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Old 03-14-2013, 03:29 PM   #1
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Electrical Wiring for Separate Garage


Hoping to get some advice on getting power run to a 20x20 garage I'm going to build in my back yard. I've had several electricians give me estimates that run the gamut from $700 to $2000. I'm trying to understand the wiring process, so I can make an informed decision as to how and who I want to do this job.

Currently have 100 amp service to my house (3 ton air conditioner on 25 amp breaker and dryer on 30 amp breaker). The outside meter and incoming power to the house is about 25 feet from the proposed slab for the garage. The inside breaker panel for the house (with 5 breaker slots remaining) is located in the basement, near the ceiling, just behind and below the outside meter.

I've looked at my power needs for the garage and two 110v 15 amp circuits and one 220v 15 amp circuit will suffice.

I've gotten the impression that two 15 amp breakers (one for each 110v circuit) and two 15 amp breakers (for one 220v circuit) need to be installed inside the house's inside breaker panel (total of four 15 amp breakers). Three multi-conductor a/c wires (connected to these four breakers inside the house breaker panel) will exit the inside house breaker panel (inside conduit), exiting the house straight down (still in conduit), and buried 24" underground (in conduit) 25 feet, all the way to the garage slab. At the garage slab, the conduit will exit straight up and into the garage to another breaker panel inside the garage. The three multi-conductor a/c wires will terminate inside the garage breaker panel to another two 15 amp breakers (one for each 110v circuit) and another two 15 amp breakers (for the one 220v circuit).

I believe this is what two electricians are proposing. However, one wants double the money to do the same thing. Another wants to change out my current 100 amp service in my house for 200 amp, then do the above, for about $2000. Yet another wants to skip the house altogether and install a new service meter directly to the garage. Sure, 200 amps and/or a separate meter would be nice, but I can't afford it, and don't need that much power.

Thoughts, opinions? Does the above proposal using the existing 100 amp service seem reasonable and safe? Thanks!

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Old 03-14-2013, 04:02 PM   #2
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Electrical Wiring for Separate Garage


I have done a few 100 amp sub panels to garage's from a 100 amp service where the people where more than happy with it and just knew they could not be running their big welder with the wife was baking in the electric oven and using every burner. But it also depends on the current condition of the service that is already there.

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Old 03-14-2013, 05:15 PM   #3
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Electrical Wiring for Separate Garage


You can only have one circuit run to the garage by code. Any electrician should know this.

A 50 amp sub panel should more than serve your needs.
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Old 03-14-2013, 05:57 PM   #4
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Electrical Wiring for Separate Garage


If that garage is only 25' from the meter, I personally would come off the load side of the meter and feed your garage via that route... Of course, this may or may not be easier, but what do you want with out looking at it.

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Old 03-14-2013, 11:28 PM   #5
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Electrical Wiring for Separate Garage


If you need two 15 amp 120 volt circuits for lights, tools, etc. and one 15 amp 240 volt circuit for large tools or an air conditioner then in reality you would run one 10-3 cable with ground (4 conductors in all). A double 30 amp breaker is in the main panel to feed it. When the cable gets to the garage it goes to a subpanel where you have two single 15 amp breakers for the 120 volt circuits and a double 15 amp breaker for the 240 volt circuit.

The suggestion was made to put in a 50 amp subpanel which I suppose would have 8 to 10 breaker slots giving you expansion room. For this use one 6-3 cable with ground to the garage, 50 amp breaker at the main panel. You would need a master switch at the garage which could be a top breaker in the subpanel or a separate double pole switch.

Before you start the project you need to do a load analysis for the garage and the whole house. (Refer to the NEC.) This may or may not reveal that you need a larger (amperes wise) service and also a larger main panel when you run the garage feed out of the main panel.
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Old 03-15-2013, 11:28 AM   #6
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Electrical Wiring for Separate Garage


Really appreciate everybody's inputs! The suggestion to run only one circuit (with both 110 phases) to the garage, instead of running three circuits separately from the house, is a great suggestion! I'm really surprised the two electricians I called didn't think of this. AllanJ, especially appreciate you taking the time to explain the details involved in actually running one circuit, thanks.

Can anybody suggest what kind of conduit (size and material) should be used to make the 25 ft. underground run from the house to the garage? They're suggesting burying the conduit 18-24". Is that a good depth?

Thanks again
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Old 03-15-2013, 01:49 PM   #7
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Electrical Wiring for Separate Garage


I would suggest going to 20 A breakers for the 120 V circuits. The cost delta between 14 g and 12 g wire is not so big and you may find you need the capacity in the future.
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Old 03-15-2013, 04:19 PM   #8
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Electrical Wiring for Separate Garage


Quote:
Originally Posted by HomeGuy2 View Post
Really appreciate everybody's inputs! The suggestion to run only one circuit (with both 110 phases) to the garage, instead of running three circuits separately from the house, is a great suggestion!
it's not a suggestion, it's a code requirement for your scenario....


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I'm really surprised the two electricians I called didn't think of this.
Maybe they are not really electricians?
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Old 03-15-2013, 04:20 PM   #9
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Electrical Wiring for Separate Garage


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I would suggest going to 20 A breakers for the 120 V circuits. The cost delta between 14 g and 12 g wire is not so big and you may find you need the capacity in the future.
The little added capacity isn't really worth the material in some cases...
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Old 03-15-2013, 09:30 PM   #10
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Electrical Wiring for Separate Garage


Then why are 20 A circuits required per code in kitchens and bathrooms?
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Old 03-15-2013, 09:33 PM   #11
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Electrical Wiring for Separate Garage


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Then why are 20 A circuits required per code in kitchens and bathrooms?
Because of coffee pots, toasters, microwave, and hairdryers!
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Old 03-15-2013, 10:50 PM   #12
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Electrical Wiring for Separate Garage


And circular saws and heat guns and who knows what... The OP never said what he intends to do out there...

No intent to create a ruckus, but IMHO I'd rather have the capacity built in than regret it later.

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