Power to workshop/garage


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Old 08-17-04, 09:50 PM
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Power to workshop/garage

I need to run electrical service to my workshop. It's about 85 ft from pedestal. I'll be using a 100 amp breaker at pedestal and need to know what kind of cable to use. Is there a direct burial cable that will suffice? If so what exactly is it called and what is the proper guage? Or will I have to run the four wires (2 hots, one common and ground) through conduit? If so what guage of each will I need? It is in a remote area and will not be inspected, but I want it to be safe of course.
Thanks, Jim
 
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Old 08-18-04, 08:11 PM
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Still looking for help

Anyone? any advice would be appreciated.
 
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Old 08-18-04, 09:02 PM
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The direct burial cable is UF (Underground Feeder). You'd run either #1 copper or 1/0 aluminum. UF needs to be buried at least 24" deep.

If you want to run conduit, you'd pull #3 THWN (copper). Non-metallic conduit needs to be buried at least 18" deep.
 
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Old 08-19-04, 11:15 AM
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I have 100 amps in my shop. I had to run about 60 feet and used 2-2-2-4 direct bury aluminum. The local suppliers call it "trailer feed". I buried it about 30 inches and it met code for Mid. Ga.
The stuff is expensive at about $1.35/ft so make sure you measure well
you buy enough.
The 2's go to the main breaker and neutral bar in the shop and the 4 goes to the ground bar which is isolated from the neutral and bonded to the box. The 4 is tied into the neutral at the house which is also tied to the ground rod. This saved me from driving a ground rod at the shop.
I hope this isn't confusing because it sure confused the heck out of me while figuring it out.
 
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Old 08-19-04, 08:19 PM
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Where can I find it?

Thanks for the replies
No one seems to carry buriable cable the size I need. One supplier has all single strand at .72 a foot. 85 feet times 4 wires, times .72 = a lot of money.
Home Depot has wire a bit cheaper but not UF so I'll have to add the expense and trouble of conduit. I might as well order your 2-2-2-4 "trailer feed" from Georgia. At twice the price it would be cheaper than any solution I'm finding here.
 
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Old 08-19-04, 08:33 PM
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I would opt for conduit in any case. It is a safer job and the wiring can be replaced in case of a problem.
Just so you know. I don't know where Hoffman got the info for his project but a ground rod is ALWAYS needed for a separate structure.
Here is some very good reading: http://www.homewiringandmore.com/hom...detgarage.html
 
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Old 08-19-04, 08:53 PM
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While I have your ear Speedy, what do you think? #3 THWN copper for the two hots and common and something smaller for the ground? What size conduit?
 
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Old 08-19-04, 09:25 PM
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Run two #3 and, if you like, you can undersize the neutral to #1. Or just run 3- #3 and a #8 ground.
Run this in 1 1/4" or 1" pvc conduit using schedule 80 where the conduit is above ground.
Run a #6 cu from the garage panel to a ground rod.
Keep the grounds and neutrals separate in the panel. You may need to buy a separate ground bar. You can go without the ground wire in the conduit if you have NO OTHER metallic paths to the garage, such as phone, cable, water, gas, etc.. In this case you treat the panel in the garage as if it were a main panel. Keeping the neutral bonded to the panel box using the provided bonding method.
In any case you do need the ground rod.
 
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Old 08-20-04, 02:57 PM
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I have phone/cable/water to the shop. The local inspector said it was safe to run it the way I have it. So should I drop a ground rod out at the shop? I originally planned on it and even bought the rod/fittings but the inspector said don't bother.
 
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Old 08-20-04, 03:07 PM
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Every detached structure should have a ground rod if it has its own panel. If your inspector says it's not necessary, then it's only for you, not for him. It's cheap insurance.
 
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Old 08-20-04, 03:22 PM
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Wow. I had him look at it and give me some pointers while I was doing it and then it had to be inspected before the power company put the meter back in. He's the one that told me to run it without a rod at the shop. I just thought that any big panel with multiple loads had to have it's own rod and had bought one...
I think I'll drive that ground this weekend while the dirt is soft.
What do you do when you don't want to do stuff half-ass and the city inspector tells you to do it that way?
 
