40A or 50A Circuit

[gndrod]

1981

1981

I just reached up and grabbed a book and it states in 422-5 Exception 3 that branch ciruits supplying cooking appliances are premitted to be sized in accordance with Table 220-19 which is the same as Table 220.55 today. This is out of the 1984 cycle so I wouldn't think that it is something new

Mike,

You are inspiring. I also reached up and grabbed the 1981 cycle and to my surprise....[422-5] stated Exception 3 that branch circuits supplying household cooking appliances shall be permitted to be in accordance with Table 220-19 (220.55). At least there is a consistancy in the past.

The "in accordance" verbiage seems to qualify each particular statement as "shall be permitted" for DF calculations and "shall be sized" in appliance BC conductor installation as signified in [422.10]. So I guess I am asking everyone what their interpretation of why there is a somewhat conflicting two statement directions of the 2008 422.10? rbj

 

[Wire_nutz]

12.5 Kw - 12.0 KW = 0.5 KW
5% x 0.5 KW = 0.025 = 2.5%
2.5% x 8.0 KW = 0.2 KW
8.0 KW + 0.2 KW = 8.2 KW
8.2 KW = 8200 W
8200 W ? 240 V = 34.167 A

40 Amp Circuit

 

[gndrod]

12.5 Kw - 12.0 KW = 0.5 KW
5% x 0.5 KW = 0.025 = 2.5%
2.5% x 8.0 KW = 0.2 KW
8.0 KW + 0.2 KW = 8.2 KW
8.2 KW = 8200 W
8200 W ? 240 V = 34.167 A

40 Amp Circuit

wire nutz,
What is the difference from the Demand Factor calculation just given from T220.55 and the BC conductor sizing of 210.19 relative to Art.422.10. Thanks for the minimum calculation. rbj

 

[ivsenroute]

12.5 Kw - 12.0 KW = 0.5 KW
5% x 0.5 KW = 0.025 = 2.5%
2.5% x 8.0 KW = 0.2 KW
8.0 KW + 0.2 KW = 8.2 KW
8.2 KW = 8200 W
8200 W ? 240 V = 34.167 A

40 Amp Circuit

I agree and your math is exactly like mine.

I agree if the range is not continuous which I think most of us agree on.

40A min required by code
50A a good idea to install

 

[jwelectric]

Mike, You are inspiring.

Thank you

So I guess I am asking everyone what their interpretation of why there is a somewhat conflicting two statement directions of the 2008 422.10? rbj

Gndrod

I may be wrong with my assumption but I feel that you are under the impression that the first sentence of 422.10(A),
?(A) Individual Circuits. The rating of an individual branch circuit shall not be less than the marked rating of the appliance? should also apply to a cooking appliance.

There is a reason why the last sentence of 422.10(A) makes this statement,
Branch circuits and branch-circuit conductors for household ranges and cooking appliances shall be permitted to be in accordance with Table 220.55 and shall be sized in accordance with 210.19(A)(3).

Using the nameplate rating without any derating of a 12kw range and the voltage applied (240) this would call for a circuit of 50 amps but Table 220.55 lets us size this circuit at 40 amps see 210.19(A)(3). 8000/240 = 33.33 amps

Now the question is why this is allowed. I am a firm believer that seeing is believing so a simple experiment that any qualified electrician can perform is on their own cooking appliances.

Have someone turn on all the burners and oven while you take a reading with a clamp on meter. I bet you will be surprised with your findings after standing there for as little as two minutes.

When I turn on one of my large burners to high the burner will get red but if I turn it on to medium it will never get red, why?
Does the size of the burner change? NO
Does the resistance of the burner change? NO
Did I change the voltage by setting it to medium? NO
The controller controls the amount of current that the burner draws by letting the current flow intermediately instead of a constant draw at the full value of the burner.

Due to the way the current draw is on cooking appliances there is no need to have the branch circuit to conform to the nameplate rating of the range therefore the allowance for the derating. As one can see with a simple ammeter the current draw on a range is nowhere close to the rating of that cooking appliance at all times even with every thing turned on to high therefore the allowance to derate the size of the branch circuit.

