125 amp sub-panel in garage

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  #1  
Old 11-01-07, 12:00 PM
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125 amp sub-panel in garage

I am installing a 125 amp sub-panel in my garage which is in California. I have an 85 foot run of two #2 copper for hot, one #2 copper for neutral and a #8 copper for ground run from my 200 amp main service panel in 1 1/2 conduit buried 24 inches in the ground. I also have 25 feet of #4 copper ground in the cement footings for the garage foundation which will also be connected to the sub-panel. Here's my question, since I have the #4 copper Equipment Grounding Conductor buried in the garage foundation connected to the sub-panel can I use a 125 amp service disconnect breaker in the main service panel to feed the sub-panel or am I limited to a 100 amp service disconnect breaker because the main and sub are only connected with a #8 copper ground wire?
 
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Old 11-01-07, 12:58 PM
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since I have the #4 copper Equipment Grounding Conductor buried in the garage foundation
The grounding electrode conductor is buried in the foundation; the equipment grounding conductor is the #8 from the main to the sub. The function of the two is not interchangeable.

connected to the sub-panel can I use a 125 amp service disconnect breaker in the main service panel to feed the sub-panel or am I limited to a 100 amp service disconnect breaker because the main and sub are only connected with a #8 copper ground wire?
You are limited to 100A by the #8 EGC. If you replace that conductor with a #6, then you may increase the breaker to 125A. Replacing the EGC would be a straightforward job, but do you really need the extra 25A in the garage? One hundred amps is a lot of power for a garage.
 
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Old 11-01-07, 01:20 PM
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As Ben pointed out, grounding is complex. The earth ground (provided by the ground rod and/or the ground in the foundation) is quite different from the ground connection back to the neutral.

The earth ground is to provide protection from external power issues, such as lightning, for example.

The ground connection back to the neutral is to allow fault current to return to the power company, such as would happen if the properly grounded metal shell of an appliance would accidentally get energized.
 
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Old 11-01-07, 07:00 PM
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Pulling a #6 ground

Does anyone have any tips for pulling the #6 EGC in 1 1/2 conduit that already has 3 #2 wire in it if there was no pull cord put in the conduit at the time of pulling the other wires?
 
  #5  
Old 11-01-07, 07:09 PM
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Either pull all the wires out and then put in the ones you need, or use the one you are removing to pull through the new one.

Use plenty of wire lubricant. Have a helper. One of you pulls while the other feeds.
 
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Old 11-01-07, 08:45 PM
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Did I get screwed by HD again?

I greatly appreciate the help and advice given here.
I have been reading other Electrical posts and I am thinking I may have been mislead by Home Depot. I was advised by the HD electrical sales person that I could use the bundled wire he was selling me for a 125A feeder to my garage. The wire he sold me is 3 #2 copper (one with black cover, one white cover and one red cover with a #8 copper ground in a sheathed bundle. His answer was yes I could also pull it through conduit.
Here is a picture of the wires with the sheathing stripped back for installation into the sub-panel. Cut and paste URL
http://www348.pair.com/micman/2.jpg
My understanding after further research is that you can not use bundled wire with sheathing in conduit, it needs to be seperate wires. Is this correct.
The #8 copper egc is not big enough for 125A sub-panel service.
Did I get screwed by the HD saleperson?
Also note I've added Homer Simpson as my avatar.
 
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Old 11-01-07, 09:46 PM
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We'll have to know exactly what type of cable this is to make a determination. Some cables can be used in underground conduit, some cannot. Can you find any of the cable sheathing with printing on it?

My guess is that this cable is type NM (bad) or UF (okay) in a 2-2-2-8 configuration which would be limited to 95A anyway based on the temperature rating. Code would however allow rounding-up to a 100A breaker.

> Did I get screwed by the HD saleperson?

You certainly wouldn't be the first. In my opinion, these stores are really irresponsible in passing off employees who are effectively minimum wage stock boys as "home improvement experts" in everything from wiring from roofing.
 
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Old 11-02-07, 01:27 AM
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Originally Posted by ibpooks View Post
We'll have to know exactly what type of cable this is to make a determination. Some cables can be used in underground conduit, some cannot. Can you find any of the cable sheathing with printing on it?

