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Old 01-19-2011, 01:24 AM   #1
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2600 foot run, 400 amp undergound????


I am wondering what a 2600 foot run (that is from main line to house) should/could cost including trenching. I need 400 amp service. Pole split 200 for house and 200 for shop/MIL would cost. I am in northern CA. Power company says they want me to go underground because driveway is not strait and would use to many poles to make it cheaper. Also power run starts across neighbors prop for 1000 feet of it and he insists on underground. PG&E (power company) also says no one else has enough insurance to run the lines themselves.

ANY input/advice/price est. is great.

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Old 01-19-2011, 03:37 AM   #2
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2600 foot run, 400 amp undergound????


Such a run should be done at primary voltage, with the secondary transformer located near the metering point.

You are suggesting a half-mile of cable here .... !

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Old 01-19-2011, 08:17 AM   #3
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2600 foot run, 400 amp undergound????


You will want something in writing from the neighbor, perhaps paying him rent for running the line across his property. An easement, usually involving a one time fee, would be more favorable for you. Or maybe you or the power company already have such an easement.

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primary voltage, typically 7000 to 15000
The cost of cables to run 120/240 volts (i.e. secondary voltage) at 400 amps that distance, overhead or underground, would be tremendous as the cables would have to be very fat to not suffer massive voltage drop.

400 amps at 240 volts is about 14 amps at 7000 volts. A 3% voltage drop at 7000 volts is about 200 volts. The round trip of about a mile can have up to 13 ohms (of resistance) to stay within that voltage drop. Probably the minimum wire size the power company will run is 8 gauge copper and with that, the round trip is about 4 ohms.

Whereas 3% voltage drop at 240 volts is 7 volts. If a draw of 300 amps between the two buildings is not out of the question, you are allowed only 0.025 ohm for the round trip to have a voltage drop within 3%. (Voltage drop equals current times resistance). My copper resistance table only goes down to 1/0 AWG gauge and the resistance is 0.1 ohm for 1000 feet or half an ohm for the round trip, twenty times what was allowed. I am guessing we need 1100 square millimeters or 1-1/2 inch diameter copper (one AWG size larger whatever that corresponds to in aluminum, perhaps 2 inch).

And the primary run needs two conductors, hot and ground. The 120/240 run needs four (the ground doesn't have to be as fat).
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Last edited by AllanJ; 01-19-2011 at 09:58 AM.
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Old 01-19-2011, 09:32 AM   #4
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2600 foot run, 400 amp undergound????


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Originally Posted by gearedup View Post
I am wondering what a 2600 foot run (that is from main line to house) should/could cost including trenching. I need 400 amp service.
I don't think you have a much choice. You will have to pay what PG&E charges so ask them for an estimate. You don't want your point of connection 1/2 mile away from your house.
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Old 01-19-2011, 11:41 AM   #5
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2600 foot run, 400 amp undergound????


If I want power on grid - which I do because of comforts and need I have to make the run - but is there any way to make it cheaper; I was thinking about calling a large scale elecrtical contractor and seeing what they would do the whole job for - I think Poco just supplies transformer and hook up. - can I do that - do you think cheaper? Excavation company wanted to charge 60K and poco said another 75K to run line. Seems out really out of line to me - gotta make it cheaper.
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Old 01-19-2011, 12:07 PM   #6
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2600 foot run, 400 amp undergound????


often times the POCO will be cheaper than anybody else. They are going to be your provider so often there is a discounted installation to get you to become a customer. In my area, anything prior to the meter is POCO property and responsibility so they demand they install it. You don't get a choice.
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Old 01-19-2011, 12:55 PM   #7
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2600 foot run, 400 amp undergound????


You might be able to get someone else to dig the trench. But this may make the job take longer due to scheduling, logistics, and having the electric company inspect and approve the trench.
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Old 01-19-2011, 06:13 PM   #8
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2600 foot run, 400 amp undergound????


It is a lot of money !
But, you gotta understand thats a long distance
and that involves large conductors,
copper is very expensive so is aluminium.
Some one has to pay for it .
Perhaps running a higher voltage will enable
lower currents so smaller cables.
But I think your up for a large chunk of change either way.

Quote:
Originally Posted by gearedup View Post
If I want power on grid - which I do because of comforts and need I have to make the run - but is there any way to make it cheaper; I was thinking about calling a large scale elecrtical contractor and seeing what they would do the whole job for - I think Poco just supplies transformer and hook up. - can I do that - do you think cheaper? Excavation company wanted to charge 60K and poco said another 75K to run line. Seems out really out of line to me - gotta make it cheaper.

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