240 and the downdraft fan runs at 120.

Your existing circuit, because it has only black and white conductors, is wired for either 240V or 120V. You cannot power your new cooktop from this existing circuit, so you will need to install a new circuit breaker and run a new cable.

You should also identify what the cooktop requires in terms of current. It will need to be served from an appropriately sized double-pole circuit breaker using appropriately sized wire. Building code may also impose minimum requirements for service to an electric cooktop in excess of the manufacturer's requirements, so check with your local building authority if you're uncertain.

Finally, the bonding of white and green wires in the cooktop is not advisable (edit: and per comments below is not allowed edit 2: may be allowed for replacement appliances installed on previously compliant circuits). This may be an option the manufacturer recommends when a proper ground is not available, but shouldn't be applicable in your situation as your new circuit will carry a ground (bare) wire.

  • Not only is the bonding of the neutral and ground not advisable, it is no longer allowed by the National Electrical Code for ranges and dryers in new installations. I don't think it was ever allowed for cooktops.
    – ArchonOSX
    Mar 9, 2016 at 20:07
  • Oh, I'm afraid it was. It is a terrible practice. A lost ground/neutral guarantees shock. Mar 9, 2016 at 22:42
  • 2
    @ArchonOSX, it was and still is allowed for replacement household cooking appliances and dryers. There is still an exception for previously complaint existing circuits. For instance, if this circuit were run in SEU cable they would be allowed to connect the new 120/240V cooktop to it with the ground bonded to the neutral. ....See NEC 250.140 Mar 9, 2016 at 23:23
  • 1
    Ahh, yes I see it says "counter-mounted cooking units" in Article 250.140. I knew of the exceptions for existing range and dryer circuits. Thanks for the tip.
    – ArchonOSX
    Mar 9, 2016 at 23:38

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