Electrical Range Calculation

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tacomafc

Senior Member
Please help me make sure this calculation is correct for a 12.9 KW range.

12.9 KW-12.0KW= .9 KW

.9KW x 5%=.o45% or 100.045%

100.045% x 8kw= 8.0036kw

8.0036kw rounds down to 8KW or 8000 W/240V = 33.3 amps

wire size # 8 thhn awg.
breaker 40amp

Thank you
 

bcorbin

Senior Member
I'm confused where you are getting these rounding schemes. Ranges are resistive loads, which typically means their rating is going to be their fully-loaded amperage. This would be 53.75 A, as Shockin said. Even if you use a 70A breaker (53.75*1.25 rounded up, but consult your range manufacturer's specs for requirements), you're gonna need more than #8's.
 

jwelectric

Senior Member
Location
North Carolina
  • Over 12 kW through 27 kW ranges all of same rating. For ranges individually rated more than 12 kW but not more than 27 kW, the maximum demand in Column C shall be increased 5 percent for each additional kilowatt of rating or major fraction thereof by which the rating of individual ranges exceeds 12 kW.
12.9 KW-12.0KW= .9 KW or 1
1 X 5% = 5%
8 X 105% = 8.4
8400/ 240 = 35

210.19(A) (3) Household Ranges and Cooking Appliances. Branch-circuit conductors supplying household ranges, wall-mounted ovens, counter-mounted cooking units, and other household cooking appliances shall have an ampacity not less than the rating of the branch circuit and not less than the maximum load to be served. For ranges of 8? kW or more rating, the minimum branch-circuit rating shall be 40 amperes.
 

bcorbin

Senior Member
Once again, the code fails us. If you breaker this circuit at 40 amps, it's going to nuisance trip a lot.
 

bcorbin

Senior Member
Well, I guess I'm going to have to take my college-boy self back to the books and figure out why not. I love it when I find out everything I've been taught is not true.
 

roger

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bcorbin said:
Once again, the code fails us. If you breaker this circuit at 40 amps, it's going to nuisance trip a lot.

Bcorbin, If you were to put a recording meter on this range for a year you would probably never see it get close to 40 amps even including the heavy Thanksgiving and Christmas cooking days. :)

Roger
 

iwire

Moderator
Staff member
Location
Massachusetts
bcorbin said:
Well, I guess I'm going to have to take my college-boy self back to the books and figure out why not. I love it when I find out everything I've been taught is not true.

As Roger pointed out the rating and what it really uses are different issues.

UL, the manufacturers and the NEC are all on the same page (most times;)).

Sure I agree with you that if the unit actually used 53 amps for more than a few minutes the breaker would trip.

However it is very unlikely that will ever happen.

Maybe I will put an amp clamp on my range and see what I can max it out at. :)
 

roger

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Shockin, I shouldn't be answering for Mike, but I will anyways, :D Hope you don't mind Mike. ;)

These words are the answer to you question " the maximum demand in Column C" The maximum demand for one range is 8 kw.

Roger
 

jwelectric

Senior Member
Location
North Carolina
shockin said:
Jw - why wouldn't it be 12kw x 105%? I don't see why you get to go back down to 8 kw at that step.

Over 12 kW through 27 kW ranges all of same rating. For ranges individually rated more than 12 kW but not more than 27 kW,

This range falls in to this category

the maximum demand in Column C

I found the ?8kw? from Column C

shall be increased 5 percent for each additional kilowatt of rating or major fraction thereof by which the rating of individual ranges exceeds 12 kW.

.9 is a major fraction as outlined in 220.5(B)
 

jwelectric

Senior Member
Location
North Carolina
roger said:
Shockin, I shouldn't be answering for Mike, but I will anyways, :D Hope you don't mind Mike. ;)

These words are the answer to you question " the maximum demand in Column C" The maximum demand for one range is 8 kw.

Roger

Thank you Roger I was a little slow in gathering my info

Edited to add

didn't see page two Imust be getting old
 

bcorbin

Senior Member
I guess I'm just of the mentality "the best value to the customer." A 40A breaker is going to trip at 32A. So....in order to save the customer an extra 50 dollars in materials, let's hamstring his 12.9kW range to only being able to put out 7.7kW (five hand-held hair dryers)? If you're going to "el cheapo" him on the circuit, tell him to save his money and buy a cheaper, smaller range.
 

jwelectric

Senior Member
Location
North Carolina
bcorbin said:
I guess I'm just of the mentality "the best value to the customer." A 40A breaker is going to trip at 32A. So....in order to save the customer an extra 50 dollars in materials, let's hamstring his 12.9kW range to only being able to put out 7.7kW (five hand-held hair dryers)? If you're going to "el cheapo" him on the circuit, tell him to save his money and buy a cheaper, smaller range.

What size circuit is recommended by the manufacture of the range?
This can be found in the owner?s manual.

I have been researching this for the past couple of months by looking at every range I come in contact with.
I have yet to find one that requires more than a 50 amp circuit with most of them saying min. 40 max. 50 amp.
I am hoping to find one that requires a circuit of more than 50 amperes before I die.

Now based on your post I think we all should send a letter to these manufactures and express our opinion that the circuit is not large enough.
 

bcorbin

Senior Member
Well....if the manufacturer is advertising his product as a 12.9kW range when, following his own recommendations, will only deliver 7.7kW, maybe you're right.
 

haskindm

Senior Member
Location
Maryland
bcorbin,
Why would a 40 amp breaker trip at 32 amps? Do not be confused about continuous loads being limited to 80% of a circuit breakers ampacity. A range is NOT a continuous load. A circuit breaker will carry its rated amperage at its rated ambient temperature indefinitely. In fact it will carry an amperage well above its rated amperage for a long time. That is why we need an effective ground fault return path; so that in the event of a fault the circuit breaker will see an amperage of many times its rating and trip quickly. It would be VERY difficult to trip a 40-amp breaker from the load you could generate with a range rated 12.9KW. Perhaps possible, but not likely in normal use.
 

roger

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Location
Fl
Occupation
Retired Electrician
Bcorbin, why do you think any 40 amps breaker will trip at 32 amps.

We are only allowed to load a breaker to 80% for a continuous load, but a breaker will not trip at 80%, it probably wouldn't trip a little over 100%.

As far as the continuous load is concerned, as long as it is interupted every 179 minutes or less, we don't have to concern ourselfs with it.

Roger
 

roger

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Ooops, I appologize Haskindm, I was typing while you were posting.

Roger
 
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