Sub Panel in new Garage

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  #1  
Old 09-28-06, 03:34 PM
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Sub Panel in new Garage

I am building a detached garage and I want to put in a 50 AMP sub panel. I was thinking that I might as well put in wire suitable for 10 0 AMPs in the case that I ever need to upgrade. Anyway the distance from the service panel in the house to the garage is 200' and the wire needs to be underground. What Gauge/type wire should I use? In addition, what size conduit would I have to use?
 
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Old 09-28-06, 04:34 PM
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You will need to do a couple of thing in addition to just the panel and wire, you need no ground wire because you will be installing a ground rod at your garage

#2 copper x 3 conductors 2 hots and a neutral
and a 1 1/2 pvc pipe

no code book in front of me though so this is a educated guess on the wire size
 
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Old 09-28-06, 05:04 PM
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You WILL need a ground if you have any other metallic path between the two buildings, such as a telephone wire, cable TV wire, etc. Even if you do not have such a path yet, I suggest that you anticipate one and add the ground wire.

The size wire will depend on the amount of current you actually want to pull. 200 feet is a long way.
 
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Old 09-28-06, 05:27 PM
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Thanks for the Reply

Can the metalic path that you refer to use the same conduit? If not, then I can say without hesitation that there will be no additional metallic path. My current requirements today are nothing but a few lights, some power tools perhaps a table saw, however I wanted to make sure that if I have a dust collector and a compressor and the table saw and........I am sure you get what I mean. I priced out the #2 wire (that's what I was thinking as well) earlier today and with 3 strands the wire alone was nearly $ 1,200.00! The ground wire would add another $400.00.
And by the way, the sub code official in the town was telling me that they want to see grounding to the rebar in the concrete footing rather then a seperate grounding bar. Have you ever heard of this?
 
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Old 09-28-06, 06:51 PM
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Originally Posted by rso44
And by the way, the sub code official in the town was telling me that they want to see grounding to the rebar in the concrete footing rather then a seperate grounding bar. Have you ever heard of this?

I believe this is referred to as a "Ufer" ground. You might search this forum, as I believe it has been talked about here in the past. If you don't find anything here, Google it...there's plenty of info on that method out there.
 
  #6  
Old 09-28-06, 09:25 PM
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Yes I have heard of it, the idea, I reason, is that your whole rebar system in the foundation becomes the ground

the no grounded metalic path is more specifically the no continuous metallic path BONDED to the grounding system of BOTH structures

this does not mean you can't take cable tv -you just would not bond it to the second building electrical service and not have any other grnd paths ie. water pipe, gas pipe, metal pipe

two hots and a neutral w/grnd bar are code compliant 250.32(B)(1)

also a rule of thumb to use is always go up 1 wire size every 2 hundred feet
 

Last edited by william tell; 09-28-06 at 09:38 PM.
  #7  
Old 09-29-06, 04:25 AM
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rso44,

In your building you need to ground the panel because this is a detached structure with a panel. This is easiest done with a groiund rod. However, you must also incorporate certain other items into the ground. Sometimes these other items are part of the ground, other times they are items bonded to the ground. Items includes rebar in concrete, the steel shell of buildings, etc.

As for the ground wire between the buildings (between the panels). Go ahead and leave it out, but only if you do not and never will have anything else metallic between the buildings. If you have a water pipe, a telephone line or any other path between the buildings then you MUST have a ground wire with your electric line. It does not matter what those wires connect to in the building, if they go between the buildings they count, and force a requirement for a ground wire.
 
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Old 09-29-06, 09:23 AM
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Smile

I would use a 100 amp 4 conductor aluminum feeder. The box stores carry a 2-2-2-6 direct burial (24") cable that's normally used for mobile home feeders. It's a pre-twisted cable consisting of 4 individual conductors without a overall covering. The price is around $2 per foot.
The re-bar (Ufer) grounding electrode that you're talking about is accomplished by bonding (using a listed clamp) a #4 copper conductor to the reinforcing steel in the footers before the concrete is poured and then connecting the #4 copper to the grounding bar in the sub-panel. The re-inforcing steel has to be a minimum of a 20 feet length of 1/2" diameter bare steel or electroplated rod (no plastic covering) that's placed within and near the bottom of a concrete foundation or footer that is in direct contact with the earth. It must be encased in at least 2" of concrete. I would also use (steel) tie wire to tie all of the re-bar in the footer together.
hope this helps
steve
 
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