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undersized circuit breaker?


Jaykline
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I did an inspection for a friend this past weekend and included the following comment in my report:

"The 240 volt circuit breaker labeled 'Oven' in the service panel is a 15-amp circuit breaker that controls the circuit fed by what appears to be #6AWG conductors. The oven is a JennAir (Maytag) Model # JJW953ODDP, Serial # 21335016JG with the following rating:

120/240 volt = 3.6 KW

120/208 volt = 2.7 KW

The manufacturer's recomended overcurrent protection for this oven is:

0-4.8 KW = 20-amp"

Other than the fact that the circuit was not installed according to the manufacturer's recommendation, how significant is/are the problem(s)related to the undersized breaker? Does the use of #6 conductors mitigate any potential problems - or does it compound them?

Since the condition was not done to manufacturer's specs, I wrote it up, but I'd like to understand the "why" a little better, so I can put it into perspective for the client (and myself).

Any feedback will be appreciated. Thanks.

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"120/240 volt = 3.6 KW" which does equal 15 amps for the 240 volts. However, nuisance tripping from initial surge or all-on use might be a problem and I'd recommend changing to a 20-amp breaker. Nothing actually un-safe about the 15 amp tho.

Also nothing wrong with oversized wires for the circuit (or any circuit come to that). Fairly common to use the existing 50-amp range circuit wiring rather than run new cable. The only question is...how did they get the #6 into a 15 amp breaker? I believe most 15/20 amp breaker lugs are rated/sized for no more than #8, meaning you would have to pigtail or otherwise splice to the #6s.

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Hi,

You didn't say whether the AWG was copper or aluminum. The cheat sheet that I have had for the past 10 years says that on a 240-volt circuit a #6 AL cable will pull up to 6720 watts with a 35 amp breaker without problems and a #6 CU cable can pull up to 9600 watts with a 50 amp breaker without problems, so the cables, as you've already stated, aren't an issue.

What's happened is that someone has essentially put a governor on that range that will trip and cut off fuel long before the engine reaches maximum revs - if you can understand the analogy.

The comment is waaay too techno though. You're client needs to understand the what and why. I had to read that several times to absorb it and I've been doing this 10 years! Oh, yeah, I forgot - I am kind of dense. Sorry. Anyway, my point is that, since you knew that the wires to the range were not going to be a problem, you could have said:

The breaker in the service panel used for the electric range is smaller than allowed. This range is designed to draw up to 4,800 watts, which will normally cause a 15-amp breaker to trip and cut power to the range. Since the range isn't tripping this 15-amp breaker, I have to conclude that it's defective. I recommend having an electrician replace it now with a 20-amp breaker, which is the correct size to use for this range.

That's what I would have said.

ONE TEAM - ONE FIGHT!!!

Mike

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This range is designed to draw up to 4,800 watts, which will normally cause a 15-amp breaker to trip and cut power to the range. Since the range isn't tripping this 15-amp breaker, I have to conclude that it's defective.

Mike...I think you misread that. The original post states that they recommend a 20-amp breaker for any oven 0 through 4.8 KW but this particular one is rated at 3.6KW (15-amps at 240 volts). I don't think the oven is "defective" because it's not tripping a 15-amp breaker. Still should have the recommended 20-amp breaker tho.

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He is saying that the 15 amp breaker is not defective. The unit is rated at 3.6 kw which pulls 15 amps. So this unit is pulling 15 amps on a fifteen amp breaker. All is well. The wrong part is simply that the manufacturer recommends 20 amps.

I think you are confusing the 0-4.8 kw=20-amp part as implying this unit is a 4.8 kw unit. It is 3.6 amps @ 15 amps draw.

Buster

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The oven is a JennAir (Maytag) Model # JJW953ODDP, Serial # 21335016JG with the following rating:

120/240 volt = 3.6 KW

120/208 volt = 2.7 KW

The manufacturer's recomended overcurrent protection for this oven is:

0-4.8 KW = 20-amp"

Spending way too much time on this but...

