Service to Garage

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  #1  
Old 12-02-05, 06:22 AM
Gettinitdone
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Service to Garage

I've got 200 amp service in my house and want to run a circuit with a new breaker box to my garage. If I were to put a new 60 amp circuit in my home panel and run it to the garage with schedule 40 pvc underground about 24 inches what wire would/should I use to make the run to the new box in the garage?
 
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  #2  
Old 12-02-05, 06:28 AM
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Originally Posted by Gettinitdone
I've got 200 amp service in my house and want to run a circuit with a new breaker box to my garage. If I were to put a new 60 amp circuit in my home panel and run it to the garage with schedule 40 pvc underground about 24 inches what wire would/should I use to make the run to the new box in the garage?
4AWG should probably be considered the minimum for a subpanel, especially if you're planning on a 60 amp capacity.

You will find resources that say even 6AWG is possible, but it's better safe than sorry.
 
  #3  
Old 12-02-05, 06:37 AM
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The size of the wire depends on the distance to the garage. (The wire distance.)
 
  #4  
Old 12-02-05, 06:40 AM
Gettinitdone
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Distance to garage

To be safe I estimate the distance to be approximately 60 feet. This is a little high, but safe. Is 4AWG the right wire?
 
  #5  
Old 12-02-05, 06:48 AM
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There are many details of a circuit design that you don't even ask about. Please be sure to read several books on electrical wiring and get the necessary background, so that you don't miss some important detail that you don't even know might be a problem. For example, you don't mention grounding electrodes, the use of SCH 80 for mechanical protection, the disconnect at the garage, proper pulling techniques, etc. To fully describe the installation would require a book; so go out and read the book.

For a run underground in conduit, you need wet rated conductors, for example type THHW or type XHHW conductors. You will often find conductors with multiple ratings, eg THHN/THHW is very common. Just make sure that you get something that includes one of the wet ratings somewhere in the mix.

You will need to run 4 conductors: 2 hots, 1 neutral, and 1 ground.

If all of the terminations are rated at 75C, both in the supply panel and in your new subpanel, then #6 copper is totally fine. If you don't have 75C terminations, then #6 copper is _probably_ fine. #10 is suitable for the ground conductor #4 copper is an increase in size, and will require a corresponding increase in the ground conductor to #8

-Jon
 
  #6  
Old 12-02-05, 08:55 AM
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I'd certainly use #6.
 
  #7  
Old 12-02-05, 09:02 AM
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At 60 feet I too would use #6. I would only consider #4 if the distance were much greater and I really thought I might get close to the 60 amps.
 
  #8  
Old 12-03-05, 11:45 PM
solipsist9
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since this a detached garage, you'll need a ground rod at the subpanel. if there are no other potential electrical paths between the house and the garage (any other wiring, metal pipes for water or gas, for example), skip the ground wire from the house to the garage and simply bond the ground and neutral in the subpanel. a shorter grounding path is a safer path.
john
 
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Old 12-04-05, 05:59 AM
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Originally Posted by solipsist9
since this a detached garage, you'll need a ground rod at the sub panel. if there are no other potential electrical paths between the house and the garage (any other wiring, metal pipes for water or gas, for example), skip the ground wire from the house to the garage and simply bond the ground and neutral in the sub panel. a shorter grounding path is a safer path.
john
I don't agree with this statement. I would always run a ground wire to a detached structure sub panel unless there were a compelling reason not to. As far as the distance statement, the distance is the same whether you run a separate ground wire or not.

Remember that the ground rod and ground to neutral connection are for very different reasons.

You do need a ground rod (or two) at the garage sub panel regardless of which way you go.
 
  #10  
Old 12-04-05, 06:42 AM
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So if there is a ground rod at the house and at the garage and a ground wire run between them, how does all of that come together? The ground and neutral will be connected in the main service panel. In this case should they also be together in the subpanel? Or does the ground rod in the garage attach to a ground bus in the subpanel along with the ground wire from the house and both remain isolated from the neutral bus?
 
  #11  
Old 12-04-05, 08:57 AM
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The NEC permits two different methods of dealing with a feeder to a detached structure.

1) Run a separate EGC (ground wire). At the panel in the detached structure, keep ground and neutral separate (like any subpanel). Connect the grounding electrodes to the ground bus, not to the neutral.

_or_

2) If a number of restrictions are met (Solipsist9 mentioned some), don't run a separate EGC. At the panel in the detached structure, bond ground and neutral, and connect all of you grounding electrodes to the bond point.

