Commercial Sized Electric Range for Single Family Residence IRC/NEC

[jar546]

Educational (for all of us):

You receive a set of prints for a new addition which will pave the way for a large kitchen expansion on an existing single family residence. The family is big on cooking and plans on using a commercial sized electric range that has a rating of 21kW. It will be the only range in the house on its own circuit.

What size circuit (OCPD & wire type/size) is required for this installation?

 

[jwelectric]

50 amp breaker and using NM-B #6

 

[jar546]

50 amp breaker and using NM-B #6

I don't understand how you got that

 

[raider1]

I don't understand how you got that

Take a look at Note #4 to Table 220.55. This note allows you to size the branch circuit for a single range in accordance with Table 220.55.

If you look at Column C for ranges over 8 3/4 KW and Note #1 you will see that for ranges over 12kw and not exceeding 27 kw you increase the demand in Column C by 5% for each additional kilowatt of the range exceeding 12 kw.

So we have a range that is 21 kw. We start with 8 kw for a single range from Column C and increase it by 45%. You get 45% because you have 9 kw over the base 12 kw. So you multiply 8 kw by 45% and you get 3.6 kw so you round up to 4 kw. You add 4 kw and 8 kw and get 12 kw. You divide 12 kw by 240 volts and you get 50 amps. You look at Table 310.15 on the 60 degree column and find that #6 copper has an ampacity of 55 amps.

Chris

 

[north star]

+ + +

"What size circuit (OCPD & wire type/size) is required for this installation?"

What the manufacturer of that appliance requires on the Installation Guidelines !Surely, ...the homeowners will want the new appliance installed according the

manufacturer' Installation Guidelines and to local codes, so that they won't

void any warranties.

+ + +

 

[jar546]

Take a look at Note #4 to Table 220.55. This note allows you to size the branch circuit for a single range in accordance with Table 220.55.If you look at Column C for ranges over 8 3/4 KW and Note #1 you will see that for ranges over 12kw and not exceeding 27 kw you increase the demand in Column C by 5% for each additional kilowatt of the range exceeding 12 kw.

So we have a range that is 21 kw. We start with 8 kw for a single range from Column C and increase it by 45%. You get 45% because you have 9 kw over the base 12 kw. So you multiply 8 kw by 45% and you get 3.6 kw so you round up to 4 kw. You add 4 kw and 8 kw and get 12 kw. You divide 12 kw by 240 volts and you get 50 amps. You look at Table 310.15 on the 60 degree column and find that #6 copper has an ampacity of 55 amps.

Chris

Thank you for that great explanation Chris. I hope that a lot of people pay attention to your post.

 

[jar546]

+ + +What the manufacturer of that appliance requires on the Installation Guidelines !

Surely, ...the homeowners will want the new appliance installed according the

manufacturer' Installation Guidelines and to local codes.

+ + +

That was not the point of this exercise and many times the instructions are to comply with local codes so all inspectors and electricians should know how to do this. I love questions like this because I know that they are helpful to many.

 

[north star]

% % %

"That was not the point of this exercise and many times the instructions are to comply with local codes so all inspectors and electricians should know how to do this. I love questions like this because I know that they are helpful to many."

That was why I posted my comment Jeff !......Not all electricians knowhow to perform the calculations required, hence, ...always read & follow

the instructions of the manufacturer.......If an electrician cannot read

the instructions, they may not be able to perform the math either !

As we all know, ...the manufacturer' requirements supercede / trump /

overrule the codes !

FWIW, ...I agree that this is a good question and exercise.

Keep `em coming !



& & &

 

[Dennis]

Ranges throw everyone for a loop. I find it very interesting that any range greater than 8 3/4 kw and 16kw can be wired to a 40 amp circuit. Go figure.. but it's compliant. Smallest size for a range greater than 8 3/4 KW is 40 amps-- 210.19(A)(3).

16Kw following the same logic that Chris stated 8 kw plus 5% for each kw over 12KW. That would be 4 *5%= 20%. 8kw from column C So you have 8 kw *20%= 1.6. 8 kw + 1.6 kw = 9.6kw

9600/240= 40 amps

 

[ICE]

% % %

As we all know, ...the manufacturer' requirements supercede / trump /

overrule the codes !



& & &

That's not always true. I have encountered manufacturers installation instructions that contain blatant code violations.

 

[jwelectric]

What that is written on paper that is packed with the equipment is not what the NEC is addressing with 110.3(B).

Read what is written in this section of the code.

(B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.

The UL White Book is a good place to start.

 

[Dennis]

Mike I was told b a UL guy that the instructions were part of the listing.

 

[jwelectric]

Mike I was told b a UL guy that the instructions were part of the listing.

True the installation instructions that are included in the listing and labeling process are the instructions referred to by 110.3(B) and can be found in the White Book or Guide published by UL.

I have seen many manuals that would use the word “recommended” which is not an instruction but is instead a recommendation.

My dishwasher has a nameplate that says 10 amps but in the manual it says, “Recommended 20 amp circuit.” It is installed on a 15 amp circuit which is code compliant.

422.10 Branch-Circuit Rating.

This section specifies the ratings of branch circuits capable of carrying appliance current without overheating under the conditions specified.

(A) Individual Circuits. The rating of an individual branch circuit shall not be less than the marked rating of the appliance or the marked rating of an appliance having combined loads as provided in 422.62.

422.62 Appliances Consisting of Motors and Other Loads.

(A) Nameplate Horsepower Markings. Where a motor-operated appliance nameplate includes a horsepower rating, that rating shall not be less than the horsepower rating on the motor nameplate. Where an appliance consists of multiple motors, or one or more motors and other loads, the nameplate value shall not be less than the equivalent horsepower of the combined loads, calculated in accordance with 430.110©(1).

(B) Additional Nameplate Markings. Appliances, other than those factory-equipped with cords and attachment plugs and with nameplates in compliance with 422.60, shall be marked in accordance with 422.62(B)(1) or (B)(2).

(1) Marking. In addition to the marking required in 422.60, the marking on an appliance consisting of a motor with other load(s) or motors with or without other load(s) shall specify the minimum supply circuit conductor ampacity and the maximum rating of the circuit overcurrent protective device. This requirement shall not apply to an appliance with a nameplate in compliance with 422.60 where both the minimum supply circuit conductor ampacity and maximum rating of the circuit overcurrent protective device are not more than 15 amperes.

 

[Dennis]

True the installation instructions that are included in the listing and labeling process are the instructions referred to by 110.3(B) and can be found in the White Book or Guide published by UL. I have seen many manuals that would use the word “recommended” which is not an instruction but is instead a recommendation.

My dishwasher has a nameplate that says 10 amps but in the manual it says, “Recommended 20 amp circuit.” It is installed on a 15 amp circuit which is code compliant.

No argument there from me..

 

[jar546]

I too will concur with that logic