Dedicated power,long power cords - waste of time?

If you already have one dedicated line that does not require long (and consequently potentially very expensive) power cords, I would be really cautious about saying you definitely will find an audible improvement adding the two extra lines under these circumstances. If you could plug straight into the wall, you probably would hear a clear improvement. But the really big sonic upgrade seems to be going from no dedicated lines to at least one, which if I understand your post, you already have. Depending on what power cords you are thinking about using, this could be a very expensive undertaking indeed. The lines themselves could be done for less than $500 in most cases, but power cords of this length could easily run many times this amount by themselves. And long runs in cords/cables are never a good thing sonically to begin with.

Rgd
I agree with Chuck, talk to your electrician and get his idea on how to best run dedicated lines close to where your rig is now. There are usually ways of snaking lines from the panel to the new location even without access to the space above or below. The electrician might have to open small holes (for snaking wires) in the walls and/or ceiling but these are easily repaired. Good Luck.

If you decide you really do need to run 20' power cables it's possible to very easily make them up yourself. You can create a shielded power cable for about $75 with some of this:
Cable
One of these:
Male plug
and one of these:
Female plug

There's no soldering involved and it shouldn't take more than 15 minutes to do.

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Contrary to what Zenieth states, there is doubt.

I suggest that you get a long (40 ft?) heavy duty extension cord and plug it into an outlet near your electric service box. Turn off every electrical device on the same fuse/breaker as that outlet. Now you have a "dedicated" line, except that it uses the extension cord wire inastead of Romex. Plug your system into the extension cord, and fire it up. Does it sound different? Now YOU can decide if the cost of a "dedicated" power line is worth it.

By the way, I do have "dedicated" power lines, but that's because my power amps are in the cellar, where running Romex is no harder than an extension cord (well almost) and my front end equipment rear side is in the cellar stairway about 6 feet from the electrical service entrance.
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I agree with Warrenh. I have dedicated lines that come into my room from the outside, then are run along the baseboard of the room for an additonal 15' to where my rig is located. 20' power are expensive and severely limit your choices of cords.

Good luck,

Reg