New Residential service, huge voltage drop.

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Npstewart

Senior Member
Im doing a voltage drop calculation for a residential service. Its not very often I do these for residential. The one way length is about 1550 feet to the transformer, the house has a 400A service. When I run the calc for 320 amps, 1550 feet, and with parrell 3/0 copper, the voltage drop comes up at about 11.2%, approximately 26.97 volts dropped.

My question is should I be shooting for a maximum of 3%?

Even if I use parrell #500s, im still going to be around 7% or so, can a residential 400A meter accept wires this large? It doesen't seem practical.
 
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Npstewart

Senior Member
27 views and no suggestions :-(

I think we will be talking to the POCO to see what other options there are.

In order to get a voltage drop of 3.7%, we would need to use (2) runs of #700s, or (4) runs of #350s, I don't think that would be very feasible.

I changed my calc to use 300amps instead of 320 amps, which is a lot closer to the load calc value.

Id be happy to hear any suggestions, thanks.
 
cadpoint

cadpoint

Senior Member
Location
Durham, NC
Where's the client in all this? One point being are they going to add a barn, a work shed with a welder a Jacuzzi to go with pool?

I know we don’t layout for future usage, but you’ve dropped your own load calculation, how can you do that?

Another point is that your only giving them the calculated amps of their house granted, but the owner will only remember four hundred amps, I‘d be sure to explain this one situation to them. Some call it that moment that turns into selling the service!

If they build in the woods they can usually afford to have available additional power, I’d get closer to the four hundred amps. I know I’d hate being the deer in the headlights later if you don’t explain this situation now, and they wanted to add something later. JMO
 
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
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rcwilson

Senior Member
Location
Redmond, WA
My 4500 sqft home is only 350 feet from the transformer. My contractor saved money 20 years ago by putting in a 200 A service with 350 kcmil cables UG. Utility wanted about $17,000 to add a transformer near the house.

All hot water heaters and furnace are gas powered, including the hot tub so the load stays within reason on the 200A service.

Lights still dim when a large appliance starts. My wife complains because we can't add a heat pump or air conditioning. Nor can I add an electric tank-less water heater or build that wood shop of my dreams on the back 1/2 acre.

Morale: Tell the client to pay for a utility transformer at the house or plan on lowering their expectations, their future contentment and their load to 200 A or less. They won't be happy with the low voltage.
 
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Npstewart

Senior Member
The calculated ampacity demand according to the load calc is 275.0 amps, so we went to a 400A service. I used 300 FLA in my calc to be on the safe side.

We already have considerations for a barn in the load calc, but that is a great point.

I think the general consensus is that we need to talk to the POCO.
 
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One-eyed Jack

Senior Member
Location
Scotland Neck, NC
Npstewart said:
The calculated ampacity demand according to the load calc is 275.0 amps, so we went to a 400A service. I used 300 FLA in my calc to be on the safe side.

We already have considerations for a barn in the load calc, but that is a great point.

I think the general consensus is that we need to talk to the POCO.
Click to expand...

Build service at trans pole. 240/480 tranformer. Run same size feeder at 480v and trans down at house. If you see a 320 amp load at the house it is because he is Jim at Tampa's brother.
 
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