branch ckt sizing of electric ranges

[copper123]

Hello,
I am doing a little rewiring on a house and the owner has found a very old double oven/range with burners on the top that he wants to reuse.
The nameplate on the appliance says
115/230
120/240
KW=20.9
I have been trying to size this old monster and have come up with a few calcs.
I can use table 220.19A for a single oven, However it appears that it is over 12KW so I need to use the nameplate rating.
My KW is 20.9 so
20.9 x 1000 = 20900
20,900 /240 volts = 87 amps
If I go to branch ckt rating, 210.19A3, it tells me that the conductor for househod ranges shall have an ampacity not less than the rating of the branch ckt and not less then the max load to be served.
If I go to 422 for appliances, it tells me to use 220.19 and nothing about using 125% for my loading.
My first question. Am I not reading the table correctly for 220.19. If I am over 12 KW for one range, do I not use column C or can I use note 1 and still use the C column.
If I can use note 1, I come up with this for my range.
5% for each KW over 12.
so, 21 KW is 9 Kw over 12
so 5% for each Kw over 12 is = 45%
so max demand one range column C is 8 Kw
8 KW x 45% = 11.6 KW
11.6 KW /240 = 48.3 amps
It looks like I can run this with #6 and fuse with a 50 amp OCPD
Thanks for any help!
Also, how does the 120 volt power come into play on a range. Do the burners on the top use 120 volt power? And do you always calc you amp draw using 240 volt loading?

 

[George Stolz]

Re: branch ckt sizing of electric ranges

11.6 KW /240 = 48.3 amps
It looks like I can run this with #6 and fuse with a 50 amp OCPD

Looks that way to me.

Also, how does the 120 volt power come into play on a range.

Generally speaking, I think it's just the clock.

And do you always calc you amp draw using 240 volt loading?

The nominal voltage of any appliance, yes.

Edit to add: Notice note 4:

4. Branch-Circuit Load. It shall be permissible to calculate the branch-circuit load for one range in accordance with Table 220.55. The branch-circuit load for one wall-mounted oven or one counter-mounted cooking unit shall be the nameplate rating of the appliance. The branch-circuit load for a counter-mounted cooking unit and not more than two wall-mounted ovens, all supplied from a single branch circuit and located in the same room, shall be calculated by adding the nameplate rating of the individual appliances and treating this total as equivalent to one range.

It's an odd sounding appliance, so I'm just throwing this in, in case I am picturing the wrong thing.

[ March 02, 2006, 08:08 AM: Message edited by: georgestolz ]

 

[jwelectric]

Re: branch ckt sizing of electric ranges

You might want to take a look at 210.19(A)(3)

(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.


Why install more than is required? My range has benn on a 40 amp breaker for over 40 years with out any problem.

[ March 02, 2006, 09:04 AM: Message edited by: jwelectric ]

 

[haskindm]

Re: branch ckt sizing of electric ranges

The 40-amp requirement is the MINIMUM, we often need to exceed the minimum. Read note 1 to table 220.19 (220.55 in 2005 code) for calculating a range over 12KW. I also get a calculated load of 48.3 amps, which would require a 50-amp circuit.