Residential T-former feeding two existing houses

[Dirt merchant]

Hello, a residential x-former currently can handle the two houses it is suppling, 300a each, 600a total. One house is a small pool house. PSE@G has given me the go ahead to add a 100a panel for outdoor lighting. My question is: the current location of the x-former disrupts the new landscape plans, and the homeowner wants it move up to the road. This will be 250' farther away, and the pipe installed from existing x-former is 2 1\2". I was doing CM= (12xDxI)2 / 3.6 to find the CM of the wire to be used for the new location and noticed in "Table 8" 250 awg and larger wires have a "---" in the CM column. So how do I size my wire to refeed the two houses from the new x-former location? Here are some numbers,
HOUSE #1 500' away 300amp service
HOUSE #2 650' away 300amp service
New Meter @outdoor lighting house 300' away 100amps
Thanks for you time :wink: [/list]

 

[bob]

Fro Conductor size 250 and up just multiply the size by 1000 for CM
250 x 1000 = 250000 CM. If you are considering providing service to a
house from 600 ft you are asking for trouble in my opinion .

 

[bdarnell]

Your formula looks basically correct. The constant "K" that is typically used is 12.9 but based on the ambient that the wire will be installed, 12 probably works. Also, your drop can be for 240 V, assuming that's what you have.

I get around 700 kCMIL if you want to keep a 3% drop based on 240 V and 300 amps.

 

[dereckbc]

Actually you can drop "K" down to 11 or less. 12.9 is very liberall as is 11. I have data from thousands of audits and have never found "K" to ever be above 10.