Feeder Wire Size for Sub Panel for a church's detached garage 150' away from service.

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Davisteam

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Granite City, IL
I'm wondering if I have to use 2/0 Copper for an underground feeder 100A Panel (with main Breaker) to a detached garage, 150' from service, or can I use 1 AWG? The garage is only going to have about four LED light fixtures on inside, two out side lights, maybe a dozen receptacles, and a 240v receptacle for an air compressor.
 
Davisteam said:
James, what about all the other calculations? The ones I'm referring to are the 125% rule in 215.2(A)(1)(a), and also I read about a 20% bump up for every 100'. Just wanting to do my best and save money too.
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The 125% or 80% are factors for continuous loads. Not sure where your getting the 20% bump.

As most residential garages I’m sure you do not have an exact load calculation and probably no continuous loads.

So you just need a conductor rated for 100amperes.. I would not be concerned about VD in your situation at all.

As James stated #2AWG copper is plenty good.
 
Davisteam said:
James, what about all the other calculations? The ones I'm referring to are the 125% rule in 215.2(A)(1)(a), and also I read about a 20% bump up for every 100'. Just wanting to do my best and save money too.
Click to expand...
The 125% rule is for the feeder and the breaker, not just the feeder.

So if you're using a 100 amp breaker, then the continuous load is supposed to be no more than 80 amps.

Starting at that 80 amps, you factor 125% for the feeder, which is 100 amps.

Starting at that same 80 amps, you factor 125% for the breaker, which is 100 amps.

#3 copper is rated for 100 amps.

As @Dsg319 said, voltage drop probably would never come into play. But if you wanted to consider the length, then #2 is more than good. It's rated at 15% more than #3
 
Given the loads mentioned I agree that a 100 amp conductor will probably work just fine. If VD is really a concern I would consider using larger aluminum conductors which will still be a fraction of the price of copper.
 
You have a 100 amp panel, in part because that is what is readily available with an installed main.

What you describe for loads suggests you could possibly get away with only 30 to 50 amp main and never overload it.

Voltage drop is dependent on actual load not the setting of the breaker, I'd only use a 100 amp conductor for this, or possibly even put in a 60 amp feeder breaker at the supply end and run 60 amp conductor. It is still ok to supply that 100 amp main breaker with that.
 
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