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Before you call the Electrician.........

Posted by jea48 (A) on October 14, 2006 at 06:31:38

In Reply to: Re: Does he mean isolated ground? posted by halfnote on October 13, 2006 at 21:37:19:

New dedicated audio branch circuits and outlets. Here are some things to think about before you call the electrician.

1) How many dedicated branch circuits do you want? What is a dedicated 120 volt branch circuit?
A branch circuit with a dedicated hot, the ungrounded conductor.
A dedicated neutral, the grounded conductor.
And a dedicated equipment grounding conductor.
3wire multi conductor branch circuits are not dedicated circuits. This type of install has two separate 120V circuits with a shared neutral, plus an equipment grounding conductor. Each of the separate circuits are fed from breakers of each of the two lines in the electrical panel. One from L1 and the other from L2.

So back to the question, how many circuits? Generally , one for each Power Amp. One for other analog equipment. And at least one for Digital.

2) Distance from the electrical panel. How long will the branch circuits be? Don't forget to figure up and down. If they are over 75' to 80' you may want to consider a sub panel. If you do not want a sub panel then the minimum wire size for long runs should be #10 awg copper for all branch circuits. Long branch circuits tend to invite ground loop problems. For long branch circuit runs one thing that seems to help prevent ground loop problems is to connect all the equipment grounds together at the outlet rough-in boxes. This will give you a Star ground close to the audio equipment. Yes you are loosing the dedicate equipment grounding, but if you have to resort to ground cheaters you have no ground fault protection. Food for thought all you are doing is moving the common equipment ground point from the main service electrical panel to a much closer point near the audio equipment.

3) RFI noise. Will you want the branch circuit wires installed within a metallic raceway? EMT conduit or flexible MC cable? If you decide to go this route then you will more than likely want to use isolated ground hospital grade receptacles. The equipment ground wire will be insulated.
If you are not worried about possible RFI noise, then NM-B, (romex, trade name), cable will do, and for less money.

4) Size of wire to use? If less than 50' #12 awg solid copper conductor. For Power Amps I personally would run #10 awg solid copper conductor. Note, Solid copper conductor, no stranded. Stranded conductors are said to cause strand modulation problems.

5) If you want each dedicated circuit totally isolated, then at the rough-in outlet boxes, you will need to decide how you want them installed.

If you use 2 conductor with bare ground NM-B (romex), 12-2 w/grd or 10-2 w/grd, and a standard hospital grade receptacle, and the rough-in box is metal, then each outlet rough-in box will need to be separated from each other. In other words not ganged, connected, together. If plastic outlet rough-in boxes are used then you can use a multi ganged box. Just have the electrician insulate the bare ground wires or make sure they do not touch each other.In this case the outlet cover plate will have to be plastic. With NM-B there is no need for isolated ground receptacles in normal installs. If you want multi ganged outlets and have to use metal boxes and want the total isolated equipment grounds then you will need to use 3 conductor with bare ground romex. The bare ground wires will joint together and with a pigtail bond to the metal rough-in box. One insulated conductor of each NM-B branch circuit will connect to the equipment ground screw on each of the isolated ground receptacles. Note, isolated ground receptacle.

6) Equipment grounds...NO Separate Ground Rods...All equipment ground wires of new branch circuits must terminate in the panel they are fed from. If they are fed from the main electrical service panel then they will terminate on the neutral/equipment ground bar, or the appropriate ground bar within that panel. While the electrician is in your home, have him check all the grounding electrode conductor/s teminations at both ends. Clean and tighten. He will know what to do.

7) Connection of the branch circuits in the electrical panel. This applies for an audio system components that are connected together by ICs.
Install all branch circuit breakers on the same line in the panel. L1 or L2 but not on both...Single pole 20 amp breakers.

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