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j.heiser 05-10-2010 11:25 PM

Help fixing garage electric for Home Theater

I know the simple basics of electric and know a few electricians that are always too busy to come over and take a look at this hook up for me so it looks like I'm going to take a wack at fixing this.

Heres the basics:

My garage is wired as a sub-panel off my house. The breaker feeding the line going to the garage is a two post 30 amp breaker. The box inside the garage is a small 4 circuit breaker box. I have one 15 amp breaker running six 60 watt recessed lights along with outside lighting. I have two 20 amp breakers running the outlets which I just replaced (15 amp outlets). Half the outlets in the room are on one breaker (4) and half on the other (4). I have space for one more breaker in the box.

My issue is when I used to run my fridge and projector the picture on the projector would be affected when the fridge compressor turned on. Now, I plan on running surround sound, fridge, projector, tv when projector isn't in use, and an air conditioner, along with other small things. So how can I set this thing up and any ideas of what is going on? When I put a tester on the wires feeding the sub panel the 220v light comes on along with the 115.

AllanJ 05-11-2010 07:04 AM

You can add another breaker if needed but there is no choice other than plugging the projector into a receptacle on the side of the 220 volt line opposite from the refrigerator.

Get a power conditioner and surge suppressor to "clean up" the power fed to the projector. Get one that plugs into the wall receptacle and then you plug the projector into it.

For a detached garage, if you don't have enough power altogether, you will have to replace the subpanel feed (if it is 10 gauge) with a fatter cable, then you can put in a breaker for it back at the main panel bigger than 30 amps. You will also need a new, bigger, subpanel, especially if you want to install an air conditioner.

For an attached garage you can string additional cables as home runs (nonstop) from additional breakers in the main panel.

Is all the wiring including to switches and light fixtures served by the 20 amp breakers 12 gauge or heavier?

J. V. 05-11-2010 10:41 AM

I would keep what you have and run a new 20 amp circuit to the Home Theater system receptacles. Install several receptacles at the system and do as Allan said. Get something from the electronics store to condition this power. Buy the best possible strip or strips you can afford. Good luck.

j.heiser 05-11-2010 11:05 AM

All of the cable to the outlets are 12 guage. I just wired all of the new recessed lights using 12-2 romex cable. I was thinking I will put the air conditioner and fridge on one 20 amp breaker, all the lights on the 15 amp breaker, the other half of the outlets on the 20 amp breaker. I'm thinking I will run a 12-2 romex cable directly down from the box and install a heavy duty 20 amp outlet for all electronics. My electronic stand is going to go directly under the box so from what I hear have the things that pull the most power closest to the box is good.

The garage is detached. Do you guys think there is even enough power getting out there? Is it possible to bumb the breaker on the main panel in the house up?

sparks1up 05-11-2010 11:22 AM


Is it possible to bumb the breaker on the main panel in the house up?

Do you mean "bump" the breaker up to a bigger size? If that is what you mean we need to know what size wire is feeding from the breaker to the sub panel! If it is #10 the answer is NO! If it is bigger than #10 then you might be able to.

What size is it?

j.heiser 05-11-2010 11:48 AM

I just checked the cable and it was hard to find but it says 10/2 cable.

Will I be okay wiring one additional outlet for all electronics on one 20 amp breaker? Or is the air conditioner, fridge, projector, and surround sound going to keep popping breakers?

Yoyizit 05-11-2010 12:47 PM


Originally Posted by j.heiser (Post 440233)
My issue is when I used to run my fridge and projector the picture on the projector would be affected when the fridge compressor turned on.

The resistance of the cable feeding both may be 0.2 ohms. This relatively high impedance is why the compressor starting is able to influence the projector picture.

You could run a separate line powering the compressor load back to the breakers.
The panel is a low impedance point, maybe 0.02 ohms, so they'll be much less effect on appliance voltage when the fridge compressor kicks on.

Ideally, if the panel provided a zero impedance point the compressor starting would not affect any appliance voltage.

AllanJ 05-11-2010 01:24 PM

A lot of video projectors nowadays consume less than 200 watts.

I would expect the sound system to consume less than 200 watts continuous with any peaks above 200 watts short enough not to trip the panel breakers and short enough that the average power draw is less than 200 watts.

Wait a minute!

You said the tester lights up the 220 indicator as well as the 115 indicator.
You said the cable from house to garage is 10-2.

Something is not right. You cannot have both 115 and 220 volt circuits in the garage fed by a two conductor cable. You may not use the bare ground wire in the cable as a neutral.

The refrigerator and a 115 volt air conditioner and the theater may well exceed the 30 amps by 115 volts that is the most you can get via the 10-2 cable. A 10-3 cable would have given you two allotments of 30 amps by 115 volts some of which can be drawn as 220 volts. If you have to run a new cable you might as well go for a 6-3 copper cable that will give you a lot of room for expansion in the future (60 amps by 220 volts).

j.heiser 05-11-2010 09:30 PM

What do you mean by two allotments of 30 amps?

