Residential Load Calculation

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etszap

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I'm doing a residential load calculation to show that a 30kw generator is sufficient to carry the total load.

Note: Service consists of (1) 320A meter can feeding (2) 150A Service rated automatic transfer switches.
3459 Sq ft, (2) Appliance, Laundry, 8kw range, 5kw dryer, 3kw water heater and A/C w/10kw heat.

I used 220.82 and ended up with 29kw and change after demand and with heat @100%.

County turned it down because 220.82 states that "This section applies to a dwelling unit having the total connected load served by a SINGLE 120/240-volt or 208Y/120-volt set of 3-wire service or feeder conductors with an ampacity of 100 or greater."

In talking to one of the processors, their take is that since I have (2) separate mains feeding the house 220.82 does not apply.

My interpretation is that there is but one service to the dwelling, and that both feeders are fed from that single service and that the calculated load for the entire service is what both the incoming power and the generator will see.

Been in the trade awhile and have never had to ask how many mains a residence will have before doing a load calc.

Input?
 
The problem is the code says served from a single set of 3 wire service or feeder conductors. You state that you have 2 sets of feeder conductors.
I would do the calac based on 220.40 and be done with it.
 
main

main

I do not completely understand your situation, if you have one service drop leading to a meter module with or without a main, code allowing up to six disconnecting means, although in your case separated into two (sub feeds) this is still a single service only one service lateral exists if I understand it correctly your load calculations for an additional or one generator for all would correspond to the connected load to be supplied. I believe as well your calculation would be based on 220.40
 
Jomaul said:
The problem is the code says served from a single set of 3 wire service or feeder conductors. You state that you have 2 sets of feeder conductors.
Click to expand...
I disagree. Emphasizing the words ?feeder conductors? does not alter the fact that the word ?OR? is part of the sentence. It says ?service or feeder.? There is a single set of service conductors; that is all that matters. I believe your proposed design was compliant.
 
Charlie he states he has 1 meter can with 2 sets of feeder conductors feeding 2 disconnects. There would be 2 sets of service conductors not 1
 
I think that means you can't apply the calculation to just one of the panels. But the sum of all loads works it way up to a single service drop or lateral.
 
Calculation by Feeders-220.82
Feeder #1
1729 Sq ft X 3 = 5187
Appliance = 1500
Laundry = 1500
Dryer = 5000
Subtotal = 13187
1st 10kw @ 100% = 10000
Remainder @ 40% = 1275
Total feeder demand load = 11275
Heat @ 100% = 10080
Total Feeder #1 21355

Feeder #2
1730 Sq ft X 3 = 5190
Appliance = 1500
Range = 8000
WH = 3000
Subtotal = 17690
1st 10kw @ 100% = 10000
Remainder @ 40% = 3076
Total Feeder #2 13076
Feeder #1 & Feeder #2 34431
---------------------------------------------------------
Calculation for Service using 220.82
3459 Sq ft X 3 = 10377
Appliance(2) = 3000
Laundry = 1500
Dryer = 5000
Range = 8000
WH = 3000
Subtotal = 30877
1st 10kw @ 100% = 10000
Remainder @ 40% = 8351
18351
Heat @ 100% = 10080
Total Service 28431

The difference between the two calcs is 6 kva - it should not make a difference whether there is (1) Main exceeding 100A or (2) Mains exceeding 100A as far as the overall service calculation.
 
The optional calculation is supposed to use nameplate values. Is your range really 8KW, or did you use the range demand table? You can't use the table, and I'd expect a value more like 12KW since most ranges are in the 10 to 14 KW category.

Also, is your water heater really that small? I've never seen a normal one less than 3600W?

I still think you can do the whole service calculation using the optional calc. Even if you up the range to 12KW, you've got plenty of room for growth. You just may need to use the standard calculation when doing each feeder to make sure it doesn't exceed 150A (and make sure to switch back to the range demand table when using that).

If this is the true load, why did they have you install a 300A service?
 
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