T.220.55 notes and example calculation

L

Larry Bohn

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Location
ashland, oregon
I've been wondering why note 2 to T.220.55 references ranges "Over 8-3/4 KW through 27KW" ranges. excluding those ranges below 8-3/4KW. The example calculation included in the codebook for note 2 includes an 8KW range, raising its minimum KW to 12KW. How can they do this and still comply with the rules of the note? I'm perplexed. Can anyone explain this, or is it a mistake in the book?
 
david luchini

david luchini

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Larry Bohn said:
I've been wondering why note 2 to T.220.55 references ranges "Over 8-3/4 KW through 27KW" ranges. excluding those ranges below 8-3/4KW. The example calculation included in the codebook for note 2 includes an 8KW range, raising its minimum KW to 12KW. How can they do this and still comply with the rules of the note? I'm perplexed. Can anyone explain this, or is it a mistake in the book?
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The Table says to use Column C in all cases except as permitted in Note 3. Note 3 permits the use of Columns A&B for equipment 3-3/4kW and smaller.

So if you don't use the permitted column (B in this case) then you are back to Column C, and notes 1 and 2, as you have equipment over 12kW, and finally you are limited to note 2, as you have equipment less than 12kW.

I think they use "Over 8-3/4kW" in note 2, to give a distinction from Column B. But since Note 2 says any equipment less than 12kW shall be figured at 12kW, if you are not using Column A or B, you would figure anything 8-3/4kW or smaller at 12kW and use Column C, note 2.
 
Dennis Alwon

Dennis Alwon

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david luchini said:
The Table says to use Column C in all cases except as permitted in Note 3. Note 3 permits the use of Columns A&B for equipment 3-3/4kW and smaller.

So if you don't use the permitted column (B in this case) then you are back to Column C, and notes 1 and 2, as you have equipment over 12kW, and finally you are limited to note 2, as you have equipment less than 12kW.

I think they use "Over 8-3/4kW" in note 2, to give a distinction from Column B. But since Note 2 says any equipment less than 12kW shall be figured at 12kW, if you are not using Column A or B, you would figure anything 8-3/4kW or smaller at 12kW and use Column C, note 2.
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But doesn't Note 2 indirectly eliminate anything less than 8 3/4 kw?
 
E

ESolar

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Eureka, CA Humboldt County
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Here are two examples: 20A oven and 30A cooktop, for NPR = 11.6KW.
(A) If wired to one fused box on a single branch circuit (like a range), then they count as a single appliance (from the notes) and they are not in excess of 12KW - use column C for 8KW demand. (If they were in excess of 12KW, one would use column C for 8KW x [1 + 0.05 x (NPR-12KW)/1KW]).
(C) If wired to separate breakers they count as 2 appliances - use C and 11KW.

Why? I could have an NPR of 15KW for two appliances on one circuit and have a lower calculated demand than if I wire on separate breakers/circuits. The separate breakers is clearly cleaner and how it is wired does not change the actual demand/use of the appliances. Can someone explain the logic behind NEC in this case?
 
E

ESolar

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Eureka, CA Humboldt County
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Electrician/Contractor
Also - can't one just tap a single >=40A circuit from 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 8¾kW or more rating, the minimum branch-circuit rating shall be 40 amperes.
Exception No. 1: Conductors tapped from a 50-ampere branch circuit supplying electric ranges, wall-mounted electric ovens, and counter-mounted electric cooking units shall have an ampacity of not less than 20 amperes and shall be sufficient for the load to be served. These tap conductors include any conductors that are a part of the leads supplied with the appliance that are smaller than the branch-circuit conductors. The taps shall not be longer than necessary for servicing the appliance.
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david luchini

david luchini

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infinity said:
Can someone post the actual example?
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Determine the maximum demand for four ranges rated at 8kW, 10kW, 15kW, and 18kW.

Solution

Step 1. Total the range ratings:
12kW (minimum value for 8kW range) + 12kw (minimum value for 10kW range) + 15kW + 18kw = 57kW.