AllanJ 05-12-2010 07:18 AM

Two allotments:

With a 10-3 cable connected to a two post 30 amp breaker back at the main panel, you have 30 amps at 240 volts using both hot wires, or you have 30 amps at 120 volts using one hot wire and neutral and 30 amps at 120 volts using the other hot wire and neutral. But you cannot get, say 45 amps at 120 volts on one side if you limit yourself to 15 amps on the other side.

(When you use 240 volts, the number of amperes is taken from both allotments for example 10 amps at 240 volts leaves 20 amps at 120 volts available on one side and 20 amps at 120 volts on the other side.)

gregzoll 05-12-2010 07:48 AM

Personally, I would have a sub for just the electronics coming from the house, with a surge/spike protector protecting the equipment off of that panel. Home theater equipment is not meant to be used in a space that is also used for a workshop. If you are able to pull a new feed for just your electronics from the main, I would do that, instead of using the existing panel for the garage/workshop.

j.heiser 05-12-2010 09:11 AM

Allan- That makes a lot more sense now. Thanks for the description.

If I was to run a whole new line, say the 6-3 cable, it would be a real pain. I could easily run from the box in my house all the way through my basement. The problem is when I punch through the back wall I have about 15' to get to the garage and this is nothing but concrete. I can't see anyway of running the wire without tearing up some of the concrete or else I would def change the panel to a larger panel.

The only solution I really can see is running the a/c and fridge off one 20 amp breaker, the lights off the 15 amp, the other outlets off the 20 amp, and install an additional 20 amp breaker with dual 20 amp heavy duty outlets protected by a surge protector and power conditioner.

I should say that when the projector would get lines going through it from the fridge kicking on, they were plugged into the same outlets. Also, whatever genius wired the panel installed 2 30 amp breakers to run those outlets. I do get slight brown outs with the lights when I run saws or anything like that. The garage won't be used as a workshop though, strictly a HT.

Yoyizit 05-12-2010 09:59 AM


Originally Posted by j.heiser (Post 440804)
I do get slight brown outs with the lights when I run saws or anything like that.

Bad connection at the panel neutral or one of the hots.

You can test for that with a DVM. A 10A, 120v load should drop an outlet voltage about 3v and a 20A, 240v load should drop the 240v at the panel by about a half volt.

J. V. 05-12-2010 10:08 AM

Your quote: " My garage is wired as a sub-panel off my house. The breaker feeding the line going to the garage is a two post 30 amp breaker. The box inside the garage is a small 4 circuit breaker box".

I am glad Allan questioned this as there is something wrong. You do not have a compliant feeder going to the garage. A neutral conductor cannot be a bare wire, it must be insulated. So you have only 230 Volts feeding that panel. "Panel" is the keyword as a 230 volt branch circuit could be installed in this manner. A panel cannot be installed this way unless your have two hots and a neutral that are insulated. What you have is a 230 volt circuit and no more. You cannot connect anything to the panel except 230 volt loads. So no lights, no fridge and most likely no AC. The original installer is using the ground as the neutral. This is not acceptable. You say the feeder is a 10/2. That's two insulated wires and one bare wire, so lets make sure that is what you meant to say. If you have a true 10/2 NM (Romex) cable you must pull a new feeder with four wires. Or turn this panel into a 120 volt panel. You cannot pull a single wire to accommodate/ make a new neutral.

While your system works, it is not compliant as the neutral must be insulated. The neutral is a current carrying conductor.
A service is different as the un-insulated neutral/ground connection only exists at the service panel or disconnect. A service cannot pass through a structure to supply another service. So you have a feeder and you must address it as one.

Either turn this existing panel into a 120 volt sub panel or pull a new 4 wire feeder. H-H-N-G. If you turn it into a 120 volt sub, you will need to remove the 30 amp two pole breaker, install a 30 amp single pole breaker, use one of the insulated conductors as the neutral and the other the hot. Leave the bare connected to the neutral/ground buss bar.
By the way? What colors are in the existing feeder cable? White/Black/Bare or Red/Black/Bare. If its the latter it cannot be re-identified as a neutral.

PS.......You have never told us if this sub panel is in an attached structure or if the garage is connected to the house. It makes no difference, but is good information for those trying to assist you.

j.heiser 05-12-2010 10:17 AM

The cable is white/black/bare and the garage is detached. It sits about 12' behind my house and about 3' to the left. Pulling a new line would be easy except I have concrete from my garage to my house and would probably have to tear that up for the line. I will try and take some pictures or draw a diagram as best I can to give you an idea of what we're looking at.

I'm pretty sure the cable read 10/2. It's extremely faded and hard to make out but I'd say I'm 90% on that.

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