Isolated Ground Circuit for Home Theater


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Old 03-26-09, 04:12 PM
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Isolated Ground Circuit for Home Theater

My Black and Decker wiring book mentions that an isolated ground circuit is a good idea for powering computers and home theater equipment. It's supposed to provide extra surge protection and interference protection. Since a home theater is part of my basement plans, I'm wondering if they are worth the trouble?
 
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Old 03-26-09, 04:21 PM
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There is no such thing as an isolated ground in a residential environment. The isolated ground and the normal ground would both be terminated at the exact same location.

Just run a dedicated circuit for the home theater and you're set.
 
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Old 03-26-09, 04:34 PM
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Interesting. The book describes using 14/3 cable and connecting the red (and tagging it green) to the ground terminal and then back to the ground bar. The bare ground wire gets connected to the ground screw on the box and the ground bar. They show it using a special orange receptacle indicating the isolated ground.

So, what you're saying is running a dedicated circuit accomplishes the same thing.

But the real question remains, is it worth doing?
 
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Old 03-26-09, 06:07 PM
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Interesting. The book describes using 14/3 cable and connecting the red (and tagging it green)
The NEC does not permit # 14 wire to be re-identified as ground in residential use. Only factory colored green or bare is permitted. The set up you describe is a special commercial setup not used in home wiring.
 
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Old 03-26-09, 06:23 PM
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In theory, What youre describing would be intended to eliminate any interference from Nearby Conduit or metal boxes. The ground would be Isolated from from the rest .

In real life...Once you place a ground conductor on the "BAR", its linked to the rest of the system anyway.

Not worth the trouble, Since as mentioned, A dedicated circuit will accomplish the same thing, Including the cash you saved on the 3 conductor copper.....
 
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Old 03-26-09, 09:41 PM
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Originally Posted by JoeTheZombie View Post
There is no such thing as an isolated ground in a residential environment. The isolated ground and the normal ground would both be terminated at the exact same location.
.
yes there is Joe.

even in a commercial or industrial system, the grounds all are interconnected at the service panel. All an iso ground is is there are no other grounds connected to the iso ground conductor other than at the service panel (including the conduit system if metal conduit is used). In a resi setting using plastic boxes and NM, as long as the ground is not interconnected anyplace other than at the service panel, it is an iso ground.
 
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Old 03-26-09, 09:45 PM
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Originally Posted by Unclediezel View Post
In theory, What youre describing would be intended to eliminate any interference from Nearby Conduit or metal boxes. The ground would be Isolated from from the rest .

In real life...Once you place a ground conductor on the "BAR", its linked to the rest of the system anyway.

Not worth the trouble, Since as mentioned, A dedicated circuit will accomplish the same thing, Including the cash you saved on the 3 conductor copper.....
actually, it is intended to prevent interference caused by induced currents on the EGC of other systems affecting the iso ground equipment.

and yes, the grounds all, even with an iso ground, are connected at the main service.

if you have a dedicated circuit, as long as the EGC does not connect to any other ground or grounded metal before reaching the main service, you do have an iso ground.
 
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Old 03-26-09, 09:53 PM
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Is your B&D book old? Or is it recent? What's the copyright date?

The code-violating suggestion in that B&D book has been talked about now for many years. I would hope that B&D would have corrected their serious error by now.

Not only is it a useless idea (for residential), it vioates code.
 
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Old 03-27-09, 12:26 AM
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I am pretty much the same page as Nap is talking about the isolated grounding system.

Most NM's if done right it is self isolated grounding by design as long you used plastic junction box and the bare or green ground conductor is not tied to other ground conductors at all.

However for the OP's info about the Black and Decker book that I am instering how old that book is that.

I know I did have very old Black and Decker book when they came out a decade or so back it did mention that can remarked the red conductor as green however the only time they did that in old code days if you have BX/AC cable I doub't the NM were not allowed to do that format.

By modern codes it is no longer legal at all it was rewritten quite few code cycle back I think in late 80's not sure when they were in effect that time.

Merci,Marc
 
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Old 03-27-09, 11:16 PM
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A good ground is essential to the proper operation of an A/V system. An isolated ground (one that has no other connections between the system's receptacles and the service panel) is better than a non-isolated ground. To achieve this, a circuit is usually home-run to the panel and dedicated to the system on its own breaker. The rule of thumb is to provide "one and only one" ground for the entire system. Electrical ground, that is ...

If you're an audiophile purchasing high-end equipment, or if you plan to use professional-grade equipment, that equipment will also have an audio ground. This is different from electrical ground. The audio ground is not part of the electrical system and has no connection to the device chassis and/or ground pin of the AC plug. It therefore must be connected to a separate ground rod with no continuity between audio ground and electrical ground. Further, there must be no voltage potential between the audio ground and the electrical ground.

If even one device in the A/V system does not conform to this scheme (by having its signal ground internally connected to chassis ground), the signal ground must be either disconnected at the offending device's inputs and outputs, or the entire system must be tied to the electrical ground. In the latter case, the separate ground rod is not used.

Another caveat: Many LCD and plasma TVs now connect the incoming cable ground directly to the chassis, which is in turn connected to the ground pin of the AC plug. Unless an isolating transformer (a.k.a. "balun") is used on the incoming cable line, the TV causes ground loops -- which manifest as noise in the audio and "hum bars" in the video picture -- and even dangerous voltage potential between metal system components and ground.
 
 

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