Breaker size for oven

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I have a 50-amp breaker on a circuit previously used for a double oven. The new oven draws 3400 watts on 4000 watts at 240 volts, depending on whether you believe a plate on the oven or the manual. I think that's either 14.2 amps16.7 amps.
The question is whether I need to change the breaker, and, if so, whether I need to also change the wire in the wall and ceiling, which is 6-gauge aluminum. One person said a 50-amp breaker is too big because the oven internal wiring could burn out before tripping the breaker. I understand that logic, but if it's a legitimate concern then why wouldn't this call for a 20-amp breaker? Nobody, I think, would use a 20-amp breaker on an oven circuit -- always 30 or more.
What would you do, and why?
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Are the wattage ratings for all 4 burners on high, and the oven in preheat mode? Or...other?
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imho:
Check your 'cut sheet' for breaker requirements. Tyically the breaker is designed for protecting the wires, but some manufactures want a specific size breaker for their products.
later,
tom @ www.NoCostAds.com
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watts=current(amps) x voltage current = watts / voltage so......... current = 4000 / 240volts or 16.77777 amps
so you would need (two) 20 amp breakers at the panel .......one per 120volt line.
As long as you are going from a larger breaker to a smaller one, no worry is needed for the wiring part. If you were increasing the amps.....then the wiring would have to be a concern. A minimum of 12 gauge should be sufficient in your case at 4000 watts.
Here is a link that will help you..........
http://muextension.missouri.edu/explore/agguides/agengin/g01409.htm
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No, and no.
First, should be 30 amps. An electric stove meets the Code definition of a "continuous load", and thus the circuit is limited to 80% of the breaker rating. 80% of 20 amps is 16.0 amps. A 17-amp continous load requires the next size up breaker, which is 30 amps.
Second, it must not be two separate breakers, but rather one double-pole breaker.
--
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Doug Miller (alphageek at milmac dot com)
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On Sat, 04 Nov 2006 13:59:50 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

Any new breaker for a 240V circuit needs to be double-pole, but is it important enough to replace older ones that aren't double-pole?
--
51 days until the winter solstice celebration

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Yes -- it's a Code violation, and a safety hazard, to use two separate 120V breakers for a 240V circuit unless the handles are tied together to as to produce a *single* disconnect for *both* hot conductors.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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Two clarifications:
1. The suggestion that two electricians gave me is to use a 20-amp or 30-amp double-pole breaker, so there's no need to discuss one vs. two breakers here.
2. This is a wall oven only on a dedicated circuit. There is a separate circuit for a cooktop elsewhere in the kitchen.
A rant:
The manufacturer, Frigidaire/Electrolux, is almost useless. Like a lot of big companies, it has a customer-service organization apparently designed to block consumers from getting in touch with any knowledgeable person. The manual and the customer service people just say conform to your local codes, ask your own electrician, etc., when presented with a problem such as how to connect the oven's small 16-gauge copper wire to 6-gauge aluminum in the wall, for which nobody makes a connector.
A conclusion:
As for the circuit rating, I quote from the multiple-model manual:
"The fuse size must not exceed the circuit rating of the appliance specified on the nameplate."
There is no "circuit rating" on the nameplate. There is only the wattage, which is 3.4 kw at 240 volts and a similar number for 208 volts, which I guess is for Canada.
Quoting further from the manual:
"The single wall oven can consume up to 4000W at 240 Vac; use a circuit breaker of 30 Amp with wire gauge #8 AWG."
This figure of 4000 watts disagrees with the 3.4 kw on the nameplate. So that leaves us with either 14.2 or 16.7 amps.
Thanks for the information about the 80 percent rule. I had not heard of that. Does that mean that, even on a circuit for a single appliance, the breaker size should be 1/.8 (1.25) times the maximum expected load on the circuit?
If I am interpreting that correctly, then a 20-amp double-pole breaker would handle a load of 14.2 amps multiplied by 1.25, but a 16.7-amp load multiplied by 1.25 would call for a 20.9-amp breaker, so I'd go up to 30 amps. In light of the ambiguity of the manufacturer's information, 30 amps seems best.
Does that make sense? Any other thoughts?
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The manufacturer isn't being ambiguous. Voltages vary and wattages will vary with the voltage differences. The manufacturer says to use a 30 amp breaker with #8 copper. What don't you understand?

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RBM (remove this) wrote:

If the manual says 4000 watts and the plate on the oven says 3.4 kilowatts, that looks ambiguous to me.
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This is often done with a small breaker box.

