??? Wire size for shop ???

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  #1  
Old 05-13-04, 07:10 AM
lrminer
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??? Wire size for shop ???

I want to run electricity to a shop near my house. It is about 250 feet away. I want to have an outlet for a 220 volt, 15 amp compressor then some 110 outlets that will be running a power saw or drill. There will be about 4 100 watt lights.
I asked the electric company about this and they offered to put in a new ple and meter for the small sum of $1500 to $2000 dollars. Ouch!
Can anyone tell me what size wire I should run? This will be underground and on a subpanel off of my house. The man from the electric company said I should only need 30 amps.
Thanks for whatever help anyone can give.
 
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Old 05-13-04, 07:14 AM
phillyguy
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A 30 amp circuit would use 10 awg. But do to the large distance of the run you may want to bump that up to a larger size to help with voltage drop.
 
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Old 05-13-04, 09:20 AM
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Exclamation Effective wire size

The minimum effective wire size for thirty amperes, over a distance of 250', is #6 copper or #4 aluminum. Those sizes will hold the voltage drop to just over three percent. Most of the cost of this new installation will be in the work rather than in the materials. You may want to consider running larger conductors to allow for future expansion of electrical use. Best practice is to hold the voltage drop in the feeder to 3% or less. The total voltage drop should be kept less than 5%. That leaves you only 2% for your branch circuit voltage drop but that should be enough as the distances involved in the shop branch circuits should be relatively short.
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Tom Horne
 
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Old 05-13-04, 11:47 AM
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Tom is right about the major cost being labor.
Your distance will throw this off but a popular feed around here for garages and small shops is 60 amps fed by #6 wire due to being allowed to run a sub-panel off a wire that would normally only be good for 55 amp.
 
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Old 05-13-04, 09:57 PM
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I run number 2 alum with a 50 or 60A breaker for distances similar to those, Very cost effective.
 
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Old 05-14-04, 02:45 PM
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Exclamation Watch your voltage drop.

Run number 1 aluminum for fifty or even sixty amperes in order to hold the voltage drop near to three percent. If you exceed 3% in the feeder you will make life hard on any motor that you run in the shop. There is a real risk of shortening the life of the motors by causing a low voltage condition especially during start up.

A very useful trick is to use an eighty or ninety ampere breaker at the house end of the feeder and then use a Sixty ampere breaker as the building disconnecting means at the shop end of the feeder. In the event of an overload the breaker at the Shop end of the circuit will open first saving you the hike back to the house.

It is a very good idea to run an Equipment Grounding Conductor with the feeder conductors. The code would require that you use a conductor that is increased in size in proportion to any increase in the size of the circuit conductors. So for your sixty ampere circuit the number ten copper or number eight aluminum you would use for a shorter run would be upsized to a number six copper or a number four aluminum.

If you want to radically improve the grounding of the entire system you could run a bare number two copper as your equipment grounding conductor. The larger size makes the entire conductor behave as a grounding electrode. For maximum effectiveness you would bury the bare EGC as deep as practicable and at least thirty inches deep. That is only six inches deeper than you would be required to bury the individual UF or SE conductors that are your most cost effective way to run that circuit. The inspector may still want driven rods but if they bottom out on rock you are allowed to bury them horizontally in the trench if it is thirty inches or more deep.
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Tom Horne
 
  #7  
Old 05-15-04, 10:08 AM
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I agree and would probably run number 1 or better if I was going to do any major work out there, the V drop for motor starting and the 3% figure would only be a factor at full load of 50A though. For that distane I would be quite tempted to shop around a little and buy a thousand ft roll of single conductor and chop into 4 pcs. Even though the GEC would be oversize it certainly wouldnt hurt anything.
 
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