Residential service load calculation

nizak

Senior Member
Opinions please.

I have a new build that has a calculated service load of approximately 145 amps .Current job spec calls for a 200 amp service (120/240V single phase)

Would this current value (145) be enough to entertain the thought of a 400 amp service instead?

I don't want to sound like I'm trying to up Cost the job by suggesting the upgrade.

Suggestions/ thoughts appreciated.
 

nizak

Senior Member
I would agree about that so that means 145/2 = 72.5 amps so why would you want to go up to 400 amps?
The job was bid by another contractor and the owner was told due to the size of the house a larger service would be advised.The 200 amp spec was listed on the drawing of the house and was most likely put on there by the designer and not an engineer.

I was not told what the other contractor figured the load to be.
 

flashlight

Senior Member
Location
NY, NY
If the calculated load is 145A it's likely the real load at any one time will be half that or less, unless there is a lot of electrical heating.

IMO, 400A would be way overkill unless he has future plans for a welding business.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
Talk to the home owner's and see what they forsee in the future and let them know the cost difference. One thing you can do is install a 400 amp (320 amp) meter base and just use one side. If they decide to upgrade you can always add a panel to the other side of the meter.
 

nizak

Senior Member
Talk to the home owner's and see what they forsee in the future and let them know the cost difference. One thing you can do is install a 400 amp (320 amp) meter base and just use one side. If they decide to upgrade you can always add a panel to the other side of the meter.
Owners don't foresee additional loads.

Good point. I'm not certain but the POCO may require justification of the 400 amp meter base to even be installed.



Talk to the home owner's and see what they forsee in the future and let them know the cost difference. One thing you can do is install a 400 amp (320 amp) meter base and just use one side. If they decide to upgrade you can always add a panel to the other side of the meter.
 

nizak

Senior Member
If the calculated load is 145A it's likely the real load at any one time will be half that or less, unless there is a lot of electrical heating.

IMO, 400A would be way overkill unless he has future plans for a welding business.
No electric heat
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Engineer
Here, for underground services, our POCO wants a meter base that will take a 3" conduit and specifies the minimum depth of the meter base (4.125"). The 400A ones meet that requirement. The cheap 200A ones are the home center will only take a 2.5" conduit and aren't allowed anymore, and the Home Depot 320/400 meter base is cheaper than the 200A meter base at the local electrical supplier (but I get no discount there). I see no reason the POCO would not accept a larger meterbase even if the main breaker is 200A or less. They get more money for a larger service, and even if they run larger wire to you, the customer pays for that too.

The only reason I see to do a 400A service would be if they want the ability to switch between gas and electric appliances. The price per BTU of each can change a lot, so that is an added flexibility. But they will need to pay for all those extra electrical branch circuits if they want them for water heating, space heating, oven, etc. Some of the heat pump based appliances can be cheaper to run than gas, but I don't think they last as long and they cost more upfront.
 

growler

Senior Member
Location
Atlanta,GA
The job was bid by another contractor and the owner was told due to the size of the house a larger service would be advised.
You can have a small house with a much larger load than a big house.
Learn to look for the major loads, water heaters (especially tankless), electric ranges, dryer, hot tub, vehicle chargers, A/C units and any electric heater if larger than A/C load.

A couple thousand square ft. of general lighting load doesn't add up to much but just one tank-less water heater can change everything.

When doing a load calculation try not to miss any major loads.
 

mwm1752

Senior Member
Location
Aspen, Colo
you should feel comfortable about the correct load calcs - POCO might have issues with excessive service , NEC doesn't restrict you, customer is always right when requesting above & beyond code.
 
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