Home Tweakers' Asylum

Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

RE: Incoming AC legs NOT created equal...

These were run with stranded, individual wires, in a buried PVC conduit...but they may all be in the same clustered group, but the buried PVC only has runs for the audio gear in it.

Hi Rick, thanks for the response.

Though it may sound better than what your friend had before it would more than likely sound even better had he not used the wiring method he used for his 4 new dedicated circuits.

A true dedicated branch circuit does not share the same conduit or cable assembly with any other branch circuits. The reason they should not be installed in the same conduit is the current carrying hot and neutral conductors will induce a voltage onto the other conductors in the same conduit. The same for any AC noise/harmonics that may be present in a circuit caused by a piece of audio equipment.

Even when a dedicated branch circuit is pulled in its' own conduit if the hot and neutral current carrying wires are just loosely pulled in the conduit with an equipment grounding conductor an induced voltage can be induced on the equipment grounding conductor. The induced voltage on the equipment ground can be the cause of a ground loop hum and or noise on the equipment ground conductor.

When a conduit is used it is recommended the hot and neutral wires should be twisted together the entire length of the conduit run. The equipment grounding conductor should just be pulled along side the twisted hot and neutral pair. (Note: Will twisting the hot and neutral together and then pulling them in a conduit meet NEC or local AHJ electrical code? I am not sure. I am sure the twist of the 2 wires should not be too tightly twisted together. That will not meet the manufacture intended use of the wire and therefore not meet electrical code).

I am not a fan of stranded wire either for branch circuits that feed audio equipment. I recommend solid core. #10 solid copper can be a pain to work with though.



Here is a long winded experiment I conducted a couple years ago on harmonics caused by an incandescent light dimmer. The test equipment was just a simple phone tone receiver used to find twisted pair phone cable pairs.

The noise generator I used was a wall incandescent Lutron dimmer. The branch circuit feeding the lighting is a dedicated circuit for the lighting in the room and lighting in a bathroom. (14-2 with ground Romex). With the dimmer set at about 60% the harmonic noise radiating from the dimmer was quite audible. I was able to follow the load side branch circuit wiring up the wall to the 9ft ceiling and to each of 7 can lights mounted in the ceiling of the room.

On the same wall as the dimmer is another dedicated circuit that passes/parallel on the same wall stud with the lighting circuit that is used for general convenience outlets in the room. The dimmer harmonics corrupted the entire convenience outlet branch circuit run in the room.

As for the home run lighting branch circuit wiring feeding the dimmer as I moved from the dimmer to the electrical panel the audible sound of the receiver got weaker the closer I got to the electrical panel. The home run is about 60ft long. Wire is 14-2 with ground NM-B cable. (Romex is a Trade name.)

At the electrical breakers around the breaker feeding the dimmer branch circuit the audible sound was fairly even. As I moved the receiver further away to other breakers the audible sound was somewhat weaker but not by much.

From this same electrical panel I have 2 dedicated circuits that feed my 2 channel audio system. The 2 home runs are about 75ft each. Wire is 10-2 with ground NM-B cable. With the dimmer on, set at 60%, I held the receiver at each duplex outlet of the 2 circuits. All I could hear was the faint normal 60Hz hum of the AC line picked up by the receiver. I could not detect any dimmer harmonics.

What I discovered is the harmonics produced by the dimmer dissipated the further I got away the dimmer to the electrical panel and continued to dissipate the further I got from the panel to the wall duplex receptacles of the 2 dedicate circuits feeding the 2 channel audio equipment.

I should also note the 2 audio dedicated branch circuits were intentionally installed away from any other parallel running branch circuits. Especially any lighting branch circuits Line as well as load. I also kept the 2 dedicated audio circuits separated from one another, parallel run, as soon as possible after getting out of the electrical panel. At least 60ft of the 75ft runs are kept separated from one another. (This eliminates induced voltage transfer as well as AC induced noise from one cable to the other.



Below is a white paper well worth reading.
check out page 16 and then go to pages 31 through 36.

Edits: 06/03/17

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