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I have a fairly recent house though I am not the original owner. I'm about to finish the basement, and am trying to determine if there is remediation needed for future up-stairs kitchen upgrade before finishing the basement -- which will make running new cable much harder. Specifically, wanting to ensure I would be able to replace the current gas cooktop with an electric induction cooktop in the future. Given the cooktop size I'd be looking at, 40 amps would be enough. So...

I just discovered/noticed that there is already a 40amp breaker in my main panel that is labeled Cooktop -- it's been turned on until just now. When I go look in the cabinet under the current cooktop, I found a double-gang size junction box. Opening it up, I find three pretty large wires plus ground: black, red and white wire, all neatly capped off. I can't actually see the color of the cable sheathing either at the junction box or in the walls due to obstructions. (I probably could see it if I were take the panel cover off but rather not do that.) And the inner wires' insulation have no obvious markings. Taking a cap off shows the wire is silver and stranded. Measuring one of the conductors in the box shows that it's almost exactly 1/4 inch width including the insulation.

(As you can see in the pictures, there is a separate ordinary 15amp-style receptacle next to this junction box that the current gas cooktop is plugged into. It is not controlled by the same breaker.)

Can anyone make a reasonably confident visual identification at what kind/size wire I have? Is it in fact sufficient to put in a cooktop that requires 40 amps?

Picture of box Cable Measurement Conductor closeup

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  • If you haven't finished the basement yet, you should be able to find a section of this cable in the basement you can read the writing on the jacket of. Depending on cable type, it might be rated higher than 60°C and that would permit up to 50A
    – Ecnerwal
    Jul 8, 2023 at 20:42
  • You would think so but I can't figure out how that cable is getting to the box. I can't find it going up through the floor where I would expect it to. And the whole rat's-nest of cables above the main panel is obstructed by insulation and duct-work, and I don't see anything obvious coming out the other side. Jul 8, 2023 at 20:55

1 Answer 1

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6 AWG has a nominal diameter with insulation of about a quarter inch, and is also the correct size of aluminum wiring for a 60°C rated cable to carry 40A, so you appear to be all set.

Incidentally (and this may matter to you later) that is not a double-gang box. It's a 4 x 4 or 4-11/16 x 4-11/16 square box.

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  • Ah. Thanks for the correction. I'll actually have an electrician do any hook-up. Just trying now to make sure nothing needs to be done before the basement ceiling becomes inaccessible. Jul 8, 2023 at 20:48

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