The way I'm reading that is that this particular oven has a 3.6 KW rating at 240 volts. That equates to 15 amps. They then sensibly reccomend a 20 amp breaker for any oven up to 4.8 KW. The point I'm getting at is that a 15-amp breaker not tripping would not mean it or the 15-amp max oven was defective.

To be honest, if they aren't already experiencing nuisance tripping with the 15-amp breaker, then there probably ain't nuttin' wrong in a purely practical sense and changing out to a 20-amp has no effect (function or safety). But, as the manufacturer reccomends a 20-amp breaker it should have one.

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Originally posted by Jaykline

I did an inspection for a friend this past weekend and included the following comment in my report:

"The 240 volt circuit breaker labeled 'Oven' in the service panel is a 15-amp circuit breaker that controls the circuit fed by what appears to be #6AWG conductors. The oven is a JennAir (Maytag) Model # JJW953ODDP, Serial # 21335016JG with the following rating:

120/240 volt = 3.6 KW

120/208 volt = 2.7 KW

The manufacturer's recomended overcurrent protection for this oven is:

0-4.8 KW = 20-amp"

Other than the fact that the circuit was not installed according to the manufacturer's recommendation, how significant is/are the problem(s)related to the undersized breaker?

Probably not very significant. Sizing a circuit breaker to match 100% of a permanently installed load always makes me uncomfortable, but it's permitted by the NEC unless the load is "continuous." An oven is not continuous. I'd tell them to increase the size of the breaker to comply with the tag on the oven. But practically speaking, the worst that'll happen might be nuisance tripping of the breaker and that's pretty unlikely.

Does the use of #6 conductors mitigate any potential problems - or does it compound them?

It's better than using smaller wire. It doesn't hurt anything.

Richard - some 15-amp breakers, such as Cutler Hammer, will accept a #6 wire.

Since the condition was not done to manufacturer's specs, I wrote it up, but I'd like to understand the "why" a little better, so I can put it into perspective for the client (and myself).

Any feedback will be appreciated. Thanks.

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Originally posted by Jaykline

I did an inspection for a friend this past weekend and included the following comment in my report:

"The 240 volt circuit breaker labeled 'Oven' in the service panel is a 15-amp circuit breaker that controls the circuit fed by what appears to be #6AWG conductors. The oven is a JennAir (Maytag) Model # JJW953ODDP, Serial # 21335016JG with the following rating:

120/240 volt = 3.6 KW

120/208 volt = 2.7 KW

The manufacturer's recomended overcurrent protection for this oven is:

0-4.8 KW = 20-amp"

Other than the fact that the circuit was not installed according to the manufacturer's recommendation, how significant is/are the problem(s)related to the undersized breaker?

Probably not very significant. Sizing a circuit breaker to match 100% of a permanently installed load always makes me uncomfortable, but it's permitted by the NEC unless the load is "continuous." An oven is not continuous. I'd tell them to increase the size of the breaker to comply with the tag on the oven. But, practically speaking, the worst that'll happen might be nuisance tripping of the breaker and that's pretty unlikely.

Does the use of #6 conductors mitigate any potential problems - or does it compound them?

It's better than using smaller wire. It doesn't hurt anything.

Richard - some 15-amp breakers, such as Cutler Hammer, will accept a #6 wire.

Since the condition was not done to manufacturer's specs, I wrote it up, but I'd like to understand the "why" a little better, so I can put it into perspective for the client (and myself).

Any feedback will be appreciated. Thanks.

Your recommendation was fine, if overly technical. The "why" is just to comply with the manufacturer's safety margin.

Mike - breakers aren't designed to trip immediately at their rated amperage unless there's a direct short or fault. There's a time/trip curve for each breaker. It could take a long time for a breaker to trip when overloaded by a percentage of its load. So a 30-amp breaker that didn't trip when an oven pulled 4,800 watts wouldn't necessarily be defective. I'd just take some time. You'd have to consult the breaker’s time/trip curve chart to find out how long.

- Jim Katen, Oregon

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