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# Outdoor Electric

#1
08-10-05, 03:44 PM
nick_151
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Outdoor Electric

I'm am planning to bury about a 250ft. run of UF-B wire to the end of my driveway for some lights. First of all, how do I calculate what gauge wire to use to account for voltage drop over this distance. Secondly The location where I need to run this happens to already have the telephone line coming from the street. I have some space to work with but not a lot, and the alternative is to bury through the woods, which is more work then it is worth. How far form the telephone line should this be buried to avoid any adverese effects like RF interference?

#2
08-10-05, 04:01 PM
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Join Date: Sep 2000
Location: United States
Posts: 18,497
The very first piece of information we need is the total wattage of the lights you're going to put out there. That's the key factor in deciding voltage drop. And the lights are going to be incandescent? And nothing but lights on this line?

A foot away from the telephone line is enough.

#3
08-10-05, 04:32 PM
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Join Date: Feb 2005
Location: Harrisonburg
Posts: 744
As John said.....we need to know the total WATTAGE for the lighting at the end of the driveway and if that is the ONLY thing on the circuit.

You can figure this yourself as well if you add up the total wattage for the light(s) at the end of the driveway and do this....

Total Wattage (divided by ) 120V ( Nominal ) = Total Amps
(P.S. You will need the AMPS for the online calculator below )

Now use this link online calculator to assist you.

http://www.electrician.com/vd_calculator.html

Of course if you get confused just post the wattage here and we will be able to take care of the math for you.

Now for FUN SAKE.....lets say you had (1) post light with (3) 100W bulbs in it. Which would be 300W total....

300W ( divided by ) 120V ( Nominal ) = 2.5 Amps

Now by the calculator....250' one way using 12 AWG- Copper UF-B you would have a voltage drop of only 2.1% ( or 2.5 volts )

So basically you want to keep the voltage drop above 3%......so 12 AWG would be the best to run......now for FUN try 14 AWG and see what you get.

Note: The calculator uses 75 Degrees Rating. For the most part in your situation it will not make much of a difference either way for what you are trying to do.

#4
08-11-05, 02:03 PM
nick_151
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Kool. I haven't purchased the lights yet, so I'm not sure on the wattage, but the calculator should help. Also, I had considered a receptacle near the end of the driveway. Mostly for running a battery charger, but I want to be sure it could handle it, if I need it for something else. How much amperage should I figure in to account for this?

#5
08-11-05, 02:13 PM
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Join Date: Sep 2000
Location: United States
Posts: 18,497
A battery charger doesn't use much, but if you put a receptacle out there, it will be too tempting. Somebody will want to put up a lot of Christmas lights out there, run a weed wacker, etc. And that could be trouble. I suggest maybe you just avoid temptation and not put the receptacle out there. The receptacle might raise the wire gauge requirements from #12 to #4 in a hurry, and the cost and effort will start to skyrocket.

For all but small uses (like a few lights), 250 feet is too far to practically run 120-volt power.

#6
08-11-05, 02:25 PM
nick_151
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That's kind of what I figured. That's why I asked...to convince myself that it wasn't the wisest idea. I would know better than to overload it, but someone else might not. Thanks again.

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