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Booron 12-06-2009 04:27 PM

Cooktop wiring upgrade
So I got a great deal on a new 50A 36" induction cooktop and planning the wiring is, expectedly, getting a little hairy. The current setup is 2 30A circuits feeding the old 30inch range and separate wall oven. Both of these circuits are wired with 10AWG and they both run through 1 1/2 inch steel pipe which stretches between the fusebox (I'm calling the guy back tomorrow to accept his bid on the upgrade and I would like to have this wiring in place before he begins) and the area in the basement below the range and oven. From here they connected 1" conduit which runs up into the floorboards and behind the rear of the cabinet between the pipe and an the old steel j-box. This house was built in 1958 and everything in it is grounded through the metalwork, i.e., the old cooktop has two hot wires, a neutral, and a ground, but the circuit only runs two hots and a nuetral; the ground is simply screwed into the j-box and not wired back to the fusebox. Now I'd ideally like to future proof my kitchen for the day that I get a new wall mounted oven which will most likely exceed 30A so I was planning on making two 6-3 cable runs, ideally in the current pipe/conduit structure, or at least into the existing j-box, however the more I look into it this looks impossible. Now I just want to get the cooktop wired in as it is sitting here on my floor. Here is the latest wrinkle, the new cooktop has no neutral.

So here is the latest plan: I'd run cable independently of the pipe/conduit and through a new hole in the floorboard and behind sheetrock (hidden by the cabinet the range sits on) into a new j-box. Since there is no neutral should I use 6-2? And if so can I satisfactorily run the appliance ground out of the new j-box and attach it to the old j-box? Do they make steel j-boxes anymore? Could I just attach the two boxes together with bare wire? Or should I use 6-2 WG and run the ground all the way back to the main?

Secondly, this plan would call for demoing some unexposed sheetrock. I wouldn't mind this if I could simply replace it with some kind of wood paneling to act as a baffle for future service (i.e., the wall mounted oven). Is there any kind of restriction on this?

Incidentally every electrician I've discussed this with says to just connect it to the old 10AWG wires as they claim I'll never come close to 50A with the thing?!

Any criticisms would be greatly appreciated.

Jim Port 12-06-2009 05:03 PM

If you run a new cable back to the panel it will contain a ground. If you run a -2 cable the appliance must be 240 volt only. If it is 120/240 it will require a neutral and would need a properly sized 3 conductor cable plus ground.

You need to install a circuit rated to meet or exceed the amps required by the cooktop. Electric stoves with ovens are typically wired with a 40 or 50 amp circuit. I would not go with the excuse that you can use #10 on a 50 amp circuit. NO. 10 has a 30 amp limit.

Scuba_Dave 12-06-2009 05:18 PM

Don't listen to them, #6 is required for a 50a setup
The time you will use a lot of power is times like Thanksgiving when you have a turkey going & all 4 burners

I'd be inclined to run a 6-3 in case the cooktop is ever swapped out for one that has a neutral
Cables are not required to be in conduit
Individual wires are required to be in conduit
Ground must run all the way back to the panel, new cable will have that ground

300zx 12-06-2009 05:54 PM

Just like everybody is saying you need a 50 amp circuit #8 wire

kbsparky 12-06-2009 06:12 PM

You only need a #8 THHN wire for 50 Amps if you install it in that conduit. For the cooktop, that means you only need 2 conductors, if you use the conduit for your equipment ground. If you want a separate ground, then it only needs to be a #10.

Plenty of room in that conduit if the sizes you state are accurate.

Booron 12-06-2009 08:50 PM

Thanks everyone, sorry if my original post was convoluted! I may have to take your advice scuba, I didn't even think about that oddly enough since part of the discussion had to do with "future proofing..."

Booron 12-06-2009 09:03 PM

I pulled the wall apart and the wires are run to what appears to be a octagonal ceiling box with a cover-plate knocked out to accept the 3/4" conduit from the old cooktop. Is this acceptable? I was planning (after reading your reply's) to run 6-3WG naked up the wall into a new work plastic box if I can find one with a 1" knock out as the new cooktop requires it. Does style or material build of the j-box matter?

Scuba_Dave 12-08-2009 01:43 PM

I must have #6 on the brain...actually I have 1/2 roll left so will use that for my stove
I used #6 on my hot tub & 60a made sense to buy a roll then buy the white & green seperate

75c rated connection #8 = 50a
Old 60c rated connection (old stove or outlet ?) #8 only rated 40a

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