detached garage

[Cramer]

Hello all, I have a detached garage that I am running power to from my breaker box in my home. I want 100a in my garage. I have a 200a service in my house. The bad part is that the garage is about 140ft from the box in the house. What size cables do I need to run? I already have the ditch dug, going to lowes today. thanks

 

[mrb]

2al with 90 amp breaker. 3 or 2 cu with 100 amp breaker. 8 cu or 6 al for the ground. This is before considering voltage drop. What is your calculated load?

perhaps you know this, but it comes up here often:
you have to run 4 wires from the house to the detached garage. 2 hots, a neutral and a ground. The subpanel in the garage has to have seperate neutral and ground bars, neutral cant be bonded to ground in it. You have to install two ground rods six feet apart. You need a disconnect at the garage, can be a main breaker in the panel or a seperate disconnect.

 

[Cramer]

I don't know the calculated load other than 1 circuit for 15a tablesaw, 1 for a future air compressor, a garage door opener, about 6 other recepts and some flouro lighting. I didn't know I had to run 4 wires, this aint gonna be cheap, I would like to use alum to save some money.

 

[mrb]

I don't know the calculated load other than 1 circuit for 15a tablesaw, 1 for a future air compressor, a garage door opener, about 6 other recepts and some flouro lighting. I didn't know I had to run 4 wires, this aint gonna be cheap, I would like to use alum to save some money.

if you dont have large loads that are going to max out the service (ie big plasma cutter and big air compressor) i wouldnt worry about voltage drop and just install #2 protected by a 90 amp breaker. You will be good up to about 60 amps. To keep voltage drop in check for that distance at full load you would have to run 1/0 AL which is going to cost a whole lot more than #2.

 

[Cramer]

if you dont have large loads that are going to max out the service (ie big plasma cutter and big air compressor) i wouldnt worry about voltage drop and just install #2 protected by a 90 amp breaker. You will be good up to about 60 amps. To keep voltage drop in check for that distance at full load you would have to run 1/0 AL which is going to cost a whole lot more than #2.

So if I use #2 will I be installing 4 seperate wires or 1 big cable with 4 conductors inside? What size pvc? 1 1/2"? Should I get a sub panel for the garage that has a main breaker? I need a 90a double-pole breaker for the house correct? I assume the 100a sub panel will come with all the breakers I need for the garage end. Going to Lowes tomorrow, just wanted to know exactly what to get. Sorry about all the dumb questions.

 

[AussieDan]

#2 al comes as 2-2-2-4 quadriplex (2x 2ga hot, 2ga neutral, 4ga ground), you'll want to go with 2" conduit.

90a double-pole breaker for the house end, you might have trouble finding that at lowes.

100a main breaker panel for the garage, you can get kits with the 100a main breaker panel and a selection of 15 and 20a breakers that are a good deal.

 

[Cramer]

#2 al comes as 2-2-2-4 quadriplex (2x 2ga hot, 2ga neutral, 4ga ground), you'll want to go with 2" conduit.

90a double-pole breaker for the house end, you might have trouble finding that at lowes.

100a main breaker panel for the garage, you can get kits with the 100a main breaker panel and a selection of 15 and 20a breakers that are a good deal.

Ok so I connect the neutral and ground to the neutral and ground buss in the house where all the other circuits are connected? Then I hook the two hots to the 90a breaker. The house end is done? Next I connect the two hots to the main breaker in the sub in the garage? and the neutral and ground to their respective busses? or the ground to the two ground rods first then to the sub? do i have to buy a special ground wire for the rods to the box? I'm gonna do the garage end first. thanks aussie and mrb for all your help

 

[mrb]

Ok so I connect the neutral and ground to the neutral and ground buss in the house where all the other circuits are connected? Then I hook the two hots to the 90a breaker. The house end is done? Next I connect the two hots to the main breaker in the sub in the garage? and the neutral and ground to their respective busses? or the ground to the two ground rods first then to the sub? do i have to buy a special ground wire for the rods to the box? I'm gonna do the garage end first.

you are correct about the house end. You may have to buy lugs for your neutral bar if you dont have two large open holes in it (dont use just any lug, there are application specific parts you have to use).

On the garage end, the feeder comes into the panel. Everything gets landed as you said. The wire for the ground rods goes from one rod to the next then to the ground bar in the panel.

post a pic of the panel on your house (with cover removed)

 

[Cramer]

you are correct about the house end. You may have to buy lugs for your neutral bar if you dont have two large open holes in it (dont use just any lug, there are application specific parts you have to use).

On the garage end, the feeder comes into the panel. Everything gets landed as you said. The wire for the ground rods goes from one rod to the next then to the ground bar in the panel.

post a pic of the panel on your house (with cover removed)

Here's two, Looks like I need two lugs as there is already a wire in each. How much is 140ft of #2

 

[Cramer]

you said I might need to buy extra lugs for my neutral bar. Where does this attach, on top of the lug already there or further up on the bar? Also, won't I need one for the ground bar as well, or will the new wire fit in the smaller holes in the ground bar?
One more question, on the new sub panel in the garage, I DO NOT install the green screw on the neutral bar correct? The green screw is already installed on the ground bar though. The neutral does not get bonded to the box?

 

[mrb]

correct, the neutral bar does not get bonded in the subpanel.

the lugs to put a bigger wire in your neutral and ground bar have a fork thing sticking out of them that goes into 2 holes in the bar. thats why i mentioned they are application specific

 

[Charles (in GA)]

The decal inside the door on your house panel will probably have part numbers for the lugs needed for larger wire sizes on the grd and neutral bars. You might have to go to an electric supply house to find these p/n's but this is the best way of being assured of having the correct parts. Otherwise, depending on the brand of panel, you may have to find a distributor for that brand and see what they can provide.

Some will have large lugs that saddle over the ground bar and are retained by a longer screw in the place of a ground bar screw, some will have the two ears that fit into the holes in the ground bar, depends on the manufacturer of the panel.

Charles

 

[hillbilly1]

Ok so I connect the neutral and ground to the neutral and ground buss in the house where all the other circuits are connected? Then I hook the two hots to the 90a breaker. The house end is done? Next I connect the two hots to the main breaker in the sub in the garage? and the neutral and ground to their respective busses? or the ground to the two ground rods first then to the sub? do i have to buy a special ground wire for the rods to the box? I'm gonna do the garage end first. thanks aussie and mrb for all your help

you are correct about the house end. You may have to buy lugs for your neutral bar if you dont have two large open holes in it (dont use just any lug, there are application specific parts you have to use).

On the garage end, the feeder comes into the panel. Everything gets landed as you said. The wire for the ground rods goes from one rod to the next then to the ground bar in the panel.

post a pic of the panel on your house (with cover removed)

There is a one exception to this advice, if you house is new enough, it may have a main outside, in which the panel inside will be a sub panel too. In that case the Neutral and ground stays seperate, otherwise do as above