Step 2. Calculate the average rating:
57kW / 4 ranges = 14.25kW

Step 3. Determine the amount of rating above 12kW:
14.25kW - 12kW = 2.25kW

Step 4. Calculate the required demand increase:
5% per kW x 2kW (0.25 kW is not a major fraction) = 10%

Step 5. Calculate the maximum demand:
17kW (Column C demand value for 4 ranges) x 110% = 18.7kW
 
L

Larry Bohn

Member
Location
ashland, oregon
david luchini said:
Determine the maximum demand for four ranges rated at 8kW, 10kW, 15kW, and 18kW.

Solution

Step 1. Total the range ratings:
12kW (minimum value for 8kW range) + 12kw (minimum value for 10kW range) + 15kW + 18kw = 57kW.

Step 2. Calculate the average rating:
57kW / 4 ranges = 14.25kW

Step 3. Determine the amount of rating above 12kW:
14.25kW - 12kW = 2.25kW

Step 4. Calculate the required demand increase:
5% per kW x 2kW (0.25 kW is not a major fraction) = 10%

Step 5. Calculate the maximum demand:
17kW (Column C demand value for 4 ranges) x 110% = 18.7kW
Click to expand...
Sorry I'm so late getting back to the party, thanks for posting the example calculation. We're going to be discussing this in my apprenticeship class in a week or two.
I agree with Dennis, Note 2 specifically states "ranges individually rated over 8-3/4 KW".
I've been looking at this calculation in the book since the 2017 code cycle, it may have been there previously but I no longer have my older code books. Every year it leads to a bit of ????? in my class, I've taught that the note should be strictly followed, a range less than 8-3/4 KW doesn't fit the note.
It's correct that an 8KW range can use column C. If the note allowed an 8KW to be raised to 12KW, I would think it should say "ranges less and 12KW" instead of posting a KW limit. I'm following what David is saying, I'm just not sure about using that logic.
 
tortuga

tortuga

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Oregon
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Electrical Design
Good discussion, I agree with Dennis that any ranges under 8.75 kW would be set to the side when using note 2 or run separately if more than one.
Davids steps look correct to me but I would just input 10, 15 and 18 kw ones.
Step 1 would be 12kw (minimum value for 10kW range) + 15kW + 18kw = 45 kw
Then the rest of the steps would end up at 16.1 kW
Next I would add back in the 8kW to end up at 24.1
 
david luchini

david luchini

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tortuga said:
Next I would add back in the 8kW to end up at 24.1
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So ranges rated 8kW, 10kW, 15kW and 18kW (51kW connected) would have a demand load of 24.1kw......

But ranges rated 10kw, 12kW, 15kW and 18kW (55kW connected) would have a demand load of only 18.7kW?

5.4kW lower demand despite 4kw more connected. I don't believe that is the Code intent.
 
W

wwhitney

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Location
Berkeley, CA
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Retired
tortuga said:
Next I would add back in the 8kW to end up at 24.1
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One appliance still gets an 80% factor in Column B, row 1, so you'd only need to add in 6.4 kW to get 22.5 kW.

However, the problem with this approach is what David just pointed out.

So I think the not precisely written intent behind Note 2 is to take any number of ranges, promote all the ones smaller than 12 kW to 12 kW, then apply the procedure in Note 2.

As an aside, if you have N ranges >= 8.75 kW and M ovens <= 8.75 kW, you have to apply Table 220.55 for ranges and ovens separately, then just add the results? There's no allowance to do a single calculation using the M+N row in the Table?

Cheers, Wayne
 
tortuga

tortuga

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Oregon
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Electrical Design
wwhitney said:
One appliance still gets an 80% factor in Column B, row 1, so you'd only need to add in 6.4 kW to get 22.5 kW.
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You cant use B for one range.
Larry Bohn and I were probably taught by the same people LOL

Here is the example from the 2017 Handbook PDF
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EDIT I should note this is handbook commentary.
 
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W

wwhitney

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Berkeley, CA
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Retired
tortuga said:
You cant use B for one range.
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Sure you can, Note 3 refers to "household cooking appliances" which would include ranges. So if you have ranges smaller than 8.75 kW, Note 3 applies to them.

How to treat non-range household cooking appliances larger than 12 kW seems not be covered by Table 220.55.

Cheers, Wayne
 
tortuga

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
Brain fart your right on that one range.
I remain hangup on the
"For ranges individually rated more than 8 3⁄4 kW and "
part
 
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