How to connect garage electric panel

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My main house panel has a 30 AMP breaker that controlling a single line that runs to the garage and has only a receptacle attached to it. I have a complete main panel box/100 amp breaker and other breakers that were taken out when the main panel was recently upgraded to 200 AMP. I want to have several separate lines in the garage for door opener, work bench, lights, etc. My question is how do I hook up the line to the extra panel? Do I just connect to the 100 amp main just so that both sides of the panel box are energized and then connect the couple of lines I need in the garage to the individual 15 AMP breakers in the usual manner? Your input is appreciated. John
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JohnF wrote:

I assume you'd like to use the existing wires.
Do you need 240V, or is 120V adequate? What size wire is the existing circuit? The existing 30A breaker to a single outlet is probably done incorrectly unless it is a clothes dryer outlet, so I don't want to make any assumptions about what you are starting with.
Is this an attached garage or detached?
Bob
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Sorry I left out key info. The garage is detached and is approx 50' from the main house panel . It is a 240V line; the wire is #12/3 plus ground. At the moment only a 120v leg is attached to a 15A receptacle. I want to use the existing wire that is running from the house to the garage. Thanks. John

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JohnF wrote:

John If the wire is twelve gage then there is no need for any panel in the garage. Just change the breaker from a thirty ampere to a double pole twenty ampere breaker. At the garage you install a switch box that will hold a two pole single throw switch. The black wire goes to one pole of the switch the red wire to the other pole of the switch with the white spliced through and the green/bare bonded to the switch strap or yoke. The switch should be rated for the full twenty amperes but you could use two separate single pole switches if you preferred. A single two pole switch is better practice. The switch will serve as the building disconnecting means and it must be located very close to were the wires enter the building. The circuit that you will then have is called a multiwire branch circuit. You are allowed to use two single pole breakers on that circuit but one two pole breaker is better practice for residential property. If the circuit will supply a 240 volt load, such as a large unit air conditioner, in addition to the 120 volt loads then you must use a two pole breaker to protect it and a two pole switch as the building disconnecting means. That circuit will give you the equivalent of two twenty ampere 120 volt circuits without running another wire. The circuit for your work bench receptacle outlets will be connected between the white and black and the circuit for the lights and door opener will be connected between the white and the red. Each circuit will then have 120 volts with 240 volts between the black and red. That is what allows the two circuits to share the white neutral. -- Tom
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Thanks for the input. So do I understand this then that I simply install a 20 amp wall switch at the garage entry point and a panel with 2 pole breaker? Again thanks.

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JohnF wrote:

John The new two pole, twenty ampere, breaker is installed in the panel at the house were the circuit to the detached garage originates. You don't need any new panel in the garage. Just install a switch or switches at the garage to function as the required building disconnecting means. -- Tom Horne
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HorneTD wrote:

But if you have a salvaged panel (which if I remember right, you do), you *can* use it instead of the switches. That might be handy if, say, someday you convert your air compressor or table saw to 240V.
For just a 20A feeder, I think I'd use a 30A air conditioner disconnect as my building disconnect (they are really cheap), and from there split into a couple of 20A 120V circuits.
The most important thing is to replace that 30A breaker in the house with a 20A to match you #12 wire size.
Bob
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Thanks Tom. I am taking 2-pole switch to mean just like a light switch. Am I then just running the lines from the new 2-pole switch box to the future garage door opener and work bench? This is certainly an easy and fast way but without breakers in the garage if a line overloads for some reason I can't reset from the garage which is what I would like to be able to do. John

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JohnF wrote:

