Yet another wire gauge question

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  #1  
Old 05-16-07, 12:57 PM
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Yet another wire gauge question

I want to run power underground from the house to a small garage.
I don't need 220 volts. The heaviest load on this circuit would be a power tool such as a circular saw. The distance is about 150 feet. What size and type of wire do I need? What size and type of breaker should I use?

Thanks
 
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  #2  
Old 05-16-07, 01:13 PM
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You can run a single 20A circuit to the outbuilding. For a 150' distance, you'll want to use #10/2g copper UF-B "waterproof underground feeder" cable and a single pole 20A breaker. If you add GFCI protection before the wire leaves the house, the cable only needs to be buried 12"; otherwise 24" deep. The receptacles in the garage should have GFCI protection in either case.

A second option would be to install a multi-wire circuit. This adds about 30% to the wire cost, but allows you twice the available power at the garage and the limited use of 240V tools. If you're interested in this option, please post back for details.
 
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Old 05-16-07, 01:39 PM
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Ben-- Not to contradict you but last I knew I thought it was 24" no matter what unless you use PVC then it drops to 18", and Rigid conduit is 6-8" below... if it's a code I'm not firmiliar then please let me know for future reference.
 
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Old 05-16-07, 01:40 PM
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I either recommend:

Conduit and a 120 volt circuit using THWN wires, so you can upgrade to a multi-wire circuit at any time.

OR

UF-B cable and a multi-wire circuit to start with.

Use 10 gage wire (so that means 10-3 UF-B or 10 gage THWN.
 
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Old 05-16-07, 01:52 PM
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> I thought it was 24" no matter what unless you use PVC then it drops to 18"

Table 300.5 "Minimum Cover Requirements"

Column 4 -- "Residential Branch Circuits Rated 120V or Less With GFCI Protection and Maximum Overcurrent Protection of 20A"

"All other locations" = 12 in.

See also, note 4 of that table.
 
  #6  
Old 05-16-07, 02:12 PM
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Just to clarify, Table 300.5 (to which Ben refers) has five columns and seven rows covering 35 different situations, each of which has its own requirements for burial depth. Then there are five notes of exceptions and conditions.

gsharpe, you have a lot of different options depending on whether you want the cheap solution of the deluxe solution. Which you choose might depend on what your budget looks like, how much you might be using this garage, and what enhancements you can foresee for the future.
 
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Old 05-16-07, 03:10 PM
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Call your local town's inspector and ask what they want for your situation for burial depth and any conduit requirements. That is what is going to matter in the end.
 
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Old 05-16-07, 03:42 PM
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Thanks Ben & John.
 
  #9  
Old 05-17-07, 05:47 AM
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RE: Yet another wire gauge question

I like the cheap option. 10/2g UB-F with the single pole 20A GFCI breaker in the house panel.

Questions:
Upon entry into the garage, do I need a second breaker?
Can I step down to 12/2g wire iinsde the garage with out one?
 
  #10  
Old 05-17-07, 06:51 AM
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I think you are making a mistake that you will regret later on. A few dollars more spent now is good insurance.

You need a disconnect in the garage. This can be a simple toggle switch.

You can switch to 12/2 in the garage after the disconnect. Actually, you can switch to 12/2 at any point, but the disconnect make a convenient place to do so.
 
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Old 05-17-07, 07:14 AM
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If you want the even cheaper option, you can use 12/2 UF-B underground too. The voltage drop will be a little out of norm during periods of high usage, but it doesn't sound like you're going to have any periods of high usage, at least not with your current plans.

And using a GFCI receptacle will be a lot cheaper than using a GFCI breaker.
 
  #12  
Old 05-17-07, 07:21 AM
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RE: Yet another wire gauge question

I agree with the regrets part and thank you for your concerns.
I am afraid that trenching any deeper than 12" is going to get $$$$.
Just below the surface is a 4 foot thick layer of sand rock. I know it is
there from having excavated for the sewage system. If I can lay conduit
in a 12" trench and upgrade to 220V I will. What are my options?

The garage is just for storage, albeit I cannot predict the future.

Thanks again.
 
  #13  
Old 05-17-07, 10:00 AM
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Unfortunately, the only ways you can install a 240V feeder in a 12" trench is to use rigid or intermediate metal threaded conduit; or to pour 2" of concrete over PVC conduit. This would be more expensive and a lot of extra work for your project.

You could ask the electrical inspector if he will allow column 4 of table 300.5 to apply to multi-wire circuits for 12" burial depth. In this case, you could use 10/3 UF-B cable and a 2-pole GFCI breaker. The breaker alone adds about $100, but you will have twice the available power at the outbuilding.

The 10/2g UF-B with a 20A GFCI breaker or receptacle is okay in a 12" trench and will be the cheapest and easiest option.
 
  #14  
Old 05-30-07, 06:30 AM
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Smile Smooth as silk

The job is done.
From the panel:
20 AMP breaker.
12-2/g UF to 20 AMP GFCI recepticle.
12-2/g UF into 3/4 PVC conduit through exterior basement wall.
12-2/g UF buried 16" 150' to garage.
12-2/g UF into 3/4 PVC conduit riser and through garage exterior wall.
12-2/g UF into 4" work box - 20 AMP single pole switch and recepticle.
branch to lights and recepticles.

They only tough part was running the trenching machine.

Thanks for the help guys.

gsharpe
 
  #15  
Old 05-30-07, 06:46 AM
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Good job. Congratulations. Sounds like you did things perfectly!

Note that you did, however, take the cheap solution. That's just fine, but remember in the future that if you need more power, you'll need to abandon everything you just did and start over with a different solution. I hope that day never comes.
 
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