Wire Size for 35 Amp Cooktop

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Old 10-02-17, 08:17 AM
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Wire Size for 35 Amp Cooktop

I just installed a sub-panel for a basement kitchenette (thanks for the help on that!). I had installed a 30A circuit breaker for a cooktop, on a 10/3 (orange NM-B) wire which is maybe four feet long as the panel backs right to the cooktop area.

However the cooktop I just bought specs at 6000W/220V, waiting to hear back on the Amp rating from the manufacturer, but did find one web site that lists it at 35A, so I am assuming that is the required rating.

So, given 35A rating, but currently 30A CB and 10/3NM-B wire...Any experts out there can give me advise on the following:

1. Change the breaker from 30 to 35A?
2. Change the wire? New wire size?

Extra info: It's really not a huge problem to change the wire at this point, other than the hassle of bending big wires in the relatively small space of the sub-panel (and the $$). Also, if it matters, this cooktop will get used maybe a couple of times per year--but who knows 10 years from now. I tried working my way through the code but didn't quite know which case I fall under.
 

Last edited by orca15; 10-02-17 at 08:33 AM.
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Old 10-02-17, 08:24 AM
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I've got 10 feet of leftover 50A NM-B laying around if that helps but man is that stuff hard to work with! I'd just as soon buy something smaller but maybe I should future-proof it? Will be covering up the panel area with drywall someday soon. But the whole panel is fed with a 50A wire and CB so probably don;t want to go much bigger than the 30 or 35A cooktop I have planned.

Oh, and to be clear, the panel and cooktop are on either side of a framed wall with the cooktop side now drywalled and the panel side still open
 
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Old 10-02-17, 08:27 AM
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6000 watts 240 = 25 amps.
 
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Old 10-02-17, 08:35 AM
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Right, I did that math, but was concerned with the rating...not sure why they rate it much higher than it seems to need. Oh, and it has 4 2000W burners (specifically [email protected] and [email protected]) so one more twist.
 
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Old 10-02-17, 09:42 AM
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What do the instructions or data plate call for?
 
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Old 10-02-17, 02:29 PM
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Don't have the cooktop in hand. Haven't heard back from the manufacturer. The only thing I've seen was one website (out of 5) that said 35A, the others were silent on the issue.
 
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Old 10-02-17, 05:22 PM
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Sears and Kenmore use the voodoo magic formulas too.

At this point I would seriously consider using #8 cable..... probably on a 40A breaker.
You couldn't put the #10 on anything over 30A.

Just a cooktop will come with a metal clad whip with wires in it that gets connected to a junction box. You could use your 50A cable to that junction box where the wires will need to be spliced anyway.
 
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Old 10-06-17, 05:17 AM
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The manufacturer sent me the manual--which didn't have an amperage but called for 7200W. Later they replied that it needed a 35A circuit.

So the answer is 35A, I guess. Sounds like #8 wire?
 
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Old 10-06-17, 08:43 AM
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Recap:

New construction (basement upgrade) already wired for 30A cooktop (30A breaker and 10/3NM wire). 100A subpanel just a couple feet away powered by 50A breaker up in the main panel.

Manufacturer of the cooktop I ended up getting says 7200W but needs 35A circuit. Easy access to change wiring right now.

Solution:

Current suggestion is to change the 10/3 to 8/3 NM and install a 40A (why not 35A?) breaker.

Should I do the wire then wait to see if the 30A trips before going higher? Not that I am worried about the $20 for a new breaker...

Copy all on the junction box- had that planned - assume it goes outside the drywall and screwed to a stud. I haven't worked much with metal boxes but I am sure I can figure it out. Assume I should pigtail a ground to the box.
 

Last edited by orca15; 10-06-17 at 08:58 AM.
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Old 10-06-17, 09:42 AM
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To make it easy on yourself, I would go ahead and run 8-3 w/ground on a 40A breaker. The cooktop will be either 3-wire (most common) or 4-wire (neutral inside whip).

Yes, you need to secure the house ground to the box and to the appliance bare or green wire. If the cooktop has a ground wire only, cap off the neutral in the box. The whip doesn't include a strain relief, I use a 1/2" flex 90 connecter.
 
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Old 10-06-17, 11:28 AM
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OK got it. Glad you told me about capping off the neutral or I would have been staring at it with a puzzled look for a while. Manual says L1-L2-PE which I take to mean "protective earth" so assume it will be three wire as you describe.
 
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