New 50amp Induction Cooktop On A 40 Amp Circuit? - Electrical - DIY Chatroom Home Improvement Forum

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Old 11-30-2010, 07:18 AM   #1
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New 50amp Induction Cooktop on a 40 amp circuit?

I recently had an electrician out to check my circuit. I was told I have #8/3 romex with a double pole 40amp breaker for our current electric cooktop.

New 5 burner induction cooktop:

Amp Rating at 208V: 50
Amp Rating at 240V: 50
KW Rating at 208V: 8.7
KW Rating at 240V: 11.6

Running a new #6 wire run is almost an impossibility (finished basement, etc).

I have been looking online and have found that there is an allowance for "Ranges" 8-12kW to be calculated as 8kW for demand. I don't however see that this demand allowance covers cooktops.

My question: is it feasable to hook the new cooktop to the current circuit, knowing that I may have to reset a breaker on occasion - or is this a real fire hazard even if I keep it on the 40 amp breaker.

FYI: electrician said no harm in hooking it up to current circuit since demand will unlikely ever be enough to trip circuit, and with the 40amp breaker I am safe.

Thanks for your help!
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Old 11-30-2010, 08:01 AM   #2
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Your electrician is correct. I've never seen a 40 Amp range circuit trip out from overload, even on units rated as high as yours.

Now IF you were to run all elements on "high" -- continuously -- that might be a problem. But in residential situations that is very unlikely to occur.

Life is uncertain -- eat dessert first!!
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Old 11-30-2010, 08:52 AM   #3
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I commend you for taking the effort to investigate this.

Around here, people just buy a range and plug it in, as if it's a table lamp. I haven't seen a non-functional combination yet.
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Old 11-30-2010, 10:33 AM   #4
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kbsparky - thank you very much for the reply. Having a second opinion on this really makes me feel better about it.

emolatur - thank you. I have been burned a bit lately by expert contractors, so I wanted to make sure and cover myself on this one.

#8 wire is approved for 50 amp circuits so long as it is a single run wire (not jacketed like romex). I feel this is because the romex jacket makes the wire combustable at a lower temp? The copper is capable of higher amps, just not the way it is housed (jacketed or non-jacketed).

So in that case would anyone feel that the romex #8 could be pushed to a 45amp breaker? I see that this is not legal according to the NEC, but it still is not the full jump to a 50 amp breaker, and the #8 copper can technically handle the amps (right?).

Now I assume this would void most homeowners insurance policies, but would anyone here do it in their own home? That is, switch out a 40 amp breaker with a 45 on Romex #8/3 to avoid having to run (say 75ft) #6 and busting out tons of drywall to do it.

I am just curious...
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Old 11-30-2010, 12:07 PM   #5
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No, I would leave the 40 amp breaker and the existing cable alone. I do have a couple questions though. Is there a receptacle existing for the old cook top? Or was it hardwired? Does the new range come with a cord and plug?

Here I found this for you.

334.80 Ampacity. The ampacity of Types NM, NMC, and
NMS cable shall be determined in accordance with 310.15.
The ampacity shall be in accordance with the 60C (140F)
conductor temperature rating.

This makes using a 45 amp circuit breaker a violation. The 40 amp breaker is as big as you can go with 8/3 NM.

Last edited by J. V.; 11-30-2010 at 12:19 PM.
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Old 11-30-2010, 12:45 PM   #6
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J.V. Thanks for your reply. The old cooktop is hardwired, the new cooktop is hard wired as well. Why do you ask?

Also, here is the breaker I was speaking of (45amp - my breakers are GE Thins):

I do know that the 45amp is bigger then allowed on 8/3 NM, but I had a electrician say if "it were my house, I might throw on a 50amp breaker (if I occasionally was throwing the breaker) 'cause the copper can handle the load, it's just the jacket that is killing the rating" but since it was not code he wouldn't go on the record saying that, and pointed out he would never do it to someone else's house. I guess he felt that NEC code is always going to be on the conservative side for universal safety. Going to a 50amp seemed too high to me, but what about a 45...?

I'm not an electrician, so I would wonder if the following analogy might help:

Driving down the highway the speed limit is 55 MPH. Many people may go 64 or 65 (still somewhat safe, but still breaking the law). But going 70 or 75 is starting to get a little dangerous. Back at 65MPH chances of your tires exploding or the engine exploding are still quite low, albeit higher then when you are going 55MPH.

55mph is a 40amp breaker
65mph is a 45
75mph is a 50

Is this analogy WAY off base? I feel that many electricians must have seen this before in the field - so were the wires hot?

Last edited by Addict; 11-30-2010 at 02:57 PM.
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Old 11-30-2010, 04:04 PM   #7
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Why do you want to take the chance? Leave the 40 amp breaker and sleep well. If occasionally you get a trip, you will know the system is protecting your family.
My electrical answers are based on 2014 NEC, you may have local amendments.

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Old 11-30-2010, 04:40 PM   #8
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Think about how this cook top will be used. There are 5 burners, now do you believe you will be running all 5 at the same time at a high power setting? What you should do is leave the 40 amp breaker in and then get a clamp on amp meter. Run three burners at high and see what the current draw is. The only issue is you will have to find a convenient place to access the wires.
I think you will find that the 40 amp breaker will be sufficient and you will be much safer.
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Old 11-30-2010, 04:53 PM   #9
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No more analogy's 8-3 wire 40 amp breaker that's it.

That electrician that told you he would put a 50 amp in do not listen to him anymore.

Sorry had to get it to you the Bill O Reilly way.
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Old 11-30-2010, 07:01 PM   #10
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As a licensed electrician I am required to wire an appliance to the NEC, applicable local codes and to the manufacturer's installation instructions. Will it still be under warranty if you don't wire per the installation instructions?
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Old 11-30-2010, 11:06 PM   #11
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Thank you everyone for your input!
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