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Old 05-13-2009, 12:17 PM   #1
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Wiring Main-Breaker Box in Detached Garage


Hello Folks!

Before everyone tells me "just call an electrician!"... I want to let you know that IS the plan, haha. However, being one of those people who can't live without knowing how something should work, I need some help understanding exactly how the wiring for my detached garage should work. Furthermore, I'd like to thank everyone in advance for the advice and knowledge you share!

So without further delay, here's the skinny on my situation. I bought a house a year ago and had to ahve the entire house's electrical gutted and replaced. I've got a detached garage (man-shed) approx 40 feet off the back of my house. When the electrician was wiring the house, he told me he could put drops in the garage for an extra 1000 dollars yadda yadda. Being that I just dropped all my money on a house and getting it rewired, I decided to hold off but had a wire ran out there for when I was ready to do so.

As of now, there is a double pole 100 amp breaker on my houses main breaker for "shed". The wire the electrician ran to the garage is (I believe) a #4 Copper 3-wire (Black, Red, and a bare copper). The Black and Red are connected to the "shed" breaker in the main panel, with the bare wire lost somewhere in a mix of wires.

Into the shed, the business end of the wires were capped and ran through condiuit into my shed, so all that's missing is a box to bring it all together. My plan is to have a main breaker in the shed (NOT a standard sub-panel, that way I don't have to run back and forward when I want to add additional circuits)

My questions:
If there are two hot wires (black/red) to carry the 240V to the shed, would that make the bare copper wire the return? If the bare copper is the return, it is my understanding that a grounding rod and wire will be needed at the shed.

If you run a 3 wire, must you bond the ground and nuetral in the panel?

Was the electrician wrong for not using a 4-wire in order to have ground, return and feeds all in one wire?

If the bare copper wire is intended for grounding, would it be acceptable to use it as a return, with the addition of a ground rod & wire?


I appologize for anything that is unclear. I'm sure you all will have just as many if not more questions in return, so I will do my best to "paint the picture" of what's going on. Also, I've attached a drawing, b/c pictures make things easier!

Thanks Again
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Old 05-13-2009, 04:22 PM   #2
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Wiring Main-Breaker Box in Detached Garage


I beleive that he should have run a #4/4 wire. that should be red/black/white/ground. and to my knowledge a bare ground wire should never be used for a liv e load only grounding. Now for me, and its probably overkill. and since i have the same set up at my house to my garage. in addition to the grounding at the main box, i also have a ground at the sub panel in the garage. im sure there will be other folks who state me as wrong, but in all my research ive never heard of a bare wire being anything but ground.

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Old 05-14-2009, 12:00 PM   #3
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Wiring Main-Breaker Box in Detached Garage


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Originally Posted by wstribl View Post
Hello Folks!My questions:

If there are two hot wires (black/red) to carry the 240V to the shed, would that make the bare copper wire the return? If the bare copper is the return, it is my understanding that a grounding rod and wire will be needed at the shed.

If you run a 3 wire, must you bond the ground and nuetral in the panel?

Was the electrician wrong for not using a 4-wire in order to have ground, return and feeds all in one wire?

If the bare copper wire is intended for grounding, would it be acceptable to use it as a return, with the addition of a ground rod & wire?


I appologize for anything that is unclear. I'm sure you all will have just as many if not more questions in return, so I will do my best to "paint the picture" of what's going on. Also, I've attached a drawing, b/c pictures make things easier!

Thanks Again
No. The bare copper wire is the ground. It carries no current other than fault current. This wire connects to the sub panel grounding terminal strip and the grounding rods. Yes, you need rods.

No. Never bond neutral and ground in sub panels or anywhere else other than the main service. See your exception below*.

Yes & No. The electrician should have run 4 wires if this was done recently. 3 wire feeders were legal before the 2008 code came out. 3 wire feeders are now banned. Depends on your local jurisdiction and what code cycle they follow.

You use the word return more than once in your post. You mean the neutral. The neutral carries the unbalanced current of the other two conductors. This conductor must be insulated. Bare conductors are not designed as current carrying conductors, only fault paths.

*Since you only have a 3 wire feeder of course you must bond the neutral and ground to the rods at the garage panel. You are basically building a new service. You CANNOT have any other metalic paths from the house to the garage. That includes phone lines, water lines ect....This is very important.
You must use a main breaker panel or install a disconnect at any unattached structure.

