electricity to a new garage


Old 09-16-04, 09:41 PM
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electricity to a new garage

I built a new garage as follows:

720 square feet
Uninsulated/not heated
Shop area where a table saw, miter saw, shop vac, etc... will be run
75 feet from the main service panel of the house

Future plans:
I may insulate and heat with a wood stove someday.
It is very possible that I may be occasionally running a compressor.
Welding is unlikely, but you never know...

My plan was to run #4 UF cable, buried 24", to a 60 amp subpanel in the garage. I intended on trenching in an equipment grounding conductor with the UF. Is the #4 cable size appropriate, or is it overkill? (Would #6 be OK?) What type of wire would I want to use for the EGC? What type of grounding system do I need at the garage?

A friend of mine is trying to convince me to go with a 100 amp subpanel instead. Is this more than I need? What type of wire would I need to use instead if I were to make this change?

I really appreciate any help that some of you can offer....
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Old 09-17-04, 07:37 AM
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#4 is more than you need for 60-amps of 240-volts over 75 feet. #6 would be good enough.

Doesn't the UF you are going to use already have a grounding wire in the cable? Don't run another EGC.

I would go to 100 amps only if the welder is a realistic possibility, or if you're willing to go to the extra cost and effort to allow for the possibility. You'd need #2 copper for that (or #3 if you run individual wires in conduit and the terminations at each end are marked as 75-degree terminations).
Old 09-18-04, 07:36 AM
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My old shop had 60a service and I ran a 110v welder and a 220v compressor as well as lights, tools etc. It never was a problem. I went with 100a this time so I could go with air conditioning in the future. Like that's ever gonna happen...
Old 09-19-04, 03:12 PM
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Question please bare with me, more and more questions...

I was ready to go with #6 UF for 60 amp service. And John is right, the 4th wire (ground) is already in the UF cable.

Just for curiosity, I decided to price what the 100 amp service would cost. There is a signicant difference in breaker prices. However, when it comes to running the 75 feet of wire itself, I was shocked to find that I could run #2 URD aluminum much cheaper than the 6-gauage UF. Now for all the new questions. I appreciate any help that some of you more experienced ones can give this novice!

Is #2 aluminum suitable for 100 amps? I know John said #2 copper would be, but with aluminum would I need to jump up in size further?

The aluminum URD I was looking at was rated 2/2/4. I would assume this is #2 on the lives and #4 on the neutral. Is this still OK for 100 amps?

What type/size of wire should I run with the URD as a ground? Aluminum or copper? #6?

Please verify if the following information that I have researched is indeed correct:

Direct burial requires a 24" trench.

When running 4 wires to the sub at the garage, I will need one grounding rod connected to my subpanel with #6 copper.

I must keep the ground and neutral isolated in the sub.

The subpanel should not be a MLO type (main lug only).

Thanks for any help any of you can offer!
Old 09-19-04, 04:42 PM
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#2 aluminum is not allowed for a 100 amp subpanel by the NEC. However, it is allowed by a number of inspectors. So the only way to know is to ask your inspector. In my opinion, copper is worth the extra cost, especially if you're not familiar with the safe use of aluminum. I know that others will differ.

Whether you need one grounding rod or two is again up to your inspector. The inspector takes into account soil conditions in your area.

Whether or not you can use an MLO depends on how many circuits you have.
Old 10-01-04, 12:19 PM
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I talked to my inspector, and #2 aluminum is acceptable for him. I will be using two ground rods. I have a friend who is experienced running aluminum URD, so with his advice I think everything will work out OK.

I do have a few more questions once power is supplied to the garage. I plan on running 20 amp breakers/#12 romex for my outlets and lights. I will use 20 amp GFI outlets at the beginning of the receptacle circuits.
- Would you recommend 15 or 20 amp plugs downstream from the GFI's?
- How many GFI-protected (but not GFI themselves) can be run afterward. Does the chance of tripping the GFI increase as more are added?

I plan on leaving the garage unfinished for many years (it may neverr be sheetrocked or insulated).
- Should I put all my boxes flush with the studs?
- I would assume any wire along the ceiling (which will be minimal) would be best run on the sides of the truss 2x4's. If any must run across the trusses, would stapling to the side of a runner nailed to the trusses be the best bet?
- From what I understand, regular romex is acceptable in an unfinished garage. What precautions should I take as I run my wire to minimize the chances of any damage?

I really appreciate the help...
Old 10-01-04, 12:30 PM
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I would use 15 amp receptacles, unless you have a 20 amp device that you plan on using. You may use as many as you want on a circuit and it does not change the GFCI protection on the circuit.

If you put the boxes flush with the studs you can always move them later on if you need to, or add extensions (if you use the right type of boxes).

Yes, stapling to a runner is okay in the ceiling.

You may use NM type cable in the unfinished garage, as long as the cable is protected. "Protected" is a subjective term. The inspector will decide if the cable is protected or not. Some people use conduit for protection, other hide the cable behind a strip of wood.
Old 10-01-04, 06:54 PM
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The MLO is fine unless you install more than 6 branch circuits, then you will need a main breaker disconnect in the sub panel. I would seriously look at the probability you are ever going to need 100 amps. I suppose that welder could get you up there depending on what kind of welder. An arc welder is pretty heavy load but wire welders arent in the majority of cases. Like John I like copper as Al has termination issues. Lots of money is wasted by overkill. Anyway guess the question is if you use Al you can go with 100 amp panel at same or better cost. Also since you are feeding from your dwellings main panel that demand load for the garage goes against the service rating of that main panel. So you need to be sure if you start putting 60 or 70 amps to the garage you dont exceed the demand load for your home main panel. Could cause you to indure the expense of a main service upgrade.
Old 10-06-04, 09:35 AM
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OK, I'm doing a similar project, just a little bit larger garage. It's about 60 Ft from Garage to House.

Garage Door Openers: Looking to run .75" conduit for that & run a 4 pair CAT 5 wire to run the 2 door openers. I would then split the pairs and attach push button controllers at the house end.

3-way switch for garage lights in house: Running another .75" conduit for that. No other wires in there.

Questions :
1 Could I run another CAT 5 cable through the pipe with garage door opener wire for future communications needed, or do they need to be keep seperate ? not sure of the garage door opener voltage, but figure it's got to be around 24 volts.
Old 10-06-04, 11:27 AM
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It's okay to run all the low-voltage wire together.
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