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#92993 - 04/22/05 01:04 PM Optional Method Calc
electcontrctr Offline
Member
Registered: 04/07/05
Posts: 15
Loc: Fairbanks, AK USA
Hi,
What is the optional method for a load calc? Can this be used on a sub panel?

I used an online calculator and got the following:

General Light and Receptacle Load
1308sqft x 3VA = 3924VA
________________________________________
Small Appliance Circuits Load
2 x 1500VA = 3000VA
________________________________________
Laundry Branch Circuit(s) Load
1 x 1500VA = 1500VA
________________________________________
Total General Load Less Demand
sum of above less T220.11 demand
sum of above = 8424VA
first 3000 at 100 % = 3000
next 117,000 at 35% = 1898
remainder at 25% = 0
sum less demand = 4898VA
________________________________________
Fastened In Place Appliances Load
Disposal = 1176VA
Garage Door = 1000VA
Dish Washer = 1600VA
Attic Fan = 700VA
Microwave = 975VA
sum less 75% demand = 4088VA
________________________________________
Clothes Dryer Circuit(s)Load
Total dryer circuit(s) load = 0VA
________________________________________
Cooking Appliance(s) Load
Range 9.5kVA
T220.19 Column A = 8kVA
T220.19 Column B = 0kVA
T220.19 Column C = 0kVA
Total calc.d range load = 8kVA
________________________________________
Heating or Air-Conditioning Load
Air Conditioner = 4240VA
________________________________________
Largest Motor Load
25% of largest motor = 1000VA
________________________________________
Total Computed Load
22226 Volt-Amps
________________________________________
Computed Amperage
22226 divided by 240 = 93Amps

-------------------------------------

Is there anyway to get this down so I could connect a dryer to it?

Thanks

Bradley
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#92994 - 04/22/05 03:10 PM Re: Optional Method Calc
markp Offline
Member
Registered: 04/12/04
Posts: 60
Loc: Kent, WA, USA
See NEC 220.30. This usually comes in smaller than the standard calculation. You also must have a service or feeder rated at 100A or more in order to use it (so I think you're OK with a 100A subpanel if its on a 100A feeder).

When I run your numbers with the optional calculation, I get 90 amps including a dryer. This was based on:
3.92 KVA living space
4.5 KVA small appliance circuits
5 KVA Dryer
9.5 KVA range
1.6 KVA Dish Washer
.98 KVA Microwave
1.18 KVA DIsposal
1 KVA Garage Door Motor
0.7 KVA Attic Fan

This comes to 28.38 KVA. The first 10 KVA are 100% and the remaining is 40%. So this reduces the load to 17.35 KVA. Then we add the Air Conditioner at 4.24 KVA giving a total of 21.6 KVA which is 90A.

About the only thing I can comment on your standard calculation you included is what air conditioner amp rating did you use? Was it MCA or FLA+RLA? If its MCA, that already has the 25% factor for the largest motor so you can remove that item from the calculation.
_________________________
Mark
Kent, WA
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