Increasing power to detached garage

[mark2457]

Hi All

the house i bought has a detached garage about 20 feet from main structure. It currently has 1/2-inch rigid metal conduit with a single 20A circuit (3x12ga THHN). I need about 13A for a table saw or router (two are never on together) and 11A for dust collection. Then enough for "small appliances" such as radio, battery charger, and 4ft fluorescent light with 3 tubes.

If I were starting over I would run 3x6ga + ground and add ground rods and a sub-panel with 60A breaker in main panel. I may do this next year or year when I do landscaping, but for now, I want to minimize the expense and effort, as I have a LOT of other projects to fund and do.

What's the best I can get with the existing 1/2-inch rigid metal conduit? I rewired the entire house (was 80% knob and tube and had use EMT as I'm in Chicago), so I have no problems adding to or replacing the existing conductors, installing a sub-panel, ground rods, etc. In fact, I want a sub-panel as I want local circuit breakers.

Ideally, I'd like to have 3 circuits (any combo of 15A and 20A).

IIRC existing conduit is allowed a 40% fill, so could I do 3x8ga (2 hot and 1 neutral + 12ga ground) = 38.93% (Not sure if 12-ga ground is enough, 10ga will push me to 41.x%)



TIA
Mark

 

[sublimate]

Can you use the metal conduit as your ground?

 

[pattenp]

NEC conduit fill table says 1/2" rigid metal is 3 #8's THHN/THWN.

 

[mark2457]

Can you use the metal conduit as your ground?

Not 100% sure what code is here in Chicago

 

[mark2457]

NEC conduit fill table says 1/2" rigid metal is 3 #8's THHN/THWN.

If I'm right, that gives me 55A, so I'm guessing I'd use a 50A DP breaker in main panel (or will they let you go to 60, like they do with 95 to 100) and then 2x15 and 1x20. (Would it be OK to install 3x20A knowing it would trip the main breaker at 50A?

 

[wyliesdiesels]

If I'm right, that gives me 55A, so I'm guessing I'd use a 50A DP breaker in main panel (or will they let you go to 60, like they do with 95 to 100) and then 2x15 and 1x20. (Would it be OK to install 3x20A knowing it would trip the main breaker at 50A?

#8 THHN is only good to 50a. The 90* c ratings are for derating purposes.

And u wont necessarily trip the 50a main breaker with 3 20a breakers in the subpanel. It all depends on your actual load.

 

[pattenp]

The 3 #8's is based on that the conduit can be used for the equipment ground. If not, then 3 #10's and a #12 for the ground can be used, but that limits you to 30 amps.

Is that 1/2" conduit buried deep enough? At least 18".

 

[mark2457]

The 3 #8's is based on that the conduit can be used for the equipment ground. If not, then 3 #10's and a #12 for the ground can be used, but that limits you to 30 amps.

Is that 1/2" conduit buried deep enough? At least 18".

It's close to 18". Didn't measure, but it's a way down.

I can't find anything definitive about being able to use the conduit as ground back to main panel. I wish they'd write the NEC code in plain English. Apparently even inspectors have different views on this. Plus, our local inspector is a jerk. I had my panel replaced and the inspector refused to tell my sparky how much of old bx had to be replaced to pass the inspection.

 

[SALIV8]

Not 100% sure what code is here in Chicago

I would not use the conduit as a ground as the conduit will rust and rot away and wont be safe. Code will not allow this anyways, as I understand.

 

[Cougar]

It's only 20ft.
Dig a new trench bury some 1 1/2" pvc conduit.

But call diggers hotline first.

 

[Zeke]

It's only 20ft.
Dig a new trench bury some 1 1/2" pvc conduit.

But call diggers hotline first.

I'll bet it's at least partially under concrete or he wouldn't be asking.

Diggers Hotline for 20' between the house and the garage? Do you call DH when you plant a bush? I might if my service was underground and coming at the house where I want the bush. Only house I owned that had the service underground had it 4 feet down as it was direct bury.

But if there's any question I suppose you are right.

 

[aandpdan]

Is there room in existing main panel to add 3 circuits and just pull 6 #12's through the EMT? I feel fairly confident you wouldn't exceed fill rating of pipe. They also make "piggy back" breakers that are 2 breakers that are molded together and are the size of 1 standard breaker. That may help you if don't have room for 3 breakers. If that would work it would get you by until you dig a new trench for the larger pipe.

That violates Code. He can only have one feeder to a detached structure.

If it is 1/2" I'd go the #10 and run a 30 amp subpanel. It will meet his needs for now.

 

[justsam]

Is there room in existing main panel to add 3 circuits and just pull 6 #12's through the EMT? .

Garage is detached. Multiple circuits are not allowed. Ok if attached.

 

[pattenp]

That's why you shouldn't recommend something that's allowed locally in your area of Alabama to someone in Chicago? It's best to cite NEC regulations with a caveat to local exceptions.

diferent rules for different places. It is allowed where I live and that is why I mentioned it. Buddy of mine just did it at his place since he was going to either cut his driveway or run conduit and cable an extra 200' to prevent cutting driveway. Checked with inspector and got the go ahead so we pulled em in. Sub panel is obviously best choice was just offering a quick fix option.

 

[Cougar]

I'll bet it's at least partially under concrete or he wouldn't be asking.

Diggers Hotline for 20' between the house and the garage? Do you call DH when you plant a bush? I might if my service was underground and coming at the house where I want the bush. Only house I owned that had the service underground had it 4 feet down as it was direct bury.

But if there's any question I suppose you are right.

Yes it could be under the sidewalk or driveway, didn't think of that.
Could still run it under a sidewalk without a lot of trouble, but a little extra work.

Thought since he bought the house, may not know what's running where.
Then he would know where everything is.