Range Wire Sizing

[jeff43222]

I just got hired to wire up a new electric range, and when I looked at the nameplate and the installation instructions, I wound up unsure as to what size circuit I should install.

The nameplate rating for 120/240V said 14.4 kW. My calculator says that the amperage for such wattage would be 57.5 - 60A (depending on whether you use 240V or 250V). Either way, my thinking was that this installation would call for a 60A circuit.

But the instructions that came with the range called for a minimum 40A, maximum 50A circuit. I don't see how 14.4 kW is possible on a 40A circuit. Sure, I could install for 40A, but if the homeowner cranks the thing up and does a lot of cooking, the breaker would trip long before get gets the 14.4 kW he paid for. Usually when I wire up ranges, the nameplate wattage and the circuit size in the instructions agree with each other.

Or am I missing something here?

 

[bdarnell]

Can you get on the manufacturer's website and confirm the kW rating ? That's one honkin' big range. I've got a brand new Jenn-Air top of the line and it's only rated at 11.4 kW.

 

[Cavie]

I see a lot of 13.5 smooth top ranges every day. I allow 50 amp

 

[RUWired]

Jeff, Two possible explainations could be article 422.10(A)

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
Or
Branch circuits for household cooking appliances shall be permitted to be in accordance with Table 220.55.In table 220.55,Note 1
1. Over 12 kW through 27 kW ranges all of same rating. For ranges individually rated more than 12 kW but not more than 27 kW, the maximum demand in Column C shall be increased 5 percent for each additional kilowatt of rating or major fraction thereof by which the rating of individual ranges exceeds 12 kW.
With a 14.4kw range,You will increase the demand of 8 kw 15%.(9200)/240=38.33 (40)

That might be how they came up with the 40a.
The conductors would be sized on the rating (#8 (40a)min-#6(50a) max).

(3) Household Ranges and Cooking Appliances Branch-circuit conductors supplying household ranges, wall-mounted ovens, counter-mounted cooking units, and other household cooking appliances shall have an ampacity not less than the rating of the branch circuit and not less than the maximum load to be served. For ranges of 8 3/ 4 kW or more rating, the minimum branch-circuit rating shall be 40 amperes.
Rick

 

[jeff43222]

This is one of those smooth top ranges. I was pretty surprised to see such a high kW rating, too.

It's all starting to come back to me. This stuff was on the exam. I haven't had occasion to look at Table 220.19 since then, though, as most people I deal with tend to cook with gas.

Your explanation makes sense. Thanks, Rick.

 

[jwelectric]

Re: Range Wire Sizing

But the instructions that came with the range called for a minimum 40A, maximum 50A circuit. I don't see how 14.4 kW is possible on a 40A circuit.

210.19(A)(3) Household Ranges and Cooking Appliances Branch-circuit conductors supplying household ranges, wall-mounted ovens, counter-mounted cooking units, and other household cooking appliances shall have an ampacity not less than the rating of the branch circuit and not less than the maximum load to be served. For ranges of 8 3/ 4 kW or more rating, the minimum branch-circuit rating shall be 40 amperes.

 

[dlhoule]

I find the actual loads on ranges seldom come close to name plate. I am glad this came up though. About 10 years ago, I replaced a 60A breaker for range with a 30A. This ocurred early on Thanksgiving. The 60 was bad and the poor lady wanted to prepare dinner. All I had of the proper style was a 30. I told her that "if you have any trouble before I get back to call & I'll be there in 2 - 3 hours. Well, I forgot and she never called. Now I am going to have to go put a 60A back in.
Thanks!

 

[iwire]

Re: Range Wire Sizing

the minimum branch-circuit rating shall be 40 amperes.

Yes Mike the minimum not the maximum. :lol:

I take that to mean that a 8.75 KW range (36 amps @ 240) will have a minimum branch circuit rating of 40 amps.

However a 14 KW range (58 amps @ 240) will need a larger than the minimum 40 amp branch circuit.

It is inconceivable to me that the NEC would allow a range with a tag that says 58 amps to be suppled with a 40 amp circuit.

Not to say it would not work.

 

[jwelectric]

Bob reread that section:

For ranges of 8? kW or more rating, the minimum branch-circuit rating shall be 40 amperes.

The way I read it is that I could install a 27kw range on a 40 amp circuit

 

[iwire]

Bob reread that section:

For ranges of 8? kW or more rating, the minimum branch-circuit rating shall be 40 amperes.

