Garage subpanel wiring

[Arky217]

I want to run power to my garage from my house.
I will need (1) 120V, 20 amp circuit for outlets
and (1) 120V, 15 amp circuit for lights.

The total wire run from house main panel
to garage sub panel is 90 feet.

What is the minimum 240V main panel breaker
size that I should use (outlet circuit on
one hot to neutral and lighting circuit on
the other hot to neutral) and what is the minimum
wire size that I should use to keep voltage
drop under 2% ?

Thanks,
Arky

[flyingvan]

  I'd go ahead and run 6 awg and go with 30a anticipating future upgrades.  Is this going to be run overhead, direct buried, or in conduit? Do you have a good ground or will you be running a ground wire back to your main?  If you are going overhead, Aluminum wire, 6 will still do.  Direct burial comes as a single cable.  If it's run in conduit it should be individual wires.http://www.cerrowire.com/voltage-drop-table
   The ground, if run back to the panel, can be smaller---but copper wire is cheaper in a big spool.  You could buy a 500' spool and cut it in 4 pieces (1" conduit will hold it) and just tape the ends with colored electric tape to identify

[Arky217]

  I'd go ahead and run 6 awg and go with 30a anticipating future upgrades.  Is this going to be run overhead, direct buried, or in conduit? Do you have a good ground or will you be running a ground wire back to your main?  If you are going overhead, Aluminum wire, 6 will still do.  Direct burial comes as a single cable.  If it's run in conduit it should be individual wires.http://www.cerrowire.com/voltage-drop-table
   The ground, if run back to the panel, can be smaller---but copper wire is cheaper in a big spool.  You could buy a 500' spool and cut it in 4 pieces (1" conduit will hold it) and just tape the ends with colored electric tape to identify

Thanks for your reply, I think now that I'm going forgo the subpanel
and take the advice of an electrician on another forum.
Since I don't plan on any future upgrades at all,
the plan now is to just run a MWBC (multi wire branch circuit).
From a 2 pole, 20 amp breaker at the main service panel, run (4) 10ga THWN wires
underground through pvc conduit to a junction box in the garage.
One hot to the outlets, the other hot to the lights and garage door opener.
The neutral will be shared since the hots are on different legs of the main buss.
And the 4th wire will go from main panel ground to equipment ground.
12ga would work, but going with 10 for reduced voltage drop,
then from junction box, 12ga to outlets and lights.
Yes, I plan on getting a 500' roll of #10 THHN/THWN from Lowes for $75
which is so much cheaper than by the foot for $.49/ft.

Arky

[flyingvan]

   So basically you're wiring it like another bedroom.  I'm sure you're already going to, but for the sake of others reading this---run a strong string through the conduit so if down the road you need to upgrade (to charge your Tesla, or run a generator feed from the garage back to the house) you'll have an easier time pulling cable.
 

[rick91351]

   So basically you're wiring it like another bedroom.  I'm sure you're already going to, but for the sake of others reading this---run a strong string through the conduit so if down the road you need to upgrade (to charge your Tesla, or run a generator feed from the garage back to the house) you'll have an easier time pulling cable.

That is great advise but another side of this is you do not want to skimp on the size of conduit. 

[flyingvan]

True, but I just downscaled mine---I had 1 1/4" molded through my pour but ran 1" through my trench.  My trench had quite a few bends and turns because I didn't want to cut the very old oak tree roots, and the 1" was pretty forgiving.  If I had a straight trench I might have even opted for bigger than the 1 1/4" though.

[dakramer]

you probably don't want to use a 2 pole breaker for this since if it trips you lose both legs. two single pole breakers if you wire it this way.