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Want to trench electricity up the hill

 
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Location: East flank of the South Mountain, Maryland Blue Ridge
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Hi, I want to trench some electricity up to the top of my hill.  It is probably altogether 300 feet that I want to lay to get it to where I want it.

I've heard that one needs really big gauge, like -0- or -00-, and if that is the case, that is very expensive.

Has any one ran cable of this stretch? is there general rule for the length with the gauge?  I am wanting to send up a 100 amp circuit and split that into one or more 240v and 120v circuits.

Thanks for your thoughts!

Mark

 
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I ran 200 amps about 200' underground in conduit, and used 4/0 three conductors plus ground.

I have run 100 amps about 500' from there in conduit, and my recollection is that I used 2/0, but it was a dozen years ago and I am not positive on the gauge.


For actual calculations, this gives numbers based on all relevant variables. Using your criteria, I get this:


Voltage Drop
2.93%
Minimum Conductor Size
3/0 AWG


1 conductor per phase utilizing a 3/0 AWG Aluminum conductor installed Direct Buried will limit the voltage drop to 2.93% or less when supplying 100 amps for 300.0 feet on a 240 volt 3 phase system.
 
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Yup, that's gonna be expensive. I just ran 30A about 110 feet and I used 8 gauge, which according to a few online wire calculators, was right on the edge of the envelope. I'd advise you to find a reputable (looking) online calculator and go from there.
 
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Is this a new service, or a feeder off of an existing panel? Is this for a dwelling/shop, or why do you need 100amp service?

Direct burial aluminum is probably cheaper, but I prefer copper in conduit. Regardless, I suggest you throw an extra empty conduit in the trench, you can later fish something else through. Also consider if you need water pipes while the trench is open.

Note that if you upsize the conductors for voltage drop you have to upside the ground as well.
 
Glenn Herbert
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I would always run underground wire in conduit, even if not required by code. Between the extra protection and the possibility of replacing easily if ever needed, and the relatively low cost of PVC conduit, I consider it a no-brainer.
 
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