Either installation is safe enough to meet code. I am certain that a detailed analysis would show one or the other to be safer in a given particular installation, and I can see circumstances where 2) would be better than 1). Generally on this board we recommend using option 1), in part because while _either_ is quite safe, doing 2) correctly is more difficult and doing 2) incorrectly would result in a significant unsafe condition.

Or does the ground rod in the garage attach to a ground bus in the subpanel along with the ground wire from the house and both remain isolated from the neutral bus?
This is the correct way to follow option 1).

-Jon
 
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Old 12-04-05, 09:15 AM
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Winnie,

I am glad you bought up the (2) options. While the 4 wire is better in many eyes the 3 wire option is still widly used and is allowed by the NEC.

As you stated their are some reasons WHY someone would chose either method but as stated in regards to the minimum safety standards ( NEC ) both are allowed.

I personally do not get into what is safer and what is not....both are allowed and until the NEC removes one in an update it is done on a daily basis but for the DIYer their is less chance of error in doing the 4 wire option because it brings up possibly less obstancles that could come down the road AFTER the installation ( like adding buildings ( metal ) and well too much to go into...
 
  #13  
Old 12-04-05, 10:25 AM
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Originally Posted by Gettinitdone
I've got 200 amp service in my house and want to run a circuit with a new breaker box to my garage. If I were to put a new 60 amp circuit in my home panel and run it to the garage with schedule 40 pvc underground about 24 inches what wire would/should I use to make the run to the new box in the garage?
A very good article to read that covers just about every situation for getting power to a detached garage is located here........


http://www.selfhelpandmore.com/homew...rage/index.htm
 
  #14  
Old 12-05-05, 11:30 AM
Gettinitdone
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Thanks

That is a lot of good information. Roger, that link was more like a book so I guess that satisfies the guy that tells me to go out and get the book. I appreciate your posts.
 
  #15  
Old 12-05-05, 12:57 PM
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Hi, yep thats alot to absorb but pretty much covers all the bases. Your situation is about three quarters through the article.

I also agree with Bob (racraft) that a four wire feeder is the best of the options. I wont argue the point of whether 4 is safer than 3. I think the 4 wire is advantageous in that in the future if you run another conductive path to that garage from your house say a phone/data line or water line the four wire feeder would be required at that point. So might as well run the four wires IMO.

You need to have a disconnect for all ungrounded conductors (hots) very close to where your feeders enter the garage. This can be in the form of a disconnect switch or your sub-panel can serve this purpose. The sub-panel cannot have more than six circuit breakers or you will be required to have a main breaker in the sub-panel. You may want one regardless for convenience. There are some inspectors that will require the main breaker if the panel has the capability to have more than six breakers whether you install that many or not.

I'm not sure what you have looked at as far as sub panels but often it is the same price to just get a 100 amp panel and feed it 60 amps from your breaker in the main house panel. You can always change out the feeders someday if you want 100 amp service, but if you ever need that much then I would change my design.

For four wire feeders if the sub-panel does not come with a grounding bar then you need to purchase one that is designed for your specific panel. It will attach to the back of the panel thru predrilled swaged holes. There are usually a couple places for the ground bar. You will not bond the ground bar to the neutral bar, so dont install a green bonding screw or any strap or jumper from the neutral bar to the metal enclosure or anything that joins the two together. You will notice the neutral bar sits on insulated standoffs. The ground bar attaches directly to the can of the enclosure. Keep things that way.

You will need to drive ground rods (at least one 8 footer) You will need to run a solid copper #6 grounding electode conductor from the ground bar in the sub panel to the ground rod and attach it with an approved clamp. These are called acorns or ground rod clamps. Protect this solid wire with a sleeve of pvc wherever it is exposed and subject to damage. The green ground (equipment ground) of your feeder will also attach to the ground bar of the sub-panel.

Nothing in the house main panel changes.

If you are unfamiliar with the methods for installing the ground rod post your questions and someone here can answer them.

Use schedule 80 pvc wherever the conduit is exposed to damage inside or out. Schedule 40 underground is ok. Use conduit sweeps for transitioning in and out of your trench and consider expansion fittings on your risers if your area is subject to ground swell from cold weather. Use sch.80 coming up thru any slab. You should use 1" or 1 1/4". If you want to pull bigger feeders in someday use 1 1/4". You only need to go 18 inches deep for the trench.

Do not run data/phone cables with the feeder cables.

Good Luck
 
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Old 12-06-05, 05:56 AM
Gettinitdone
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Wow

Roger and others. Thank you very much for you information. I'll study and plan and get the project going in the next couple weeks, and I'll be back with some progress reports and more questions I am sure.
 
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