 

[gndrod]

Edit Limit

Edit Limit

Mike,
I did give the wrong impression and the 10 minute edit limit cut me short to rephrase the lead-in statement. I am still interested in why the NEC made a somewhat double-edged revision to 422.10. The (A) Individual Circuits paragraph seems to imply differences in the two accordances, one "permitting" T 220.55 in circuit-load calculation Demand Factoring and the other [210.19(A)(3)] "shall be sized" conductor selection in the same sentence. Is this a dual statement for BC installation and load calculating guidelines?
There is an assumption in project plans (appliance legend not specified) that using Table 220.55 load derating determines the rough-in cabling conductor size for the final range-cooking unit loads to be installed. I believe that the above [422.10] revision is covering for the possible further interpretation of sizing an unknown range load yet to be determined.
In higher end residential, clients opt to install electrical ranges of commercial quality that exceed 14 kVa in some instances. I am not sure any sane EC would run 8 awg BC prior to final for a range hookup. There are times where applying NEC minimums can be flawed.
I was involved in such a situation some years back and the AHJ cited [210.19] for BC size enforcement but allowed T 220.55 for the project Service DF calculation sizing. The EC bit the bullet. (Amprobe readings were taken to show that a 14 kVa range fully energized can hold for some time on a 40A OCPD, 8 awg BC. Termination excess heating occurred as an issue for long term degradation.) rbj

 

[guschash]

Table 220.55 Note 1

Around 12.5 up to 13

13kw - 12kw = 1kw
increase column c by 5%
8kw x 5% = 400
8000 + 400 = 8400
8400/240 = 35
35 x125% =43.75
50A
If range is going to operate 3hrs or more I say 50A

 

[jwelectric]

Mike, I was involved in such a situation some years back and the AHJ cited [210.19] for BC size enforcement but allowed T 220.55 for the project Service DF calculation sizing. The EC bit the bullet. (Amprobe readings were taken to show that a 14 kVa range fully energized can hold for some time on a 40A OCPD, 8 awg BC. Termination excess heating occurred as an issue for long term degradation.) rbj

So what you are saying is a 16kw range that comes with a 50 amp cord can not be plugged into a 50 amp receptacle?

Wonder why they would waste the time to ship it with a 50 amp cord?

I would install this 16kw range on a #8 and a 40 amp breaker to a 50 amp receptacle and never worry one second about the installation.
There is a reason why this is allowed and if it were unsafe it wouldn't be allowed.

 

[LarryFine]

If range is going to operate 3hrs or more I say 50A

It won't, as far as NEC definitions are concerned. The elements cycle to maintain temperature.

 

[acrwc10]

So what you are saying is a 16kw range that comes with a 50 amp cord can not be plugged into a 50 amp receptacle?

Wonder why they would waste the time to ship it with a 50 amp cord?

I would install this 16kw range on a #8 and a 40 amp breaker to a 50 amp receptacle and never worry one second about the installation.
There is a reason why this is allowed and if it were unsafe it wouldn't be allowed.

Would you do this even if the installation instructions from the manufacturer required a higher ampere circuit ?
I ask this because I have a job right now with a "Thermador" double oven and the requirement is for a 60amp circuit, and like you said there is no way it will ever hit that load for any amount of time, if ever.But that is what they call for and this is common in the installation instructions that the circuit required exceeds table 255.
I will look today to see what the KW rating is on the oven.
By the way thank you for chiming in on this thread, even though you said you weren't going to because it seemed "so simple". There are a lot of people that don't read this section the way you do ( many inspectors included ) and good arguments for it ( as you have included ) help all who read this thread to look more closely at the articles and notes, you need to remember many people don't have the years of experience you do.:smile:

 

[jwelectric]

Would you do this even if the installation instructions from the manufacturer required a higher ampere circuit ?
I ask this because I have a job right now with a "Thermador" double oven and the requirement is for a 60amp circuit, and like you said there is no way it will ever hit that load for any amount of time, if ever.But that is what they call for and this is common in the installation instructions that the circuit required exceeds table 255.
I will look today to see what the KW rating is on the oven.
By the way thank you for chiming in on this thread, even though you said you weren't going to because it seemed "so simple". There are a lot of people that don't read this section the way you do ( many inspectors included ) and good arguments for it ( as you have included ) help all who read this thread to look more closely at the articles and notes, you need to remember many people don't have the years of experience you do.:smile:

If the manufactures instructions call for a larger circuit then by all means install the larger circuit.

In 42 years of doing electrical installations I have never seen a range that calls for more than a 50 amp circuit. I have seen double ovens that called for a 40 amp circuit but most are 30 amps.

Unless the double oven calls for a individual circuit I would install the oven you mention above by Note 4 of Table 220.55 and 210.19(A)(3) Exception 1.

If the appliances or the information for the appliances are not present at the time the rough-in then the NEC is the only guideline the installer and the code official have to work with. Therefore unless the two (cook top and oven) added together are more than 22kw then a 50 amp circuit is what I would install. If it is 16kw or less then a 40 amp circuit.