My guess is that this cable is type NM (bad) or UF (okay) in a 2-2-2-8 configuration which would be limited to 95A anyway based on the temperature rating. Code would however allow rounding-up to a 100A breaker.

Hate to debate with ya guys is the 2-2-2-8 wires if copper THHN/THWN ?? if so that you can go 100 amp very easly but the #8 wire IMO it may be too small for me it should be #6 [ but if this is a alum wire that is diffrent story ]

but if this wires is NOT marked at all then you are restricted to the NM or UF rating and use the 75C rating for this.

also just want to head up many inspectors will be picky on this one if the wires are not marked at all they can not run in the conduct underground because this part it willbe a wet location no question asked.

Merci, Marc
 

Last edited by french277V; 11-02-07 at 01:29 AM. Reason: add info to it
  #9  
Old 11-02-07, 04:44 PM
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Just contacted HD and was told the wire I was sold is 2/3 Romex that is THHN but the separate wires aren't marked as THHN. Guess I will be pulling it out of the conduit.
 
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Old 11-02-07, 05:22 PM
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Originally Posted by ibpooks View Post
> Did I get screwed by the HD saleperson?

You certainly wouldn't be the first. In my opinion, these stores are really irresponsible in passing off employees who are effectively minimum wage stock boys as "home improvement experts" in everything from wiring from roofing.
Well, HD requires people who work in the electrical dept of the store to be a licensed electrician so you can't blame the home center for the individuals ignorance. Also, often times a customer will snag any person wearing the orange vest and ask them questions they are not trained on. (I work at HD part time by the way).
 
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Old 11-02-07, 07:20 PM
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The guy I dealt with was definitely not a licensed Electrician. With the information I gave him about the project a licensed Electrician would not have sold me what he did.
 
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Old 11-02-07, 07:39 PM
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Mark,

Perhaps HD wants all their electrical employees to be electricians, and I suppose in an ideal world they would be. However, that is definitely NOT the case where I live.
 
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Old 11-02-07, 07:58 PM
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Originally Posted by racraft View Post
Mark,

Perhaps HD wants all their electrical employees to be electricians, and I suppose in an ideal world they would be. However, that is definitely NOT the case where I live.

I agree. I do not agree with alot of stuff HD does but you can't really expect a true licenced electrician to be working at a retailer either. 70% of the customers that come in know what they want and don't need to ask questions so there is no real need or demand to have such qualified people there. Most of the people I work with are 10 years younger then I, and I'm only 29. I've had to correct a few younger employees on proper ways of doing things.

Sorry to get off topic.
 
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Old 11-02-07, 09:46 PM
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OK just so that I get this right, for underground service through 1 1/2 inch conduit, from a 200A Main Service Panel running 85 feet to a Sub Panel.

For 100A service what size and type of alum wire and what size copper ground wire would I need? What size and type of copper wire and what size copper ground wire would I need?

For 125A service what size and type of alum wire and what size copper ground wire would I need? What size and type of copper wire and what size copper ground wire would I need?
 
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Old 11-05-07, 08:40 AM
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There are two ways of answering, and only your inspector can tell you which applies to the locality. All of these sizes apply to individual waterproof (THWN, XHHW, etc) conductors installed in the conduit, not cable assemblies.

If your jurisdiction allows table 310.15(b)(6) for subpanels:

100A copper: #4 THWN hots + neutral, #8 ground
100A alum: #2 hots + neutral, #6 ground
125A copper: #2 hots + neutral, #6 ground
125A alum: #1/0 hots + neutral, #4 ground

If your jurisdiction does not allow 310.15(b)(6) for subpanels:

100A copper: #3, #8
100A alum: #1, #6
125A copper: #1, #6
125A alum: #1/0 or #2/0, #4
 
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Old 11-05-07, 08:58 AM
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Originally Posted by HotinOKC View Post
I agree. I do not agree with alot of stuff HD does but you can't really expect a true licenced electrician to be working at a retailer either.
What really surprises me is that the corporate lawyers allow employees to give actual design advice in addition to the usual finding merchandise and sales type of help. I understand that there are certainly HD employees who are well trained or even licensed tradesmen working part-time, but most are neither trained nor qualified to give advice yet the company allows it to go on. I don't mean any offense to the individual HD employees as it is more of a systemic problem, but I would really rather hear "I don't know" or "I'm not allowed to give engineering advice" than to get a wrong answer.
 
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