No, we're 240V just like you. 208V is when it's powered off two hots of a 3 phase circuit. The legs are 120V referenced to neutral, but 208V apart. You see this in industrial/commercial, especially "warehouse->office" conversions, staff areas in industrial buildings etc. Quite rare in straight residential, but sometimes...

Exactly.
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Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
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On Sat, 04 Nov 2006 20:09:08 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

Having the breakers tied together, also prevents the dumb questions like, I installed both breakers, but nothing happens. Each hot gives me 120v to ground, but then to each other, I get 0. WTF?
<rest head in my hand, shaking>
:p
later,
tom @ www.IRantAndRave.com
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avid_hiker wrote:

only for straight resistance devices
now most heating elements change in resistance as they change in tempature, so the wattage listed might not for max, but for power output while at temp.
also, the stovetop burners *might* be 120V (2 burners for each side of the 240)
my advice, find the nameplate, contact the manufacturer, and find out what wiring and breaker to use. they know the right answer, as telling the wrong one sets them up for a lawsuit
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I would size the wire and breaker per the manufacturers specs.
The breaker is there for over current protection on the WIRE. Not your equipment. It is there for short circuit protection as well.
If you have over sized wire on a breaker you are putting the circuit as a SYSTEM out of whack.
Most typical breakers operate on heating at the terminations of the breaker. And of course amp draw. Both of these are all enginneered in the breaker.
A #6 wont heat up as much on a 45 amp load that a #10 will.

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Tazz wrote:

Tazz: A #6 *wire* won't heat up as much as a #10 *wire* will, given the same load. But both will heat up the internal element of a 50 amp circuit breaker the same amount. In fact, the #6 circuit will have less voltage drop. With more voltage available at the oven, if something internally shorts out, more current will flow, tripping the breaker more quickly. You don't have to consider house wiring as a system with the breaker like that. We are not making a resonant RLC circuit here. Hook up a 15A breaker to a #14 circuit and another 15A breaker to a 500 MCM circuit, and both will be protected at 15A for house- wiring purposes, though the 500 MCM will be grotesquely overdoing things and certainly difficult to wrap around those device screws. :)
Cordially yours: G P.
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Point taken, And I stand corrected.
Typically the OCP protects only the conductors. Is it ok to oversize the conductors on any application?
I have heard of oversizing grounds and neutrals on computer and lighting loads for harmonic issues. But have never heard using larger conductors on the line voltatge.. Of course the OP has this as an existing situation and not a new install. I suppose this is why the code addresses minimums and not maximums. makes sense.
I would agree that getting a 500kcmil around a screw on an outlet will be somewhat hard. But dont you know someone will try to engineer it at some point and time. LOL
respectfully
Tazz.

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Yes. And no... ;-)
It's reasonably common to upsize the conductors a notch or two for various reasons - eg: reduction of resistive voltage drop on long circuits.
However, it's expensive to do, and in many cases you can run into situations where the wire size exceeds the permissible range on the devices you connect it to. You're going to flunk an inspection with 0000 wire on a 15A outlet for example.
The inspector may ask, for example, "why the heck are you using 10ga on a 15A outlet?" You'd better have a good answer, or the inspector may flunk you for workmanship.
"The circuit is so long that 10ga limits my voltage drop to 3V" is a good answer. "I had a chunk laying around" is probably a bad one.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
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BobH wrote:

BH:
Who?
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If the unit draws 4kw, the NEC requires you to use minimum #10 copper, with 30 amp breaker. The #6al is fine, but I'd reduce the breaker size

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You don't need to change the wire, as long as it's larger than the minimu.
If you do need to change the breaker, and assume that the 16.7A is correct, by the 80% rule you'd have to use a 30A dual breaker. [NOT two individual breakers]
But, before you do that. Do you have a cooktop too?
By NEC and CEC rules, a wall oven and cooktop are permitted to be on the same breaker, with ampacity determined by the total of the two rated current requirements. [In fact, at least with the CEC, under certain restrictions, the wire to the oven only has to be large enough for the oven draw, not the full breaker current. Eg: you'd might run #8 or #6 on a 40 or 50A circuit to a splitter box, which splits to two 10ga cables to the oven and cooktop.]
In your case, it's already #6Al, but is the 50A circuit shared with a cooktop? If so, you have to factor that in too in your breaker size calculation.
I'm a little suspicious of a 50A circuit ONLY feeding an oven, but the risks (burnout of oven wiring itself) are fairly low.
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Chris Lewis, Una confibula non set est
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