Sounds like all the hard work has been done for you. When you apply for a permit and get an inspection would be the worst time to find out you needed a 4 wire feeder. Find out now, before you do anything.
Help is here. Just let us know.

Ps...You need #3 copper for 100 amps. You may have to use a smaller breaker. Double check the wire size.

Last edited by J. V.; 05-14-2009 at 12:13 PM.
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Old 05-14-2009, 12:09 PM   #4
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Wiring Main-Breaker Box in Detached Garage


Quote:
Was the electrician wrong for not using a 4-wire in order to have ground, return and feeds all in one wire ?
No, you were wrong

An electrician would not have made such a blunder.

Start digging......... and install conduit this time.
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Old 05-14-2009, 12:29 PM   #5
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Wiring Main-Breaker Box in Detached Garage


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An electrician would not have made such a blunder.
Do you really believe that?
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Old 05-14-2009, 12:32 PM   #6
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Wiring Main-Breaker Box in Detached Garage


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Do you really believe that?
Of course he does. He just didn't add the qualifier: real before electrician. A so-called electrician might do it that way, but a real electrician wouldn't.
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Old 05-14-2009, 12:45 PM   #7
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Of course he does. He just didn't add the qualifier: real before electrician. A so-called electrician might do it that way, but a real electrician wouldn't.
That's more believable.

Sorry I had this image come to mind of a home depot sales person doing this electrical install telling the client that "theres no reason to spend the extra money on 4 wire service when all you need is 3 wires" (this as far as I know did not actually happen).

I could see where an electrician might ask questions about if they will ever need anything more than just power out at the detached building and then coming to the solution that only 3 wire service is needed.

The fact that the op bought the house a year ago and had this done, it really should have been a 4 wire, but I guess it depends how early on this install was done and how up to date the "electrician" was on the new codes.
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Old 05-14-2009, 12:48 PM   #8
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Wiring Main-Breaker Box in Detached Garage


Of course I believe it.

I'm not that bright and I KNOW that I learned the basics in less than a week.

A 120/240 circuit is the very first day of electrical 101
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Old 05-11-2013, 11:57 AM   #9
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Wiring Main-Breaker Box in Detached Garage


jv you stated that 100 amp in detached garage needed # 3 COPPER ARE YOU SURE IT IS NOT TO BE #4 COPPER? Table 3603.1 "service conductor and GEC sizing"
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Old 05-11-2013, 12:15 PM   #10
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Guys and OP....

Don't know how much digging is involved and what OP's demand is going to be in the "shed",.... but how about just sending one leg out to the shed???

Peter

Edit: And buying some white tape
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Old 05-11-2013, 12:34 PM   #11
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Wiring Main-Breaker Box in Detached Garage


Quote:
Originally Posted by J. V. View Post

*Since you only have a 3 wire feeder of course you must bond the neutral and ground to the rods at the garage panel. You are basically building a new service. You CANNOT have any other metalic paths from the house to the garage. That includes phone lines, water lines ect....This is very important.
You must use a main breaker panel or install a disconnect at any unattached structure.
JV... Sorry I'm confused.... Doesn't the OP just have a 2 wire feeder and how can he build a new service with just two wire.

Thanks

Peter
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Old 05-11-2013, 01:07 PM   #12
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Originally Posted by mr leak View Post
jv you stated that 100 amp in detached garage needed # 3 COPPER ARE YOU SURE IT IS NOT TO BE #4 COPPER? Table 3603.1 "service conductor and GEC sizing"
You want to try that Table# again?
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Old 05-11-2013, 01:17 PM   #13
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This thread is almost 4 years old.
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Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.
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Old 05-11-2013, 01:22 PM   #14
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This thread is almost 4 years old.
Wow.... wonder how that happened.

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Old 05-11-2013, 01:24 PM   #15
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Quote:
Originally Posted by Jim Port View Post
This thread is almost 4 years old.

In before Close

Quote:
Originally Posted by [B
mr leak][/B]
jv you stated that 100 amp in detached garage needed # 3 COPPER ARE YOU SURE IT IS NOT TO BE #4 COPPER? Table 3603.1 "service conductor and GEC sizing"
Quote:
Originally Posted by sirsparks
You want to try that Table# again?
Table 310.16 #3 CU for 100A

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