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10-07-2013, 12:58 PM   #1
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## How are stove amperages calculated?

Hello all,

How do stove manufacturers calculate the amperage ratings for their stoves?

I ask because our stove calls for - and has been on for 30 years - a 50 amp circuit.

The problem is that I did a calculation by adding up the wattage of all the oven and surface elements and that indicates it should be on a 70 amp circuit.

I don't understand. Can someone enlighten me?

(2) 2600w surface elements = 5200w
(2) 1500w surface elements = 3000w
One large oven at 5800w
One small oven at 3000w

A total of 17000w at 240v is 70.1amps when I do the math.

Jim

10-07-2013, 01:12 PM   #2
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It is based on the fact that all the elements are not likely to be on FULL at the same time.

 The Following User Says Thank You to joed For This Useful Post: Know A Little (10-07-2013)
 10-07-2013, 01:41 PM #3 Member   Join Date: Apr 2010 Location: central wisconsin Posts: 779 Rewards Points: 500 nec allows demand factors for ranges and other cooking appliances, for just the reason joed mentions above. check 220.55
 10-07-2013, 08:50 PM #4 Member   Join Date: Jun 2012 Location: Kentucky Posts: 69 Rewards Points: 83 And commercial ranges would fall under another section of the NEC? I went poking around and a Garland commercial electric range with nearly the same kW rating as our old Kenmore calls for the full breaker capacity. The reasoning would be that in a commercial environment, it would be more likely for all the heaters to be on full at the same time? Thanks, Jim
10-07-2013, 09:01 PM   #5
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Quote:
 Originally Posted by simanco And commercial ranges would fall under another section of the NEC? I went poking around and a Garland commercial electric range with nearly the same kW rating as our old Kenmore calls for the full breaker capacity. The reasoning would be that in a commercial environment, it would be more likely for all the heaters to be on full at the same time? Thanks, Jim
And operate for a longer period of time.

10-08-2013, 05:33 AM   #6
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Quote:
 Originally Posted by simanco And commercial ranges would fall under another section of the NEC? I went poking around and a Garland commercial electric range with nearly the same kW rating as our old Kenmore calls for the full breaker capacity. The reasoning would be that in a commercial environment, it would be more likely for all the heaters to be on full at the same time? Thanks, Jim
Quote:
 Originally Posted by Know A Little And operate for a longer period of time.
Not likely unless you want to burn all the food to a crisp.

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10-08-2013, 05:33 AM   #7
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Quote:
 Originally Posted by simanco Hello all, How do stove manufacturers calculate the amperage ratings for their stoves? I ask because our stove calls for - and has been on for 30 years - a 50 amp circuit. The problem is that I did a calculation by adding up the wattage of all the oven and surface elements and that indicates it should be on a 70 amp circuit. I don't understand. Can someone enlighten me? (2) 2600w surface elements = 5200w (2) 1500w surface elements = 3000w One large oven at 5800w One small oven at 3000w A total of 17000w at 240v is 70.1amps when I do the math. Jim
there is a tag on the oven ... with the wattage ..usually in the front ..
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10-08-2013, 05:58 AM   #8
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Quote:
 Originally Posted by simanco A total of 17000w at 240v is 70.1amps when I do the math. Can someone enlighten me? Jim
This is sort of on the line if you were to add all the breakers up in your electrical panel.

Most likely to be much higher than your main breaker rating. Mine is 500

10-08-2013, 07:28 AM   #9
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Quote:
 Originally Posted by kbsparky Not likely unless you want to burn all the food to a crisp.

My point was commercial stoves operate for long periods of time, while in a residential application it is a cook and done

10-08-2013, 07:33 AM   #10
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Quote:
 Originally Posted by Know A Little My point was commercial stoves operate for long periods of time, while in a residential application it is a cook and done
I own a restaurant and our equipment is turned on at 10:30 am-1:30 am 7 days a week and the meter just goes "cha ching cha ching"

 The Following User Says Thank You to wirenut1110 For This Useful Post: Know A Little (10-08-2013)
 10-08-2013, 08:17 AM #11 Member   Join Date: Oct 2011 Posts: 505 Rewards Points: 718 even if the oven was at 100% load, a 50 amp breaker at 70 amp will take few minutes before tripping. Pretty sure the oven has some type of limiting current also, it can deactivate some heater. If you put your your surface element at high they will stop after few minutes because they will overheat, so there a not a continuous load, same thing for the oven.
10-08-2013, 09:17 AM   #12
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Quote:
 Originally Posted by carmusic even if the oven was at 100% load, a 50 amp breaker at 70 amp will take few minutes before tripping. Pretty sure the oven has some type of limiting current also, it can deactivate some heater. If you put your your surface element at high they will stop after few minutes because they will overheat, so there a not a continuous load, same thing for the oven.
A 50 amp molded case circuit breaker will handle 70 amps a 40% overload for a LONG TIME, may not trip for hours, depending on adjacent circuit breakers and the ambient at the panel. A typical molded case residential style circuit breaker will handle 300% overload for 35-80 seconds, on average not verifying the Time Current Curve for any particular circuit breaker based strictly on experience.

10-08-2013, 09:37 AM   #13
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Quote:
 Originally Posted by Know A Little A 50 amp molded case circuit breaker will handle 70 amps a 40% overload for a LONG TIME, may not trip for hours, depending on adjacent circuit breakers and the ambient at the panel. A typical molded case residential style circuit breaker will handle 300% overload for 35-80 seconds, on average not verifying the Time Current Curve for any particular circuit breaker based strictly on experience.
yep, breakers can carry overloads for a damn long time. it is a misconception that a, say, 20 amp breaker will trip right at 20 amps. it could very well carry 22 amps indefinitely and never trip.

of course, one should never knowingly overload a circuit breaker. it is bad practice and prohibited by code.

10-08-2013, 11:05 AM   #14
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Quote:
 Originally Posted by simanco Hello all, How do stove manufacturers calculate the amperage ratings for their stoves? I ask because our stove calls for - and has been on for 30 years - a 50 amp circuit. The problem is that I did a calculation by adding up the wattage of all the oven and surface elements and that indicates it should be on a 70 amp circuit. I don't understand. Can someone enlighten me? (2) 2600w surface elements = 5200w (2) 1500w surface elements = 3000w One large oven at 5800w One small oven at 3000w A total of 17000w at 240v is 70.1amps when I do the math. Jim
Quote:
 Originally Posted by joed It is based on the fact that all the elements are not likely to be on FULL at the same time.
Taking this a step further.
Imagine the size of the service for an apartment building if they used the 50 amp load for every apartment or condo.
In this example, the NEC is assuming all of the ranges will never be on at the same time.
Its called derating. Derating allows the engineer or contractor to be able to install in a practical manner while installing for safety.

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10-08-2013, 11:34 AM   #15
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and the derates for large buildings are insane. the oven/range load for a 41 unit apartment is 25 kw plus 3/4 kw for each additional range or about 56 kw TOTAL, even though there may be more than 330 kw of connected load. the assumption is that no more than 10 or so units will be using the equipment at the same time. there is no scientific method to determining these derates, it is all based on past experience.

but yeah, if everyone in the building turned their ovens on at the same time, likely some breakers will start popping!

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