What type of wire for dedicated 20A AC lines?

I just completed my 50 foot dedicated AC.

Your question was what wire to use.

I believe I addressed this issue with about the best wire available.

Oyaide high quality copper three wire 10 gauge.

This very special cable is available through the US distributor, www,lotusgroupusa dot com. Joe Cohen in NorCal. 
This cable is very close to a good quality power cord. Its construction includes 2 copper grounds in addition to the main three wires. 1 a ribbon that wraps around the main 3 and a second one in a thin copper braided wire.

To get the best, one has to pay. My 50 feet cost $4K. In addition I terminated the run with two Oyaide duplexes and carbon fiber face plates. This was $1200 more.

And my electrician was another $2200. My run was complex through the attic.

Was $7400 worth it? You bet! The improvement was global. I got about a 25% better system. Clean, punchy, stunningly real!

The only catch is that none of this Oyaide stuff is UL approved. But the Japanese standard are way beyond those in the States. And I did not touch the house AC system. Still, you have to find a licensed electrician who is willing to deal with non UL. I went through a couple and luckily found a guy willing to do the install.

And I had to pay him a consultant fee to talk with Joe Cohen on how to deal with the unique Oyaide cable.

The main issue is wire. For me, there is only one.

It would have been really sweet to run a parallel 10ga Romex and charge for  tickets to demos of the improvement...

@jea48  Look, I don't know how old any of poster's houses are or if they are wired with cloth-covered wire or built in 1930 or whatever, and I am sure there are reasons that exist for some upgrades, etc. in some situations. 

Also, if you think running a "dedicated" wire of some specific material to your home stereo will help it sound more like a live concert hall experience, who am I to tell you it doesn't?  Or adding a voltage regulator or whatever else your electrician tells you to do. 

I guess if I had a pair of Audio Research Reference 750 SEL amps, I might be tempted to look into the power requirements from my panel to the amps.  What happens BEFORE the panel, well, I guess calling FPL down here would get me lots of help (laughing--they don't actually talk to customers).

However, as a former dealer, I can tell you that every electron I ever interviewed was non-committal about their traveling preferences along signal or power wires, so I can only base my POV on that.  Same for "directional" patch cords made out of elemental silver or titanium with solid gold ends...OK, gold ends do make a  difference in corrosion...that cost $100,000/meter are wonderful for bringing out that 3rd chair violin, I am sure.

Whatever brings that orchestra into your listing room is fine with me,I guess.  I wonder what the rock bands require power-wise in the auditorium where their concerts are recorded live?  Not that the recordings are "managed" before they are released, of course...

Cheers!

If the UL listed "whatever your plugging in" draws less than 20 amps 12/2 is great. There will be no voltage leakage from a 50 foot run, 500 feet maybe. It depends on what else is on the circuit Since these are dedicated circuits there is no need to worry about enough amperage or voltage. Cleeds you are wayyyy off base. Whether it is 12 awg THHN in a conduit or 12/2 Romex doesn't matter. If it is a 20amp circuit, 12/2 always meets NEC Code.

To chime in on an update.  I’ve since engaged @kingrex ’s services to spec out my AC lines and other fixes for my electrician to follow.  Rex has been doing this for years and as he said above, I’ve since learned that it goes way, way beyond just the gauge of the wire…

Here is what Michael Fremer of Stereophile said about Rex working with Garth Powell of Audioquest, when they and others joined forces to resolve Michael Fremer’s AC issues: