Amperage for an electric cooktop?

[dexlargo]

My cooktop keeps blowing its screw-in fuses. I think I've got the problem figured out, but I thought I'd check to see if anyone here can see a problem I'm missing...

My cooktop appears to have replaced an older model (replaced by previous home owner), and the fuse box for the cooktop has spots for 4 fuses, but when I open it up, I see that only 2 are actually connected to the appliance.

It appears that the current cooktop uses a 240V 3 - wire connection (two hots, no neutral, and a ground), and that's what's coming from the panel. The fusebox has labels indicating that the two fuses (each of the hot lines are fused) that actually connect to the cooktop should be 15 Amps. That's what was in the box, and that's what keeps blowing.

I think that the sticker is wrong - that it must indicate the amperage for the old cooktop for the small burners or something.

The current cooktop has a rated peak load of 6.1kW, so with 240V service, this would indicate that it needs ~25.5 Amps to supply that load, hence the blown fuses.

So I think that I should be okay to just replace these 15 Amp fuses with 30 Amp fuses and carry on - and remove the stupid misleading sticker.

I'm no electrician and I'm afraid I know just enough to be dangerous. Does anyone know anything about this kind of electrical? Is there something that I'm missing? Because the circuit is supplied by ganged 40 amp breakers, should I be able to assume that the wire is good for 30 Amps?

[masoncgy]

The vast majority of cooktops on the market require at least a 30 amp circuit, with many calling for 40 amp. Hell, some induction cooktops need a 50 amp circuit now.

I would assume that the draw of the new cooktop is too much for the current circuit.

I can't advise any further though... haha. I'm no electrician! ;)

[Shibumi]

We had an Electrolux induction stove installed last year and the store (Sears) recommended a 50 amp circuit. Our electrician felt more comfortable with a 60 amp circuit.

Our friends have an induction cooktop with a 30 amp circuit and they find that they can't run all four burners simultaneously. One of the burners will not power up.

[rx7_turbo2]

The wire that feeds the cooktop, what size is it? The circuit breaker that feeds the cooktop what size is it?

[dexlargo]

Originally posted by Shibumi
We had an Electrolux induction stove installed last year and the store (Sears) recommended a 50 amp circuit. Our electrician felt more comfortable with a 60 amp circuit. Mine is not an induction cooktop, it's a ceramic one with the radiant elements underneath. Its peak draw is listed as 6.1 kW. - It's a 30" cooktop, so not one of the huge ones.


Originally posted by rx7_turbo2
The wire that feeds the cooktop, what size is it? The circuit breaker that feeds the cooktop what size is it? The wire gauge is either 10 or 12 - I would have to check tonight to be sure.

Each hot is connected to a 40 amp breaker.

The circuit length from breaker box to the appliance is not more than 50 feet (probably less - I'd have to measure).

For the issue of wire gauge, shouldn't I be able to assume that the electrician that ran the original wire would have put in an appropriate gauge of wire for the length of the run and the breaker installed?

[rx7_turbo2]

Don't assume anything lol!!! #12Awg is rated to 20a, and #10 to 30a. They are fed by 2 seperate 40a breakers? Or did I read that wrong? If the breaker size is 40a then the wire size should be #8awg and the breaker should be a 2 pole, single pull unit, meaning the breaker will disconnect both phases in the event either one is tripped. If this is not the case then we need to start there.

The internal wiring of the cooktop will also be rated for a certain load, that's why without some sort of documentation I'd be leary about just jamming a bigger fuse in there.

[dexlargo]

Yes, the two 40 amp breakers are connected together - the standard way that you see for a dryer circuit or a stove circuit, etc, so that if one breaker tripped, the other would trip as well.

I didn't check the gauge of wire last night. Too busy, but I'll look tonight.

Using wiring size calculators on the internet (e.g. here (http://www.gorhamschaffler.com/wire_size_calculator.html)), I get that for 40 amps at 50 feet at 240V, I need 10 gauge wire, if 40 feet then 12 gauge should be fine.

Shouldn't I be able to trust the wire size calculators?

Another issue - what is standard here, 240V or 208V? Is there a way to check what the supply would be, because that does appear to make a difference.

[rx7_turbo2]

Electrical standards are different everywhere. Canadian Electrical Code, the ONLY code that matters where we live, and the ONLY code your insurance company will care about in the event of an electrical fire when it decides to deny your claim states the maximum allowable ampacity for #12 AWG copper conductors is 20A, and 30a for #10AWG. Meaning in order for your installation to meet the standards set out by our country's governing body the wire size MUST be #8AWG.

In our country both 240v and 208v are standard or "nominal" voltages. And also very common. For residential applications you will be dealing with 240V. 208v is a commercial voltage for the most part and there is no need (or desire on my part) to explain where and why 208v exists.

Again even if the wiring is #8 I'd still be leary about swapping out fuses on the cook top until I was CERTAIN the internal wiring of the unit could handle it. But that's just me. I wouldn't EVER suggest it but hey it aint my house, you could always jam some bigger ones in there and "see what happens" I guess lol.

[dexlargo]

Thanks, I think I see now.

I checked the wire and it's 12/2, so it's 12 gauge, which might be sufficient from a voltage drop perspective but is not allowable as per current code, so I should pull a new 8 AWG wire.

As for the internal wiring of the appliance: I double checked the plate on the device and it actually lists 8.1 kW for 240V, 6.1 kW is for 208V. Are those the numbers that you would use to calculate what the internal wiring is rated to handle?

If it helps, here is a link to the installation manual for my cooktop: http://manuals.frigidaire.com/prodinfo_pdf/Lassomption/318201410.pdf

Unfortunately, the install manual is one that was created for a variety of cooktops, so it doesn't give specific electrical requirement information for each one.

Thanks for the help!

[rx7_turbo2]

Alright. So 8.1kw/240v gives us 33.75a. Now according to the manual the unit must be fused at no greater than that load rating, and since we can't by 33.75a fuses 30a should suffice. That's what you thought all along so cool!

However we do need to address the circuit that feeds the cooktop as you mentioned. You are going to need to pull a set of #8awg conductors to your cooktop, and the current 40a circuit breaker will now be properly protecting the wire. That should solve your issues, and get you back up to code!