For a residential range that is rated at 9.5kW at 208 single phase, can I go to 220.19 and use 8kW for the demand? The manufacturer recommends 40 amp breaker. At 9kW I'm looking at 43.3A which would be more than the breaker rating. Even at 8kW I'm looking at 38.5A. Will the 40A breaker be ok?
Residential Electric Range
- Thread starter new_ee
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- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Residential Electric Range
Do not confuse the demand load that applies to the service load calculation with the sizing of the branch circuit conductors and their overcurrent protection device. You have to size the branch circuit for the actual load. You don't get to use the tabulated demand factors here. The branch circuit has to be able to handle whatever current the load will draw. But from the viewpoint of the service load calculation, there is a good chance that the stove will not be at full power at the same time as the dishwasher, clothes washer, heater, and (biggest load of all) the hair dryers used by the women of the house.
But back to the branch circuit. First of all, does the manufacturer allow use of this range on a 208 volt system? Presuming that answer is "yes," is that rating of 9.5kW based on 240 volts? If so, the range will consume far less power at 208. The ratio of power is the square of the ratio of voltages, so at 208 volts it would draw about 7135 watts. That equates to about 34 amps at 208 volts. So a 40 amp breaker should be fine.
It's usually safe to go with the manufacturer's recommended sizes, unless you know something unusual about the particular installation.
Do not confuse the demand load that applies to the service load calculation with the sizing of the branch circuit conductors and their overcurrent protection device. You have to size the branch circuit for the actual load. You don't get to use the tabulated demand factors here. The branch circuit has to be able to handle whatever current the load will draw. But from the viewpoint of the service load calculation, there is a good chance that the stove will not be at full power at the same time as the dishwasher, clothes washer, heater, and (biggest load of all) the hair dryers used by the women of the house.
But back to the branch circuit. First of all, does the manufacturer allow use of this range on a 208 volt system? Presuming that answer is "yes," is that rating of 9.5kW based on 240 volts? If so, the range will consume far less power at 208. The ratio of power is the square of the ratio of voltages, so at 208 volts it would draw about 7135 watts. That equates to about 34 amps at 208 volts. So a 40 amp breaker should be fine.
It's usually safe to go with the manufacturer's recommended sizes, unless you know something unusual about the particular installation.
Re: Residential Electric Range
the range is rated 12.5kW @ 240 and 9.5kW @ 208. Where do I look to size the breaker? Beacause 9.5kW at 208 is 43.3A which wouldn't really work on the manufacturer's recommended 40A breaker. Thanks for pointing out that the demand table can only be used for service calculations. It made me re-read it and see that that is in fact the case.
the range is rated 12.5kW @ 240 and 9.5kW @ 208. Where do I look to size the breaker? Beacause 9.5kW at 208 is 43.3A which wouldn't really work on the manufacturer's recommended 40A breaker. Thanks for pointing out that the demand table can only be used for service calculations. It made me re-read it and see that that is in fact the case.
bphgravity
Senior Member
- Location
- Florida
Re: Residential Electric Range
Actually, you can use Table 220.55 for the branch circuit load for one range. See note 4 to the table. So you only need to figure 8kW for that range which is generally served by a 40A circuit.
Actually, you can use Table 220.55 for the branch circuit load for one range. See note 4 to the table. So you only need to figure 8kW for that range which is generally served by a 40A circuit.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Residential Electric Range
My hat's off (and my head is cold) to Byran.
Didn't someone once say that it doesn't say what you think it says?
Now that I have looked at that Note 4, I am confused. It's worded in a bizarre way. For one range, you can use the table. But there is only one number in that entire table of dozens of numbers that would apply in that circumstance (top row, right hand column). Note 4 might just as well have said, "use 8 kW for one range."
But what it does say is that "it shall be permissible . . . ." So the code does allow you to use the 8kW value and a 40 amp breaker. I wouldn't. I'd go with a 50 amp breaker, and size the conductor accordingly. But as has been said by many (myself included), that is a design choice, not a code requirement.
My hat's off (and my head is cold) to Byran.
Didn't someone once say that it doesn't say what you think it says? Now that I have looked at that Note 4, I am confused.
It's worded in a bizarre way. For one range, you can use the table. But there is only one number in that entire table of dozens of numbers that would apply in that circumstance (top row, right hand column). Note 4 might just as well have said, "use 8 kW for one range."But what it does say is that "it shall be permissible . . . ." So the code does allow you to use the 8kW value and a 40 amp breaker. I wouldn't. I'd go with a 50 amp breaker, and size the conductor accordingly. But as has been said by many (myself included), that is a design choice, not a code requirement.
jwelectric
Senior Member
- Location
- North Carolina
Re: Residential Electric Range
Let?s also take a close look at 210.19(A)(3)
Let?s also take a close look at 210.19(A)(3)
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Residential Electric Range
The question here is whether that "maximum load to be served" is 8 kW or 9.5 kW. I'm still not sure I know.
bphgravity
Senior Member
- Location
- Florida
Re: Residential Electric Range
In my opinion, the maximum load to be served is the load as determined by Article 220. I follow this line of reasoning based on the wording in 215.2(A)(1) and 230.42(A). Unfortunately, 210.19 makes no mention of 220 yet Article 220 is where branch circuit loads are calculated.
In my opinion, the maximum load to be served is the load as determined by Article 220. I follow this line of reasoning based on the wording in 215.2(A)(1) and 230.42(A). Unfortunately, 210.19 makes no mention of 220 yet Article 220 is where branch circuit loads are calculated.
john m. caloggero
Senior Member
Re: Residential Electric Range
All electric ranges I have wired were listed by a recognized testing laboratory, such as UL. The instructions accompanying a listed product are required to be followed in accordance with NEC section 110.3(B). In addition, Article 220 does apply to load calculations for branch-circuits. A 40 ampere overcurrent device is permitted by the Code. The size of the branch circuit conductors must have an ampacity of not less than 40 amperes when supplied by a 40 ampere overcurrent device. I recommend installing a 50 ampere overcurrent device and No. 8, cu, with insulation rated at least 75 degrees C, terminating in terminals rated at 75 degrees C.
All electric ranges I have wired were listed by a recognized testing laboratory, such as UL. The instructions accompanying a listed product are required to be followed in accordance with NEC section 110.3(B). In addition, Article 220 does apply to load calculations for branch-circuits. A 40 ampere overcurrent device is permitted by the Code. The size of the branch circuit conductors must have an ampacity of not less than 40 amperes when supplied by a 40 ampere overcurrent device. I recommend installing a 50 ampere overcurrent device and No. 8, cu, with insulation rated at least 75 degrees C, terminating in terminals rated at 75 degrees C.
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