Cable size vs. distance

[SparkyMc Sparkface]

Hello all. Long time lurker, first time posting a question...

I am constructing a three-car, 1,650 sq/ft detached garage for residential/ private use in Northern Virginia. There is a split 400 amp service located 375 feet away in an existing outbuilding. The split service serves 200 amps at the outbuilding, and the remaining 200 amp service is for feeding the new detached garage. Therefore, we will have a 200 amp sub-panel located in the new detached garage with main disconnect located in the outbuilding.

The main service disconnect is 375 feet away. The detached garage will have a car-lift, commercial wood shop equipment, lots of lighting, and a mini-split heating/cooling system. We have estimated approximately 80 amps continuous load.

Our main concern is voltage drop over such a long distance. I have complete confidence in my electrician, however feel an obligation to my customer to verify correct load vs. voltage drop calculations.

Here is my question: What size feeder cables should we use to feed a 200 amp sub-panel 375 feet away with min. 80 amp continuous load?

Thank you in advance for your time.
Matt

 

[Jraef]

I can't speak for all of the Moderators, but technically you would not be allowed to post (General contractor) however since you indicate you have an electrician doing it, I won't close the thread.

In short though, there are numerous mitigating circumstances involved in conductor sizing in addition to the minimal info you posted. Is the 375' the sight line distance, or the down-over-up conductor length? Is he using copper or aluminum? What type / rating of insulation? Underground, overhead, direct burial, in conduit? Is the 80A estimated load inclusive of future plans? If so, why allot 200A for it then?

Bottom line, I always feel it's better to do it once and over build a little. If you size it based on the 80A projected load and you change your mind later, there is nothing more expensive than RE-running conductors...

I would use 4/0 copper and be done with it. UF cable would be good for 195A direct burial or in raceway.

 

[infinity]

According to my Southwire app it would be a minimum of #2/0 copper in conduit, 375', 240 volts, 2.7% voltage drop.

 

[kwired]

Depends on how much voltage drop is tolerable.

According to my Southwire app it would be a minimum of #2/0 copper in conduit, 375', 240 volts, 2.7% voltage drop.

with that 2.7% and 2/0 copper - the 200 amp feeder in this application requires 3/0 copper minimum - so actual voltage drop will be even less.