Really struggling to find a 30A electric cooktop, most of them are 40A and we have the Jenn Air JEC9530 that is running on two #10 wires to a double 30A breaker.

I finally found a cooktop that says it only requires 30A, but the manual says it must be run on #8 wire.

I do not know what I should do, the electric line for my cooktop runs from my kitchen through the foundation all the way to (who knows where) before finally ending up in the breaker box on the far side of the garage wall.

Edit: I just looked at the serial plate for the JEC9530 and it says 7.5kW which should be a 40amp breaker right? Yet it's running on a dual 30A breaker with #10 wire...

Edit 2: We are looking at two cooktops, G9CE3065XB or LCE3010SB. I found a manual that states the G9CE3065XB will run on a 30A breaker fused at both ends but the manual still says #8 wire. Here's a link to that manual, search for G9CE3065 https://www.homedepot.com/catalog/pdfImages/81/816870c8-4d4b-431b-916f-6ad03d647630.pdf

  • Do you have a make and model for your proposed replacement cooktop? – ThreePhaseEel Nov 30 '17 at 4:25
  • Yes, I'm looking at two of them... G9CE3065XB or LCE3010SB. – Brad Nov 30 '17 at 4:36
  • Give it up. Run the heavier wire. In the end you will be glad you did. – Paul Logan Nov 30 '17 at 5:11
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    @PaulLogan Do you have any idea what one could expect to pay to have a new wire ran? House was build in 83 with the island and my guess is a gas cooktop. Somewhere it was replaced with an electric cooktop and so either the wiring is original from 83 or it was re-wired when the new electric cooktop was installed. I don't want to rip up floors. – Brad Nov 30 '17 at 5:21
  • Hard to say what this would cost but if I were to throw a dart at the wall, I would say $800 to $1000. – Paul Logan Dec 1 '17 at 0:17

Cooking appliances are a bit weird

The NEC treats household electric cooking appliances (ranges, cooktops, ovens) somewhat differently due to their rather uneven loads. This starts in section and table 220.55 of the NEC, which applies an 80% demand factor to the load of a single household cooking appliance rated not more than 8.75kW. As a result, your JEC9530's nameplate rating gets this factor applied to it, causing it to be considered a 6kW cooktop for the purposes of load calculations, as 220.14(B) invokes 220.55, and 220.10 invokes 220.14 in turn.

From here, we divide by 240V to get 25A for the maximum demand load of the cooktop, then apply 210.19(A)(3) to allow us to use 10AWG wire and a 30A breaker, as the conductors only need to be large enough to serve the load, with no 125% continuous load adjustment in sight.

  • If the new cooktop is rated 7.7kW does that factor still apply and allow us to use 10 gauge and the 30 amp breaker? I tried to decode those charts but I'm not 100% sure. – Brad Nov 30 '17 at 12:51
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    What @ThreePhaseEel is trying to say is that the NEC allows diversity to cooking appliances. So 7700w/240v = 32.08 amps. If you use the allowed diversity 32.08*.8 = 25.67 amps and that amperage can be used on a #10 and 30A/2P breaker. The real question that we can't answer would be how do you intend to use this cooktop? Does your family use three to four burners two or three times a day or usually one or two most of the time? We can't answer that question you have to. Keep in mind that the NEC is a "minimum" requirement. – Retired Master Electrician Nov 30 '17 at 22:21
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    So do you want to run a fully rated feeder to your cooktop or can you live with a derated one? Also don't feel embarrassed about trying to decode 220.55 most journeyman have trouble doing it. Anyone who has graded their tests can tell you that. – Retired Master Electrician Nov 30 '17 at 22:25
  • @RetiredMasterElectrician We generally only use a single burner for dinner, sometimes 2. I can't think of anytime we have used 3 or even 4 burners at once... But the kicker is, if we did ever use 3 or 4 (say we had a gathering), we'd be at risk of a fire, right? Is that risk only if the breaker failed, or even if it didn't... – Brad Dec 1 '17 at 13:36
  • @Brad -- that risk is only if the breaker doesn't do its job. A properly functioning breaker will protect against an overload of the circuit. – ThreePhaseEel Dec 1 '17 at 23:13

I finally found a cooktop that says it only requires 30A, but the manual says it must be run on #8 wire.

The owner's manual is incorrect. Even if it draws the full 30 amps then #10 AWG copper wire is sufficient to handle the load.

The National Electrical Code is the controlling document in most areas of the USA. According to the NEC, only refrigeration equipment (A/C, heat pumps, etc.) can have a Branch Circuit Selection Current rating on their nameplate that overrides the amperage draw rating that the equipment is labeled for.

Therefore if the equipment is labeled for 30 amps then the owner's manual is wrong about the wire size. It's just that simple.

Good luck with your project!

  • I would agree but usually on a/c and heat pumps they use larger breakers to allow starting than the wire would normally handle because in rush is so high, I am a bit more cautious on stoves but in this case in my own home I would go with it even with all 4 burners on there is a safety factor in the wire size most don't know about. – Ed Beal Dec 1 '17 at 20:25
  • Right. Manuals are usually written to cover all cooktops of a certain type. That means there scope is generic and directs you to cover all of the tops the manual was written and maybe even a little more. – Retired Master Electrician Dec 2 '17 at 14:16

Brad, to try to answer you question regarding cost, I will say this: I suspect that the cost, if you have to hire is done will be significant. However, I believe that we as electricians have jobs that break down as follows: First we are to get your new appliance working according to the manufacturers instructions. Second we are to do this at a fair and reasonable price for both of us. But third and not the least important, we are in this process, obligated to protect you house and family from any unnecessary risk of fire.

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