The way I read it is that I could install a 27kw range on a 40 amp circuit

Yeah I reread it and I still think your mistaken.

If it meant what you say it does IMO the language would be more like this.

For ranges of 8? kW or more rating, the maximum branch-circuit rating required shall be 40 amperes

 

[jwelectric]

Bob reread that section:

For ranges of 8? kW or more rating, the minimum branch-circuit rating shall be 40 amperes.

The way I read it is that I could install a 27kw range on a 40 amp circuit

Yeah I reread it and I still think your mistaken.

If it meant what you say it does IMO the language would be more like this.

For ranges of 8? kW or more rating, the maximum branch-circuit rating required shall be 40 amperes

No my friend I am only quoting the section of code as it is written and it is written as I have posted.

210.19(A) (3) Household Ranges and Cooking Appliances. Branch-circuit conductors supplying household ranges, wall-mounted ovens, counter-mounted cooking units, and other household cooking appliances shall have an ampacity not less than the rating of the branch circuit and not less than the maximum load to be served. For ranges of 8? kW or more rating, the minimum branch-circuit rating shall be 40 amperes.

It also states in section 210.55 that any range rated in excess of 1? kW shall be permitted to be calculated in accordance with Table 220.55.

220.55 Electric Ranges and Other Cooking Appliances ? Dwelling Unit(s).
The load for household electric ranges, wall-mounted ovens, counter-mounted cooking units, and other household cooking appliances individually rated in excess of 1? kW shall be permitted to be calculated in accordance with Table 220.55. Kilovolt-amperes (kVA) shall be considered equivalent to kilowatts (kW) for loads calculated under this section.

I am sorry if you do not like this but this is something that you will need to address to panel 2 as I have no control over this section of the NEC.

 

[iwire]

Mike you can post the same words from here to eternity.

You can post in red, blue or plaid.

The minimum circuit required is not the maximum circuit required.

I don't know how you could turn this around so badly. :lol:

It's strange how you choose to ignore what comes first.

Branch-circuit conductors supplying household ranges, wall-mounted ovens, counter-mounted cooking units, and other household cooking appliances shall have an ampacity not less than the rating of the branch circuit and not less than the maximum load to be served

But hey I don't do residential so maybe I have my head up my....

Do you have any outside source you can cite for this view? :?:

 

[jes25]

Iv'e never seen a 60A range cord. Do they make ssuch a thing?

 

[jwelectric]

Why would I need an outside source when I have the words that are printed in the NEC itself?

I choose to use red type instead of the quote code due to the fact that I have a hard time reading the quotes. It was not to stress the point.

Do the math and tell me what would be the demand would be for a 22kw range. What would the circuit require if there was no demand?
As you can see there is a lot of give in the circuit for ranges.

Should I decide to install a 40 amp circuit would not the overcurrent device trip before any danger of an overload on the conductors?

 

[iwire]

Why would I need an outside source when I have the words that are printed in the NEC itself?

I asked because as many times as read this;

For ranges of 8? kW or more rating, the minimum branch-circuit rating shall be 40 amperes.

I can not for the life me comprehend why you see it as this;

For ranges of 8? kW or more rating, the maximum branch-circuit rating required shall be 40 amperes.

Like I said I admit I do not use this section of the code in my day to day work. However I have always assumed I had a good handle on the different definitions of maximum and minimum.

Main Entry: min?i?mum
Pronunciation: 'mi-n&-m&m
Function: noun
Inflected Form(s): plural min?i?ma /-n&-m&/; or -i?mums
Etymology: Latin, neuter of minimus smallest; akin to Latin minor smaller -- more at MINOR
1 : the least quantity assignable, admissible, or possible
2 : the least of a set of numbers; specifically : the smallest value assumed by a continuous function defined on a closed interval
3 a : the lowest degree or amount of variation (as of temperature) reached or recorded b : the lowest speed allowed on a highway
- minimum adjective

Main Entry: minimum
Part of Speech: adjective
Definition: least
Synonyms: least possible, littlest, lowest, merest, minimal, slightest, smallest, tiniest
Antonyms: maximum, most
Source: Roget's New Millennium? Thesaurus, First Edition (v 1.1.1)
Copyright ? 2006 by Lexico Publishing Group, LLC. All rights reserved.

