40A or 50A Circuit

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40A or 50A Circuit

  • 40A circuit

    Votes: 38 54.3%
  • 50A circuit

    Votes: 32 45.7%

  • Total voters
    70
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ivsenroute

Senior Member
Location
Florida
You make the call.

Single Family Residence with an electric range rating of 12.5kW @ 240vac.

Would you install a 40A circuit and receptacle or a 50A circuit and receptacle?

How did you arrive at your decision.

NEC 2005 applies along with Table 220.55

Let's see how different we are.
 

benaround

Senior Member
Location
Arizona
ivsenroute,

I'll give it a shot.

12.5kw = 8kw + (8kw * .5%)

circuit = 8040kw

8040kw/ 240 = 33.5amps

33.5a = 40a circuit

Am I close ?
 

ivsenroute

Senior Member
Location
Florida
The question is: Is a range considered a continuous load?

If it is then 125% of 33.5A is 41.9A

Does this affect what size circuit you will install?
 

peter

Senior Member
Location
San Diego
Table 220-5 or whatever it is, is the most ornery and awkward section in the Code. [725 is the stupidest Article.]
I just divided 12,500 by 240 volts and got about 50 amps, so 50 Amps it is.
I realize that there is some derating involved, but how much does the price change? If you wire it for 50, you've got everything covered.
This brings up the entire flaw in the Section: at the time you are designing/estimating, you do not know what kind of stoves the customer will be using. Maybe it's a spec house and, when it is sold, the purchaser will move his own stove in.
~Peter
 

ivsenroute

Senior Member
Location
Florida
My math is a little different.

Note one states that the max demand in column C shall be increased by 5% for each kW above 12. There is only a half of a kW so I only added 2.5% to make it easier.

8kW x 2.5%= .2kW

8.2kW/240= 34.2A

If not a continuous load then 40A for a 34.2A load is acceptable.

If it is a continuous load then a 40A circuit would be required.
 

ivsenroute

Senior Member
Location
Florida
Table 220-5 or whatever it is, is the most ornery and awkward section in the Code. [725 is the stupidest Article.]
I just divided 12,500 by 240 volts and got about 50 amps, so 50 Amps it is.
I realize that there is some derating involved, but how much does the price change? If you wire it for 50, you've got everything covered.
This brings up the entire flaw in the Section: at the time you are designing/estimating, you do not know what kind of stoves the customer will be using. Maybe it's a spec house and, when it is sold, the purchaser will move his own stove in.
~Peter

I like your thinking but if you do it your way 12,500/240 is 52A so you would be installing a 60A circuit?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
not to mention leaving the oven door open to warm the house..............
(I work a back woods area)
 

acrwc10

Master Code Professional
Location
CA
Occupation
Building inspector
I just connected one today it came with a 50 amp cord on it so it got a 50 amp circuit :smile: didn't know the KW at rough in so I went with the standard "it requires a 50 amp circuit" that I always get when I ask what the KW is.
 

iwire

Moderator
Staff member
Location
Massachusetts
If not a continuous load then 40A for a 34.2A load is acceptable.

If it is a continuous load then a 40A circuit would be required.

There is no way I would consider a range a continuous load based on the NEC definition found in '100'.

I really do not understand this part of 220 and given the range of answers I guess I am not the only one.
 

iwire

Moderator
Staff member
Location
Massachusetts
most every thanksgiving my oven runs for well over 3 hrs. how can it not be a continuous load ?

Read the definition of continuous load, it is not enough for the range to be on for more then 3 hours, the maximum load must be maintained for more then 3 hours.

There is no way that all four burners and the oven are on 100% for 3 hours.
 
There is no way I would consider a range a continuous load based on the NEC definition found in '100'.

I really do not understand this part of 220 and given the range of answers I guess I am not the only one.




I concur with that.


When I am teaching calculations in class, I make the comment that 5 engineers providing calculations for a job will come up with 5 different answers for the same question. :grin:
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
most every thanksgiving my oven runs for well over 3 hrs. how can it not be a continuous load ?

No, it still is very unlikely that it did not cycle on and off many times in an hour.

My answer here depends on the wire size. If rated for 50 then i put in 50 breaker. Will it ever hit that long enough to matter ? Your seldom at full load on most appliances. I did back off my 15 kw heat strip on main part of house to 10 kw, simply no need for it here and save room for intertainment room 800 sq feet with heat pump. In 10 years have never ever tripped the 200 amp main. Curious what electric bill and gas/oil total up north. Mine total electric 2600 feet plus hot tub 24/7 at 102 and 500 sq feet screened room for pool table and tub .plus 300 more sq feet on saturday nights for my cabin. Bill $250 to $350 depending on month.
 

hardworkingstiff

Senior Member
Location
Wilmington, NC
not to mention leaving the oven door open to warm the house..............
(I work a back woods area)

In 1978, I actually did that. Out of work, no money for oil. I knew the PoCo would not cut power in the winter, so we had one 120-volt plug in space heater (1000 watt) and the oven to heat our 2-bedroom duplex. Those were tough times. My daughter was 2. It was pretty bad back then.
 

paul

Senior Member
Location
Snohomish, WA
In 1978, I actually did that. Out of work, no money for oil. I knew the PoCo would not cut power in the winter, so we had one 120-volt plug in space heater (1000 watt) and the oven to heat our 2-bedroom duplex. Those were tough times. My daughter was 2. It was pretty bad back then.

I remember dad turning on the burners to help heat up the house when I was a young lad. But yet we were not allowed to use the dishwasher because it cost too much money. I guess when you have slave labor (kids) you can do that. ;)
 
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