Clarifying Table 220.55

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augie47

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Can you explain the question a bit ? Note 3 and Note 4 address two entirely different issues.
 

gutierrjg

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Can you explain the question a bit ? Note 3 and Note 4 address two entirely different issues.

Note 4: says that " The branch circuit load for a counter-mounted cooking unit and no 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 name plate rating of the individual appliances and treating this total as equivalent to one range". Mike its using note 3 for the same setup. The only thing I can think of is the calculation is based on different circuits, but what about the service feeders? I'm missing something here!
Thanks
 

david luchini

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Note 4: says that " The branch circuit load for a counter-mounted cooking unit and no 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 name plate rating of the individual appliances and treating this total as equivalent to one range". Mike its using note 3 for the same setup. The only thing I can think of is the calculation is based on different circuits, but what about the service feeders? I'm missing something here!
Thanks

The calculations in the link that you posted are for dwelling unit "feeder/service conductors."

Note 4 in Table 220.55 is specifically for "Branch-Circuit load."

Mike uses note 3 instead of not 4 in his calculation because he is calculating feeder/service loads, not the individual branch circuit load.
 

gutierrjg

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Here is my confusion David, for a service feeder calcualtions one have to calculate the branch circuit for cooking equipment first!!!. Maybe I should ask Mike himself if I don't get this clear.

Thanks
 

augie47

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I would be in agreement with David's answer.Note 3 and 4 provide answers for different purposes.'
It is odd that the branch circuit could be smaller.
I have encountered situations where Note 3 gives you a higher number than simply using Col.C and the answer was that Note 3 states "permissible to" and not required to.
 

david luchini

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Here is my confusion David, for a service feeder calcualtions one have to calculate the branch circuit for cooking equipment first!!!. Maybe I should ask Mike himself if I don't get this clear.

Thanks

Yes, you have to calculate the branch circuit load to figure your branch circuit sizing. But 220.40 says that the calculated load of a feeder or service shall not be less than the sum of the loads on the branch circuits supplies...after any demand factors...have been applied.

Table 220.55 is giving you the demand factors that can be applies to electric ranges or other cooking appliances.

It's not any different than applying the 75% demand factor for appliances from 220.53, or the lighting demand factors from 220.42.
 

Dennis Alwon

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I totally agree with David. If you look at the first sentence in Note 4 it states use the Table for one range. Suppose you have 3 ranges or ovens etc. This is where Note 3 may come into play. So unless you have one range, one wall oven, or a cooktop with no more than 2 wall ovens, you must use the other notes.

You will not likely see the use of a single branch circuit that feeds a cooktop and a wall oven but it is allowed-- I actually did that once because of space in the panel.

Here is what I did for Note 3

Note 3
Over 1 3⁄4 kW through 8 3⁄4 kW. In lieu of the method provided in Column C, it shall be permissible to add the nameplate ratings of all household cooking appliances rated more than 1 3⁄4 kW but not more than 8 3⁄4 kW and multiply the sum by the demand factors specified in Column A or Column B for the given number of appliances. Where the rating of cooking appliances falls under both Column A and Column B, the demand factors for each column shall be applied to the appliances for that column, and the results added together.
Example 1
6 cooking appliances rated 4 kw, 5 kw, 6 kw, 7 kw, 2@ 8 kw. All fall in the range of over 1 ¾ kw thru 8 ¾ kw so we can use Note 3.
4+5+6+7+8+8 = 38 kw. In Column B for 6 appliances we have 43% demand factor so 38*.43 = 16.34 kw or 16 kw.
Example 2
6 cooking appliances but instead of them all being in Column B some will be in Column A…. 1 kw, 1 kw, 1.5 kw, 4 kw, 5kw, and 6kw.
Now we need to use Column A and B. We use Column A for the 2- 1kw and 1-1.5 kw. 1 + 1+ 1.5 = 3.5kw. For 3 appliances in Column A we have a demand factor of 70%. Thus 3.5 * .7 = 2.45 kw
For the 4kw, 5 kw, and 6 kw we must use Column B 4 +5 + 6 = 15 kw. For 3 appliances in Column B we have 55%.
15 *.55= 8.25 kw. Now we add them together…. 2.45 + 8.25 = 10.7 kw.


Here is my understanding of Note 4

Note 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.

The first sentence of note 4 says we can use Table 220.55—well duh—isn’t that what we have been doing… The second sentence states that we must use the nameplate rating for one oven or one counter mounted cooking unit (cooktop).

Example
An oven rated 5 kw will have a calculated load of 5kw. A cooktop rated 6 kw will have a calculated load of 6 kw. Pretty easy huh. But why isn’t there any demand allowance for these units? When an oven is turned on it will draw the rating of the unit so no demand is allowed. The cooktop does not have an oven to help with the diversity of the load so that unit must also be used at 100% also. It would be unusual to have all the burners going at the same time but it is possible.
The third sentence states that the branch circuit load for one cooktop and one or two wall ovens shall be calculated by adding the kw of all the units together and treating it as one unit.

Example
Calculate the load for one cooktop at 6 kw and 2 ovens rated 5 kw. As note 4 states we will add 6 + 5+ 5 = 16 kw.
From the table in column C we have a demand of 8 kw but we also have to use note 1. 16 kw is 4 kw greater than 12 kw so 5% x 4 = 20%
20% x 8 kw = 1.6 kw
1.6 kw + 8 kw = 9.6 kw
Here is an interesting fact.
16 kw range has the same branch circuit rating as a 9 kw range.
A 16 kw as we have just seen is calculated to be 9.6 kw. 9600/240 = 40 amps
A 9 kw range is rated 8 kw. 8000/240 = 33.3 amps or a 40 amp circuit
Also look at 210.19(A)(3) which states for ranges of 8 34 kW or more rating, the minimum branch-circuit rating shall be 40 amperes
 
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