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Old 01-03-2011, 08:05 PM
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Best way to supply power from the house to the garage.

I am building a garage in the back yard and want to supply the garage with electricity by running wire underground from the service panel in the house to a new service panel in the garage. Will have Square D service panels in both locations. Was planning to use UF cable inside PVC conduit.

I have a 200 amp service panel in the house with 10 slots available to use.

The distance between the service panel in the house and the service panel in the garage is 75 feet.

The electrical requirements in the garage are 180 amps -25030 watts, when I add up all the 120 and 240 outlets that I want. Can supply a breakdown of the circuits if needed.

Is it possible to do this? If not what is the max amps - watts I can run out to the garage?

What is the best way to accomplish this as far as the circuit breaker in the house for the garage, and size and type of wire going to the garage?

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Old 01-03-2011, 08:15 PM
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Not gonna need no 200 amp service back there unless you are putting in a HUGE AC unit and a couple of pizza ovens.

When in Phx AZ I just ran a 100 amp back to the garage.
100 Amp breaker in the main house panel, to a breaker box in the garage
with about 10 slots.

About all you will need is a 50 amp circuit for a welder, a couple of lighting circuits, 30 amp for a air compressor, and maybe 3-4 20 amp circuits for outlets.

Not very likely you will be using all of your outlets, Air compressor, and welder at the same time.

Also had to drive a ground rod into the ground near the breaker box in the garage, and the main box and the breaker box ground wires were attached to it.
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Old 01-03-2011, 09:12 PM
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Hot Rod, is your garage plumbed for water?
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Old 01-03-2011, 10:14 PM
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The reason I ask about the plumbing is that is what will determine how you need to ground the new panel. If you have metallic plumbing out to the garage, you will have to have a grounding conductor along with your hots and neutral.

In that case, you would be wasting money to install a ground rod, when you could just make sure you don't bond the ground and neutral busses together in the new panel.

If you don't have metallic plumbing, you can just run the hots and neutral out to the new panel, bond the neutral and ground together at the new panel, and install a ground rod (a lot of jurisdictions will require two).

You will need a main circuit breaker in the new panel either way.

Of course, your local AHJ will have the final word.
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Old 01-03-2011, 11:36 PM
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No water in the new garage

No water in the new garage. Thanks for the info.
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Old 01-03-2011, 11:56 PM
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Wire and breaker required for this load?

What size wire do I need to run from the house to the garage?

What size breaker goes on the main house panel?

To give you a better idea of the load requirement in the garage, here are the particulars for the 24 X 38 garage.

22 wall outlets 20 amp 120 volt (2 circuits)

20 80 watt light fixtures inside 120 volt 20 amp (1 circuit)

4 100 watt light fixtures outside 120 volt

1 30 amp circuit for the heat and air unit 220 volt

1 40 amp circuit for the welder 220 volt (recommended by Lincoln)

1 30 amp circuit for the compressor 220 volt

1 20 amp 120 volt dedicated circuit for a small refrigerator (optional)
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Old 01-04-2011, 05:59 AM
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better have a whole service installed...or buy good fire insurance.
Seriously your wiring needs to be heavy enough to handle the sum of the equiptment you have ,regardless if it is all running at the same time or not.
Running a 100 or 150 amp subpanel from a 200 main is definetly not going to be code.
And if you have added all your equiptment load together in amps , the wire you need to use will have to be big enough to handle it. Then the fact you are going 75 feet to the garage means you need to go up one size.
Dont fool with too light of wiring, it will burn out your equiptment and burn down your new man cave.
You will need probably a 2 awg wire to hook it up and at 75 feet to be safe. There isnt anywhere to hook that inside the existing panel.
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Old 01-04-2011, 06:16 AM
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Several years ago I had the same .....the City installed a separate service to my garage for free. All I had to do is have a box and a licensed Electrician install from service to box to code.
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Old 01-04-2011, 07:05 AM
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My garage currently has a 60 amp coming underground from the house. I have a 220 volt 5 hp 2 stage compressor, a 5000 watt electric heater, around 12-15 outlets, and 8 8' high output fluorescent lights with 2 110 watt bulbs in each fixture. I haven't had any issues so far. In these winter months I have been running the heater, the compressor, and the lights at the same time. I'm not an electrician by any means, but 60 amps is running more than I thought it would when I bought the place.
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Old 01-04-2011, 07:20 AM
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Hotrod,

as Fergusonic mentioned, of course I recommend a licensed electrician do it. Depending on where you live, it might be required by law, or at least he has to pull the permit, even if you do the work.

As far as the load, to me it sounds like you will be fine with a 100A feed to the garage, possibly a 125A. This is perfectly code compliant, as long as your main house panel will hold a 125A branch circuit breaker (many won't).

