running power to a detached garage in NW Indiana

[wak]

This summer, I plan on running power out to my detached garage.

Conditions: All season weather upper midwest USA. Distance run is about 60 feet. 120 VAC, have not sized current rating yet, lets say 75 Amp as an estimate.

Underground seems more appealing to the eye then overhead and easier to install. From a safety stand point, is underground the way to go also? Or maybe a better question is, what limitations and or liabilities does underground have-if any?

Also, I intend on pouring a sidewalk between the house and the garage. Would i run the conduit next to the sidewalk or under it?

How deep in the ground should the conduit be? For example does it need to be below some type of frost-line?

Thank you.

[Snoonyb]

The sidewalk is your choice to locate.
Yes you need to be below the frost line.

[HayZee518]

For a one way run of 120 volts to a 75 amp load would require THREE #4 cables in a conduit. The conduit would be a 1 1/4 or 1 1/2 inch diameter. Easier way would be to run 240 volts to the garage, the conductor size would be reduced as well as the conduit size. At 240 volt 75 amp - would need 4 #8 conductors to a sub panel.
Cost of fittings would be cheaper too. In either case an expansion sleeve is needed at one end of the run.

[wak]

Hayzee,

let me see if I understand this correctly, please. Your saying to run the 240 because more voltage equates to less current per ohms law.

I would then wire up the single phase 240 as as 120 in the garage. hence the other advantage is if I have a 240 vac air compressor I can plug in as well in a 240 outlet.

Is this correct?

Also what is the considered frost line depth in my part of the country near Chicago?

thanks

[kactuskid]

To help make things more clear, you basically have two choices. You can run a single 120v 20 amp circuit to your garage or you can run a 240 volt service to your garage which would then require a subpanel installation in the garage. This subpanel would then provide numerous 120 volt circuits and 240 volt circuits to supply power for your needs.

And the cable does not need to be buried below the frost line. Since you are in Chicagoland where NM-B cable is not allowed then you probably can't install UF cable either. You'll need to install PVC conduit and run THHN/THWN wires inside, and it would need to be buried 18".

Underground is the way to go here, just make sure you call Miss Dig or Diggers Hotline so they can flag all your utilities first so you don't hit anything.

I would not suggest running the conduit under the sidewalk if you have a choice. Much easier to dig up the conduit if ever need be. And all receptacles in your garage must be GFCI protected. Here's a link that'll show you how to run a single 20 amp circuit to your garage, a 240 volt circuit would be a bit different in that the conduit would terminate to a subpanel instead of a j-box.

http://www.popularmechanics.com/home...t/1275601.html

[wak]

The 240 vac to a sub panel sounds perfect. Spring is almost here and the projects are pileing up.
That Popular Mechanics article is really good, would be a good idea to post that under illustrations.


Thanks guys!

[kactuskid]

If you're gonna install a subpanel at the garage then you're gonna need more instructions than just that previous link. The conduit and wire sizes will be different depending on the size of service you want out there. A 60 amp service should be more than enough unless you're gonna run a ton of things at once.

Go to this link: http://www.selfhelpandmore.com/homew...rage/index.htm and on the left hand side scroll down to where it says:

"PICTORIAL EXAMPLE OF A GARAGE PANEL WITH 3 OR MORE CIRCUITS 240 VOLT 60 AMP, 100 AMP, 200 AMP BRANCH CIRCUIT WITH UNDERGROUND CONDUCTORS WITH AN EQUIPMENT GROUNDING CONDUCTOR RAN WITH THE FEEDER SUPPLYING THE DETACHED STRUCTURE"

It will explain to you that you also need to install a ground rod at the garage along with other pertenent details.