Mike I am not being a wise @8% I am truly lost as to you thoughts on this section.

Maybe an outside source that you could point to would show me the error of my thoughts.

 

[George Stolz]

With a 14.4kw range,You will increase the demand of 8 kw 15%.(9200)/240=38.33 (40)

Rick, I believe you increase by 20%.

Counting on my hand (as juvenile as I might be for doing so), I get 12.5 (5%), 13.0 (10%), 13.5 (15%), 14.0 (20%). The .4 is a minor fraction that gets dropped.

Same difference in this case, I ended up with 40amps minimum branch circuit as well.

The way I read it is that I could install a 27kw range on a 40 amp circuit.

Mike, that's not true. In no case shall it be less than 40 amps, despite using any prescribed demand ratings.

27kW is 15 kW over 12kW.
15kW x 10% per kW = 150%.
8kW x 250% = 20kW
20kW x 1000 = 20000W
20000W / 240V = 83.3 amps

You would need a 90 amp branch circuit for this range.
You would not need 112A conductors on a 125A circuit for it, though, because you are allowed to demand the load on the branch circuit.

No way can you simply install a 40 amp branch circuit for the range and call it good.

 

[jwelectric]

Bob this is as easy as falling off a log.
Open your book in the 2005 it is on page 49 and the left column at the bottom. Read the last sentence of that section which states that the MINIMUM branch circuit is 40 amperes.
As the NEC is a MINIMUM standard it is saying that this is the smallest circuit that is allowed for a range 8 ? KW and larger.

A circuit for a 6kw oven would require what size circuit?
Unless the nameplate of installation instructions mandated something different I would install #12 conductors and a 20 amp breaker.

George you are way off base with your calculation above.

We are permitted to use table 220.55 to calculate a range as follows (using your 27kw range)

27 exceeds 12 by 15
Increase the demand in column (C) 5% for each kw that 27 exceeds 12
15 x 5 = 75%
Column (C) gives 8kw for one range
8 x 175% = 14kw
14kw divided by 240 volts = 58 amps

Now if we use the first sentence of 210.19(A)(3) in the context that some are saying then this circuit would require a 60 amp circuit.
Ever seen a 60 amp range cord?
What is the largest range cord you ever saw?

 

[George Stolz]

George you are way off base with your calculation above.

Darn tootin' I was. Sorry about that. I knew something was off in my head, I was cursing the whole time I was typing, 'cause I couldn't come up with it. Too little coffee at that point. Figured it was better just to get it out there than not figure out my mental snafu at all!

That's why I was so darned explicit about how I was getting my number. I knew something was shorted in my brain. :lol:

We are permitted to use table 220.55 to calculate a range as follows (using your 27kw range)

Which is in contrast to doing it the normal way, using the entire load instead of demanding it. If we weren't permitted to demand it, then we'd have to use the full load.

Ever seen a 60 amp range cord?
What is the largest range cord you ever saw?

Ever seen a hard-wired cooking appliance, Mike?

What is the point of going to the trouble of all that math, if you're always allowed to just install a 40A circuit and forget about it? You're not making any sense, think about it. What's the point of allowing us to calculate a branch circuit load according to a demand table, if we can overlook the results and just put in a minimum?

The whole code's a minimum, Mike.

 

[jwelectric]

Well George the way I figure it is that Table 220.55 goes all the way up to 61 ranges and over. They wanted to give us a way to install all of these ranges on one feeder instead of running a 40 amp circuit to each one of them.

Besides I didn?t write the NEC but I sure like quoting it.

 

[iwire]

Bob this is as easy as falling off a log.
Open your book in the 2005 it is on page 49 and the left column at the bottom. Read the last sentence of that section which states that the MINIMUM branch circuit is 40 amperes.

I have seen the section.

I have read the section.

Stop talking down to me and realize I am not a first year student.

I still can not see how you figure the minimum required circuit size is also the maximum required required circuit size.

As the NEC is a MINIMUM standard it is saying that this is the smallest circuit that is allowed for a range 8 ? KW and larger.

Now that I agree with.

40 amps is the minimum size required.

If the load is higher than we have to exceed the minimum.

Ever seen a 60 amp range cord?
What is the largest range cord you ever saw?

Nope, the largest I have seen is 50 amps.

That means nothing.

It certainly does not prove your point.