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Old 08-20-04, 06:52 PM
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If the inspector tells you to do bad work, don't bother telling him he's wrong, he won't believe you . Just go ahead and do it right, you will then have the NEC on your side, if he says "do it this way"(wrong), and you do, what will you do if the other city inspector comes for your final inspection? (besides fail).

On the other hand, if inspector 1 tells you to do something wrong, and you don't, even if same inspector comes for final, he probably won't remember telling you, and if he does, just POLITELY point out that you decided, since you already had the materials, you would put them to use. If he fails you for spite, appeal it.
 
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Old 08-20-04, 09:37 PM
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Well gang, I did find the 2-2-2-4 trailer feed and it looks like the easiest, most economical option. It says it's rated for 100amps. Other than the ground rod, are there any special considerations I need to make as it is an all metal building?
 
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Old 08-23-04, 11:51 AM
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I'm just wondering if there are any special considerations with an all metal building.
I believe I'll run the 2-2-2-4 aluminum trailer feed as it is rated for 100amps, and it is less expensive and easier than my other options.
 
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Old 08-23-04, 03:30 PM
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More of my "expert" advice...
My last house had one of those Steelmaster buildings like you see in the back of Popular Mechanics magazines. It was a real pain wiring it up because I had to string chains to hang shop lights from and all the wiring had to be in conduit. I used the greenfield type of flexible stuff plus you have to have all the little connectors. There may be an easier way but that's how I did it. Lots of work fastening the conduit/boxes to the walls.
What type of steel building do you have?
 
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Old 08-24-04, 10:29 AM
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It's a modular steel building manufactured by Armco, bought used in pieces.
You don't have to isolate the box or the conduit from the metal walls do you?
I hope I can just screw em in.
 
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Old 08-25-04, 08:28 AM
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Sounds like my old shop. When the slab was poured I had conduit laid in it for the electrical. I mounted a piece of plywood to the wall for the breaker panel and used metal outlet boxes that were fastened using some of the zillions of bolts that held the building together. For the wiring I used flexible metal conduit that comes with the wire in it. Don't forget those little red insulator deals that keep the wires from rubbing against the conduit. I did and had to re-do most of it to install them.
I originally planned on running outlets to all sides of the shop but got tired of bolting conduit and only had outlets on one wall...
If you scan my webpage you can see some of how I rigged it up.
http://motorhead.iwarp.com
Good luck. All of my work met code but I have learned recently that some inspectors can give you bad advice.
 
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Old 08-25-04, 09:39 AM
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Please note that 2ga aluminium is not rated for use as a 100A feeder.

If you look at NEC table 310.16, you will see that 2ga aluminium is only rated for 90A, and that is if you are certain to use 75C terminations.

The use of 2ga wire for feeders to subpanels is a very common error, because NEC table 310.15 permits the use of 2ga aluminium for a '100A service' to a dwelling. If you had a home with a 100A main breaker, then you could use 2ga aluminium as the feed to the home.

This does not mean that you can use 2ga aluminium to carry 100A of current to a home. Instead it means that if you follow all of the load calculations for a home, and the result of these calculations say that you need a circuit rated 100A, you can feed this home with a 90A conductor and protect it with a 100A breaker.

The electric code permits similar 'oversizing' of the breaker relative to the conductors in other specific instances, in particular welders and electric motors, where you might see a 50A breaker protecting conductors rated 25A. This is permitted in _specific_ situations where the characteristics of the load in normal operation will protect the conductors from thermal overload, and the breaker is sufficient to protect the conductors during a failure.

There is no exception for a garage workshop, other than the 'round up' rule, which will let you use the next larger 'standard' breaker on a wire; if your conductors have an ampacity of 95A, you can use a 100A breaker.

I personally would not lose sleep over 2-2-2-4 Al being used as a feeder to a home workshop with a 100A breaker, since my gut feeling is that the load characteristics of a home workshop are similar to that of a dwelling, but you should be aware that this is a code violation.

-Jon

There are other situations
 

Last edited by winnie; 08-25-04 at 01:24 PM.
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Old 08-25-04, 12:54 PM
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Jon, my reading of the code agrees with you. Nevertheless, #2 aluminum is the standard 100-amp feeder in many areas, and many inspectors allow it.
 
 

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