i have a 100 amp service with a normal bunch of loads on it, modern kitchen, bath and laundry and garage and lighting. i have not counted up the actual watts being used. without doing that, how can i decide what size of a sub panel can be stuck on there? i need to run about 15000 watts of heaters on three new circuits off of this new sub panel. can i get around counting up the existing load?
load calculation
- Thread starter corona
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kbsparky
Senior Member
- Location
- Delmarva, USA
Nope.
Do the required calculations and post your results here for comment and review.
Do the required calculations and post your results here for comment and review.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
I agree.
kwired
Electron manager
- Location
- NE Nebraska
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- EC
Last edited:
Regularkevin
Member
- Location
- Auburn, WA
Dude, come on! Get your books, pencil and calculator out. You need to provide the data and your findings. This forum is to examine if you did the work right.
These guys will drill you if you mess up, but will help you figure out the mistakes so you can learn.
You can have a 100A sub panel. But your total calculated load is limited to 100A if you lump all the loads together. Since the heaters are going to be 62.5 amps, I don't think things are looking good unless all your other major appliances are gas (e.g. range, water heating, clothes dryer).
The load calculation is relatively simple -- you don't have to look up the watts of everything. There are factors for general use receptacles and lights (3 watts/square foot if a dwelling), a value for 120V kitchen counter and laundry appliances (1500 watts x 3), and then each dedicated electric appliance not already covered (e.g. dish washer, garbage disposal, water heater, clothes dryer if 240V, electric range, space heating or cooling, sump or well pumps, garage door openers).
Then a factor is applied to this total (except for space heating/cooling) once you're over a threshold. Depends on which calculation you use though.
The load calculation is relatively simple -- you don't have to look up the watts of everything. There are factors for general use receptacles and lights (3 watts/square foot if a dwelling), a value for 120V kitchen counter and laundry appliances (1500 watts x 3), and then each dedicated electric appliance not already covered (e.g. dish washer, garbage disposal, water heater, clothes dryer if 240V, electric range, space heating or cooling, sump or well pumps, garage door openers).
Then a factor is applied to this total (except for space heating/cooling) once you're over a threshold. Depends on which calculation you use though.
Hameedulla-Ekhlas
Senior Member
- Location
- AFG
It is difficult to estimate like this. Do calculation just note down all your new load and existing load and add them together and then see does it have that much capacity or not.
220.83
220.83
corona,
Like suemarkp says, unless the house has gas appliances, using a 100A service not knowing the house size and existing electrical loads, adding 15kW is difficult. Calculations in NEC 220.83 for an existing dwelling using extended heating circuits may be optional with electric range and heat as you intend. The first question would be what is the total living sf, the second...what is the kW size of the existing heating system? rbj
220.83
corona,
Like suemarkp says, unless the house has gas appliances, using a 100A service not knowing the house size and existing electrical loads, adding 15kW is difficult. Calculations in NEC 220.83 for an existing dwelling using extended heating circuits may be optional with electric range and heat as you intend. The first question would be what is the total living sf, the second...what is the kW size of the existing heating system? rbj
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