Per T220-19 (note 3) ranges between 1 3/4 kw and 8 3/4kw, for multiple ranges where some of the ranges falls in column A and B, "the demand factor for each column shall be applied to the appliances for that column and the results added together". As an example: say we have 5 - 3kw and 5-5kw ranges (total of 10) I have been told to take the 3kw's at 62% for 5 ranges and 5kw's at 45% also for 5 ranges then add the 11.25 & 9.3 for a total of 20.55kw. I believe it is more reasonable to use the 10 appliance row, and multiply the 3kw's by 49% and the 5kw's by 34% which would total 7.35 for the 3's and 8.5 for the 5's for a grand total of 15.85kw. It seems to me that the total of the 3's and 5's should be allowed to be at the least equal to 10-5kw's which would derate to 17kw if not less. Please let me know what you think.
Residential Range Calculations
- Thread starter edwardgri
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bphgravity
Senior Member
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- Florida
Re: Residential Range Calculations
I do not know the logic either, but for some reason the code does not allow as large of a reduction for ranges under 3.5kw verses those that are 3.5kw to 8.75kw.
It would seem to be a much easier to understand table if Column A and B were just combined.
Your calculations make sense, but that is not how the code allows it to be performed. Your first calculation is the correct one.
I do not know the logic either, but for some reason the code does not allow as large of a reduction for ranges under 3.5kw verses those that are 3.5kw to 8.75kw.
It would seem to be a much easier to understand table if Column A and B were just combined.
Your calculations make sense, but that is not how the code allows it to be performed. Your first calculation is the correct one.
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- Lockport, IL
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- Semi-Retired Electrical Engineer
Re: Residential Range Calculations
I can only guess at an explanation, but it seems reasonable to me. Here goes:
If all ranges were either on or off (i.e., running at either 100% or 0%), then I would agree with your logic. But ranges are seldom run at 100%. Consider Person A as having a 3kW range and Person B as having a 5kW range. Consider Thanksgiving Day - both persons have mid-sized turkeys in the oven and several burners going for the potatoes and other side dishes. The turkeys are both cooked at the same temperature, and would require about the same amount of power to maintain that temperature. The burners are all on low, just keeping the veggies warm. Person A could be using 2.5 of the available 3.5 kW, or about 70% of the available capacity. Person B could be using 2.5 of the available 5 kW, or about 50% of the available capacity.
I know this scenario is pure fiction, but I do believe the point that it illustrates. The lower power ranges are likely to be used at a higher average percentage of their capacity. NEC Table 220-19 accounts for this factor.
I can only guess at an explanation, but it seems reasonable to me. Here goes:
If all ranges were either on or off (i.e., running at either 100% or 0%), then I would agree with your logic. But ranges are seldom run at 100%. Consider Person A as having a 3kW range and Person B as having a 5kW range. Consider Thanksgiving Day - both persons have mid-sized turkeys in the oven and several burners going for the potatoes and other side dishes. The turkeys are both cooked at the same temperature, and would require about the same amount of power to maintain that temperature. The burners are all on low, just keeping the veggies warm. Person A could be using 2.5 of the available 3.5 kW, or about 70% of the available capacity. Person B could be using 2.5 of the available 5 kW, or about 50% of the available capacity.
I know this scenario is pure fiction, but I do believe the point that it illustrates. The lower power ranges are likely to be used at a higher average percentage of their capacity. NEC Table 220-19 accounts for this factor.
bphgravity
Senior Member
- Location
- Florida
Re: Residential Range Calculations
Charlie, this is a great theory and makes complete sense. You have great logic and explain things with great clarity. Thank you.
Bryan Holland
Charlie, this is a great theory and makes complete sense. You have great logic and explain things with great clarity. Thank you.
Bryan Holland
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