Now if when the appliances are delivered they call for individual circuits someone is coming off the hip with some pictures of Ben or they can change their appliances which ever the general and homeowner decides.

In spec houses and apartments I always install a 40 amp circuit as this will cover most ranges. In custom houses I always ask about the appliances, heat and air conditioner unless that information is provided with the specs. Should there be a conflict at finial then someone is coming off with more money of live with what they got.

 

[jwelectric]

Would you do this even if the installation instructions from the manufacturer required a higher ampere circuit ?

I ask this because I have a job right now with a "Thermador" double oven and the requirement is for a 60amp circuit, and like you said there is no way it will ever hit that load for any amount of time, if ever.But that is what they call for and this is common in the installation instructions that the circuit required exceeds table 255.
I will look today to see what the KW rating is on the oven.
By the way thank you for chiming in on this thread, even though you said you weren't going to because it seemed "so simple". There are a lot of people that don't read this section the way you do ( many inspectors included ) and good arguments for it ( as you have included ) help all who read this thread to look more closely at the articles and notes, you need to remember many people don't have the years of experience you do.

If the manufactures instructions call for a larger circuit then by all means install the larger circuit.

In 42 years of doing electrical installations I have never seen a range that calls for more than a 50 amp circuit. I have seen double ovens that called for a 40 amp circuit but most are 30 amps.

Unless the double oven calls for a individual circuit I would install the oven you mention above by Note 4 of Table 220.55 and 210.19(A)(3) Exception 1.

If the appliances or the information for the appliances are not present at the time the rough-in then the NEC is the only guideline the installer and the code official have to work with. Therefore unless the two (cook top and oven) added together are more than 22kw then a 50 amp circuit is what I would install. If it is 16kw or less then a 40 amp circuit.

Now if when the appliances are delivered they call for individual circuits someone is coming off the hip with some pictures of Ben or they can change their appliances which ever the general and homeowner decides.

In spec houses and apartments I always install a 40 amp circuit as this will cover most ranges. In custom houses I always ask about the appliances, heat and air conditioner unless that information is provided with the specs. Should there be a conflict at finial then someone is coming off with more money of live with what they got.

After making this post I got to thinking about something.

Can anyone say that they have seen a range that had a cord that was larger than 50 amps?

Can a single receptacle have a rating less than the rating of the branch circuit supplying it?

This question excludes cook tops and built in ovens. Can anyone say that they have seen a residential free standing range that was required to be hard wired?

 

[LarryFine]

Can a single receptacle have a rating less than the rating of the branch circuit supplying it?

I say no, because the receptacle's rating is supposed to indicate the capacity of the circuit.

 

[raider1]

I say no, because the receptacle's rating is supposed to indicate the capacity of the circuit.

I agree, take a look at 210.21(B)(1).

Chris

 

[M. D.]

I have never seen a residential range requiring a 60 amp circuit

 

[acrwc10]

After making this post I got to thinking about something.

Can anyone say that they have seen a range that had a cord that was larger than 50 amps?[/SIZE]

Can a single receptacle have a rating less than the rating of the branch circuit supplying it?

This question excludes cook tops and built in ovens. Can anyone say that they have seen a residential free standing range that was required to be hard wired?

No to all three questions. I have hard wired ranges but they where not required to be hard wired.It was more an issue of no room for a receptacle and cord ( flex 90 takes up less space )

 

[Greg1707]

EC Magazine

EC Magazine

There is an article in Electrical Contractor Magazine 12.08 issue on this very subject. I was of the opinion that 220.55 was used only for calculating the total load of a service, however; the article in ECM page 79 uses 220.55 for sizing the branch circuit conductors.

 

[CopperTone]

40 amp circuit.


- As per 220.55, using the Table 220.55, column C.
- 12.5kW is a "major fraction thereof" (note 1)

the demand load is 8kW

8000W x 1.05 = 8400W/240V = 35Amps

This is the correct way. Pretty cut and dry

 

[acrwc10]

This is the correct way. Pretty cut and dry

What if the range was 14 KW, I'm not sure you math would work.:-?

 

[ronmath]

Ivsenroute has the calculations correct. Look at the definition of a continuous load under article 100. An electric range in a residence would not be a continuous load. According to the load then we could use a 35A/2P breaker, except that article 210.19(3) requires a minimum of 40 amps for ranges over 8-3/4KW or more. So the answer would be a 40 amp circuit minimum.