I’m installing a new induction cooktop to replace an old electric coil unit. The new unit has a three-wire connection (black & red hots and a green ground) with instructions for retrofit to existing three or four wire box connections (with or without a neutral wire). House was built in the 1970’s.
The old cooktop was connected with black & red hots, a white neutral and a ground to the junction box (which does not have a ground wire back to the panel but may have a ground path via the conduit – but I don’t know for sure), so it’s kinda in-between the cases in the instructions (both assume there is a grounding wire).
My initial thought was to hook up red-red, Black-Black, green (cooktop ground)-white (house neutral) roughly in-line with the four-wire retrofit instructions. Would this be my best (safest) bet or would it be advisable to attach the cooktop ground to the junction box (although I’m not sure how I ensure the box is a good ground) and cap off neutral? I suppose I could also attach the house neutral and cooktop ground to the junction box grounding screw as a “belt-and-suspenders” approach but I don’t know if that introduces other risks?
Best Answer
We haven't heard back from OP, but I suspect what's going on here is that the range uses metallic conduit all the way back to the panel, and the conduit is the ground, accessible via the green #10-32 screw in the metal junction box. That's a legal setup; OP is good to go.
This is a modern range which does not require a neutral wire. Historically neutral was used for nothing but the oven light and the clock, so it's not hard to get rid of. If there's a neutral in the supply cable, it should be capped off.
In the off chance this is an obsolete 3-wire circuit with a cable, if the neutral wire is a bare wire, it can be permanently converted to a ground. This is irreversible. Inside the panel it would need to be moved from the neutral bar to the ground bar (on a main panel they are probably the same bar). A white neutral wire can never be converted to a ground.