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In Reply to: RE: interesting posted by Ugly on June 29, 2007 at 22:28:07
Separate dedicated circuits are the way to go. If you can avoid conduit, I think that would be best. Conduit is available in steel, aluminum, and PVC. Steel would have nonlinear magnetic interaction with the power current. Aluminum would avoid the magnetic interaction, but would increase capacitance of line- and neutral-to-ground. It would also have acoustic ringing problems. PVC should be the most neutral of the choices, but would still introduce some sonic vibation behavior. If you have to have conduit, try to wrap the stuff with rubber tape after the inspector has blessed it.
Cheap house wire cable is insulated with PVC. Oyaide makes polyolefin-insulated, carbon-damped cable, but it is very expensive. If nothing is too good for precious, I would look into this stuff.
Follow Ups:
With me being involved as an ameteur AM radio station operator/ local wireless and wired network administrator (of my home)/ member of a high techish suburban community/ near bustling commercial and military communications and navigations signal hubs my audio equipment in is in the middle of what might very well be considered RF hell. I see the single ground wire, dedicated lines bundle, in conduit, in-wall, service run as a great weapon against RF and significant reducer of the length of the "necessary" ground loops a seperate dedicated lines suffers from and can't seem to let go of this thing. The problem is as I understand it, the only way to pull off this holy grail desired feature of a single ground there has to be a conduit in order to satisfy code. It is safe to assume that if I didn't use the lowest electrical impact PVC conduit material that the conduit approach is no longer an option and my dreams of this single ground wire system go poof in a wisp of smoke.
Obviously PVC isn't a perfect dielectric material so I understand your comment about how it may still be an imperfect solution signal integrity wise. My gut feel is that is less of an issue in my environement than RF immunity is. I don't see a way around that barring finding some more electrically inert conduit material. The other problem with this approach that you mentioned, vibration problems, can be dealt with almost entirely. I can as you point out mechanically damp the conduit if necessary. Maybe some of that expando foam insulation stuff in the wall surrounding a rubber tape wrapped bundle might keep it all holding still.
There are also imperfections in the seperate dedicated line approach. It introduces longer parallel lengths of ground conductor. This means more potential for noise energy to be injected into the signal vs the single wire approach via crosstalk and radio signal reception. To battle the RFI problem the bundle can be more tightly packed. However the tighter packed bundle would have the tradeoff of being more likely to have crosstalk issues. To battle crosstalk issues the bundle may be more loosly packed but that means a tradeoff in RF immunity performance.
What confuses me about your post is it's tough to tell exactly why you prefer a seperate set of dedicated lines over a bundle in PVC that has one low impedance ground wire. The question is: are the noise/signal distortions tradeoffs for the conduit approach worse than the noise/signal distortions tradeoffs for the seperate dedicated lines outside conduit approach you are recommending, and under what conditions is it true? I guess my big problem here Al is my little voice inside is contradicting what you are saying slightly. This worries me a little because your obviously an intelligent and thoughtful fellow. This is a general topic which is difficult to talk about in specifics since everyones situation is different.
I like separate circuit cables because of the hot and neutral isolation they provide. In an environment like yours, a single ground wire would be preferred. It is acceptable per code, as I understand it (disclaimer: I am not a licensed electrician), to tie the separate ground wires together at the audio system. This would almost be as good as a single wire. Almost, because the individual loops between the audio system and the breaker panel can still support resonance modes. The difficulty is finding an electrician who will install exactly what you want, and not try to talk you into a subpanel. A subpanel, even if fed with heavy wire, defeats the isolation afforded by separate dedicated circuits with cables back to the main panel.
A metal conduit must be grounded, and makes a second ground circuit from the breaker panel to the outlet box. A metal outlet box will tie this circuit to the ground wire if you use any audiophile outlet I'm familiar with. Nylon screws and washers to mount the outlets would break the outlet-box connection. I'd prefer a plastic box, but I don't know if such are allowed with metal conduit.
Thanks for replying. That clears things up nicely.
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