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You can have breakers in the garage if you use a small panel at the end of your twenty ampere feeder but if the overload is caused by the loads on more than one of the branch circuit breakers in the garage it will still trip the feeder breaker back in the house panel. With the feeder having a capacity of twenty amperes installing a sub panel in the garage is not worth the work involved. If you do install a sub panel you have to build a Grounding Electrode System for the garage. With only a single multi-wire branch circuit a grounding electrode system is not required.
Someone else has suggested that you use an air conditioning disconnect as the garage building disconnecting means. The problem is that the building disconnecting means must be "suitable for use as service equipment" and most air conditioning disconnects are not. The exception to that rule allows the use of "snap switches", which is the code language for an ordinary toggle switch, but that exception does not permit the use of other types of switches or pullouts that are not "suitable for use as service equipment." The exception is only meant to permit the use of snap switches for residential outbuildings. If any more elaborate disconnect is needed then the device used must be listed by an electrical testing laboratory and marked "suitable for use as service equipment." -- Tom H
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All understood and much appreciated Tom. I will run it as suggested and not be concerned about resetting in the garage and also be sure to install the correct "2-pole" switch as cautioned by Chris in a sub posting. The info here is always on the money. Again thanks and happy BBQ'ing. John
"HorneTD"

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Not quite. A two pole switch switches two circuits at once. That's rare in light switches. Light switches usually come as "one way", "two way" or "three way" - which isn't the same thing at all, and won't properly switch 240V.
You might wish to consider something a bit beefier than a light switch acting as a disconnect.
While a light switch works fine IF there's nothing running on the circuit when you operate them, the usual ones won't like switching current flow to motorized equipment for very long.
Electrical codes do not permit the use of standard duty light switches (or breakers for that matter) acting as the power switches for motors.
Horsepower rated switches (or "real" power disconnect switches) are better.
If you don't expect to be operating the switch that much, and you make a habit of ensuring that everything is off when you do operate the switch, it's probably fine.
Don't know how picky an inspector might be.
A decent two pole switch is likely to have a horse power rating on it - look for that when buying the switch.
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JohnF wrote:

A two pole switch is similar in appearance to a "light switch" but it has four screw terminals rather than two. A common single pole switch can open and close one conductor, a two pole can control two conductors, a three pole three conductors and so on. The code does allow you to use two single pole toggle switches for that purpose but a two pole switch would be best practice because it permits you to deenergize the entire garage with one switch rather than two. -- Tom H
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CAREFUL! If the OP walks into a electrical store and buys the first four screw terminal switch he sees, he'll end up with a 4-way lighting switch. That would likely dead short the circuit - kaboom!
He needs to make absolutely certain that the switch is described as two pole. A two pole switch may have more than four terminals (ie: a DPDT has six, a DP3T has 8 etc), but he only needs four.
Electrical wiring duty units will usually only have four.
[The switch terminology clash between the electrical and electronic industry is _extremely_ annoying. An ordinary 2-way switch is SPST (or 1P1T). 3-way is SPDT (aka 1P2T). A regular 4-way isn't describable that simply. In the electronic trade it'd be described as, I think, a "2 pole reversing switch".]
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that
Your questions are to vague to even start trying to help.
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You say it is a 30a outlet. 30a 240v or 120v? 3wire or 4wire?
I am going to "guess" it is a 30a 240v with 3wire. If so, then what you want to do is impossible. A subpanel requires 4wire.
All you could do (and I doubt it would be legal with the old breaker box) would be to change the circuit to 120v, run it to the box and take 2 or 3 120v circuits out of it.
If it is infact 4wire, then sure it can be done; but you probably don't want to do it yourself.
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toller wrote:

Is the garage attached or detached? How many wires are run to the receptacle? -- Tom H
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A subpanel requires 4wire.
TOTALLY FALSE!!!. In a DETACHED STRUCTURE, provided there are no other metallic paths to the home, a 3 wire run is fine. You must bond at the garage, and have a ground rod, but that is easy. If the garage is attached, this would not be kosher but the garage is detached. Remember the rule "leeves as a feeder, arrives as a service"

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Al wrote:

We don't know that yet. John hasn't answered that question yet.

Best regards, Bob
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I stand corrected. Why is a ground rod allowed on detached buildings, but not on attached buildings?
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either go to the library and educate yourself or call an electrician. possibly both.
randy

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