Household ground loop fix?

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Old 04-25-08, 01:16 PM
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Household ground loop fix?

Hi all,
I was wondering if any of you knew the code for 110V household electrical code for grounding. I had a ground loop from my TV to my home theater (TV on a different circuit than the home theater in a closet) and yesterday I just wired both the grounds together. Is this a violation of code or a safety problem? I can't think of anything that would be particularly unsafe. For all intents and purposes, the wires are grounded together at the ground strip in the service panel so what's the difference wiring them together in the wall? Just curious if I might have missed something. Please let me know.

-Bruce
Texas
 
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Old 04-25-08, 01:39 PM
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interesting question

I assume that connecting the two grounds fixed a TV reception or audio hum issue?
If connecting the two grounds together made a difference, then that says there was some voltage difference between the two grounds; further saying that at least one of the grounds was carrying current. This is a bit suspicious with a general purpose circuit (no oven/dryer).
Connecting grounds together in juction boxes is generally code approved, even if from different circuits. Actually, you NEED to connect different grounds together when they come into a metallic structure. So, just how did you connect the grounds, as part of the house wiring system or on the user side of the receptacles? Also, verify both circuits orginate from the same load panel or subpanel.
 
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Old 04-25-08, 02:20 PM
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Yes, 60hz hum is gone

Yeah, so I originally had everything on the same circuit, but I was tripping the breaker when I had a small space heater on so I ran a dedicated run from the service panel to the closet. The TV, since it was in the living room, stayed on the original circuit, and the home theater moved from outside to inside the closet. Plugging the system back to the original circuit solved the hum, but still tripped the breaker. Unplugging the TV removed the hum. Both runs to the service panel are over 50 ft. One run is 14ga and the new run is 12ga.

I took a 24" 12ga wire piece I had lying around and ran it from one box to the other box (they're not far apart at all) and wired it to the bare grounds on the screw terminal side, not the plug side. The runs all go from the main breaker (service panel) box in the garage.

You're right though, it does indicate that there was voltage present on the ground. I probably should have measured it before I grounded it just to see how much. Would it be worth checking? I suppose so. it's not that difficult to get back in there.
 
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Old 04-25-08, 02:35 PM
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I hope you relized two diffirent wire size required diffrent breaker size the 14 gauge wire size reqired 15 amp breaker while 12 gauge wire size reqired 20 amp breaker but however there is one thing you have to watch out when you add a new peice of wire you have to check the exsting wire size to keep the breaker the same size.

now let get to next step what type of oringinal wire you got at your house like BX cable or NM without ground ??

and some time you will run into bootleg ground which it is not a very safe way to ground it.

the bootleg ground mean someone ran a short jumper from netural to ground that useally found on the circuits which it dont have ground wire there.

some case if you have BX cable sometime it can get loosen over the time or corroded then you have issue

to check between netural and ground with proper system N-G it should read 0 volts.

hope that should help ya some details you are looking for

Merci,Marc
 
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Old 04-25-08, 02:51 PM
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I'm not sure which question you were actually answering

Everything I've wired has a bare wire ground. Everything, as far as I understand conforms to the basic understanding I have of code. As I mentioned, the ground wire I added was from the grounds of the wires going to the receptacle.

On a different note, I don't understand why I would have to have matching sized breakers for two different circuits of different gauge wire. When I said I ran a new run, I didn't remove the old wire, I added a whole new circuit.

Also, just a matter of wording: 12 ga wire doesn't actually require a 20A breaker, though it can support it.
 
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Old 04-25-08, 03:16 PM
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Originally Posted by brucechang View Post
I'm not sure which question you were actually answering

Everything I've wired has a bare wire ground. Everything, as far as I understand conforms to the basic understanding I have of code. As I mentioned, the ground wire I added was from the grounds of the wires going to the receptacle.
ahh ok then you are allright there

On a different note, I don't understand why I would have to have matching sized breakers for two different circuits of different gauge wire. When I said I ran a new run, I didn't remove the old wire, I added a whole new circuit.
sorry my bad i miss read it sorry for my error.

Also, just a matter of wording: 12 ga wire doesn't actually require a 20A breaker, though it can support it.
really ?? for normal genral circuits the 20 amp is the max size is allowed per NEC / CEC code there are few specal extemts but i will leave it out for now.


anyway let get to the main topic for now you did the correct way tie the ground [ bare or green wires ] together that is fine.

what i am refering to the oringal house wire if they are orininally wired or it been upgraded before ?? because sometime along the circuit someone did the repair or something before you have this place and some case did not used the ground wire at all or it was never exstied in that era.

you may want to check the exsting ground wire from breaker /fuse box to the ground rod or water pipe and make sure they are in good shape as well.


{ quick tibbit here the bare ground wire start show up in late 50's~ early 60's but got widespread at latter 60's and allthe way to modern time }


Merci,Marc
 
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Old 04-25-08, 04:22 PM
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It would be much better if you could run the entire A/V system on one breaker. One dedicated circuit home-run to the panel with it's own home-run ground is best.

Your A/V system still has a voltage potential (difference) between the TV and sound system ground, only now it's relying on the new wire you ran. As long as the new wire has less resistance than the A/V loop, your hum will be minimal. (Listen close, though. It's still there. It's just a lot quieter.)

There is also a good probability that the new "12 gauge" circuit is on the opposite 120 volt leg from the "14-gauge" circuit. Not a good idea for an A/V system. Any unbalanced condition in the neutral can cause voltage potential to show up on the signal grounds. (And in most homes, the two 120-volt legs are almost never perfectly load-balanced.)

A ground loop occurs when the signal wiring in audio and video systems bridges two electrical grounds that take different paths -- and different distances -- to the panel ground. In your case, the distance from the audio system's receptacle to the panel is longer or shorter than the TV's circuit ground. The "loop" is created through the signal wiring's shields, which are connected to the equipment chassis, which in turn are connected to ground in the receptacles. It doesn't take much: A few feet of difference can mean a few millivolts.

You can eliminate this problem altogether by isolating the signals from each other. In the audio, a 1:1 audio isolation transformer is installed on each signal cable. In the video, back-to-back "baluns" are used to prevent a direct connection between the TV's cable input and electrical (chassis) ground.
 
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Old 04-27-08, 04:57 PM
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I agree with you that it'd be better, however, I don't have that luxury because I can't get to the box that the TV runs on. I would definitely want everything run off the same circuit if possible but that's not at my disposal at this time. At this point it's more of a question of, "is what I did okay" not so much, "what would you do if it were you."

Also, I'd be willing to put an isolation transformer in there, but again, it's an HDMI cable and I didn't want to bother with trying to hack the cable and deal with it. Running a ground between the circuits was easier and if it gets the job done, why mess with it further? I did run the two breakers from the same side of the service panel so I'm pretty sure that we're on the same 120V leg. Not a problem there.

In regards to French's reply, I was saying exactly what you said, that 20A is the max you can put on a 12ga wire. Your statement said 20A is required, which some could take as you have you use a 20A and can't use a 15A breaker. It was kind of a nitpick on my part and I apologize.
 
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Old 04-27-08, 05:08 PM
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That allright Bruce we try to help you with it.

For the rest of details i will let Rick Johnston deal with this one due he have pretty good knowage on the set up you are descirbing.

but i am little condersering senice you mention two breakers on the same leg the hot conductor is not a issue but the netural conductor it may have issue and possiblty you got one of the circuits tied together somewhere sorta like " bridged " over which what i am describing if one breaker tripped and second breaker still feeding power to that set of circuit and it can get pretty messy with it and i am sure you allready mapped out the circuits on the breaker box.

Merci,Marc
 
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