I'm not sure if you can get UF cable in more than 95A, so you could possibly find a 90A circuit breaker for the house panel. Either that or go with THWN wire. You don't need to size the wiring for everything at once...the circuit breaker will protect the wiring. However, the higher the main circuit breaker is, the more chance you stand of tripping out your whole house should you get any kind of short anywhere. More of an annoyance than anything.

Make sure to calculate your voltage drop from the main panel to the garage panel. There are many calculators on line. You want to keep the drop under 2%.
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Old 01-04-2011, 09:23 AM
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i have a 20x24 garage i ran a 110 wire from my house in pvc to the garage for 7 plugs 2 light switches and 4 lights and i ran another 220 wire in pvc for my compressor 1 15 amp breaker for the 110 and a double 30 amp breaker for the compressor it never pops and it dont dim unless i use my welder and the light in the garage dont dim but the lights in the house do
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Old 01-04-2011, 09:29 AM
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Hey mafia,

That sort of thing is done all the time, but it is a major no-no code-wise. If you ever try to sell the house, you are going to get your bells in a sling with the local inspector.
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Old 01-04-2011, 01:16 PM
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hotrod
some of the posts above are incorrect. unless things have changed, you should be able to do all the work yourself, check with your building dept. unless your running a commercial shop a 100 amp panel will be sufficient. if you have correctly sized conductors and circuit breakers for that conductor; fire/overloading are not an issue.

UF-B cable is not rated above 95 amps.

if you run out of your existing panel, then your garage panel is considered a sub-panel and will require a 4 conductors, 2 hots, ground and a neutral. size of these conductors is dependent on how far from house to barn. #2 THWN is good for 115 amps, if your run is 50 ft you could use #2. any longer and i would step up to #1 THWN (130A). THWN will require the use of conduit and must be buried a minimum of 24 inches deep. use pvc conduit, it's cheap and easy. minimize your bends, 360 is max but it will be a bear to get in there. drive an 8 ft ground rod and use a solid #6 to ground the panel.

code allows you to run a 2nd panel off your meter base to an out building, this was added 20 yrs ago just for your situation. as a panel you can run 3 conductors; 2 hots and 1 grounding conductor. same wire/conduit constraints as above. if you are comfortable working in the meter base this is your best option. if not find an electrician to do the actual hookup.

run everything by your building dept, walk in there with a plan on paper, a simp[le pencil sketch may work. if your up front about it, they can be your best friend. if you try to sneak anything past them, they can be your worst enemy.

that said: my barn is 200 ft from my panel. it was originally a horse barn and only need lights and 110 circuits, it has 1- 30 amp, 220 volt, 3 wire circuit (#10) from my house panel, feeding the barn. when it was installed 40 yrs ago this was legal. i have a 100 amp, 12 circuit panel attached to this 30 amp circuit. i replaced the 100 amp breaker with a 30 amp breaker. the panel has 1- 20A 220V and 5- 20A 110V breakers in the panel. i have a wood shop and car shop out there; gas furnace, 2 table saws, lathe, welder, 5 hp compressor and 15- 4 ft fluorescent lights. is it safe? yes. wire is sized for breakers. does it work? yes. you can't start the table saw when the compressor is running and the lights dim when any big motor is started. do i need to replace it? yes, but it's a $1000 project that i can live without for now.

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Old 01-04-2011, 01:51 PM
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Ogre...the ground rod is not needed unless the neutral and the ground are bonded inside the garage panel, which is specifically forbidden by code if the feeder to the panel has a grounding conductor. The house panel already has the neutral and ground busses bonded together. They can't be bonded in two places.

So you either run an ungrounded feeder to the panel, establish a ground out at the garage with a rod, or you run grounded to the panel, with no ground rod. There is an exception in the NEC for running without a ground to a sub-panel outside of the house, i.e., in a garage.

Some states allow him to do the work himself, some don't...better to be safe than sorry.
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Old 01-04-2011, 02:14 PM
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According to the NEC, you are installing a sub-panel in the garage. For combined 110/220 service, you MUST use four wires to the sub-panel - two hot wires, neutral, and ground. At the sub-panel, you MUST install a separate ground bar from the neutral bar. The neutral must be isolated from the panel. The ground bar must be connected to the panel with a bonding screw and to a ground rod at the garage. As noted, UF is not what you want, you want USE (underground service entrance) cable. Neither UF nor USE is supposed to be run in a conduit - both are designed for direct burial and can overheat if confined in a conduit. You SHOULD use a short piece of conduit where the wires come up out of the ground to protect them from damage, however. When in doubt, read and follow the NEC.
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