Dedicated Line, Surge and Safety

As Ez2hear said, 12ga is the minimum gauge for a 20A circuit. It's preferred by electricians over 10ga precisely because it's thinner. Thinner is easier to install. If you've ever worked with 10ga NMS, you know it is a major PITA - it makes any job take about twice as long.

12ga works fine for most 20A circuit applications. The only REAL reason to use it (i.e. besides tweaky weird audiophile reasons) is if you have to go a long distance. There's a maximum length spec for 12ga on a 20A circuit, and if you exceed that you need to use 10ga. BTW there's not too many residential situations that would cause you to exceed the max length. An almost sane reason to use 10ga is if you're going from one side of your house all the way to the other and it's a long way, 10ga will cause a little bit less voltage drop than the 12ga. That's one to use on more imaginative electricians.

If you've got one who just stares at you like you've lost your mind when you say you want a 12ft run of 10ga for your 20A circuit, tell him you may need to upgrade it to 30A at some point because your next hobby will be arc-welding! :)

10 gage is not overkill. You're house will not catch fire either by surges or because #10 wire happens to be capable of carrying extra current - the circuit breakers and the grounding system protects against that.

With respect to surges: surges are a temporary overvoltage or overcurrent condition which can cause thousands of amperes to flow. Your circuit breakers are rated for 10,000 amps of short circuit capability - which gives adequate protection for lightning strike surges and arc faults. However, a lot of capacitive energy can sneak through - therefore the purpose of the surge protector. Also, heavier gage wire has a higher fault current capability. For example, #10 wire can clear an 8,500 amp short in only 1/2 of a 60Hz cycle and withstand temparture spikes up to 250 celsius.. a #12 wire can withstand 5,000 amps. That's why a circuit breaker is rated to clear 10,000 amp shorts - a safety factor of two. So, technically, #10 wire offers better protection if by chance your circuit breaker doesn't clear the fault or a lightning surge current misses the ground rod. Now you know more than your electrician.

As for lengths of runs: a longer run will cause a higher voltage drop. Generally, you want to keep the voltage drop to 2.5% or less at your outlet. For a #12 wire, keep the length under 30 feet and voltage drop will never be a problem at max current draw of 20 amps. For #10 wire, you can run up to 60 feet before you have to consider voltage drop. Also, power supplies can operate at spec down to 114 volts (5% voltage drop) so you can double the above lengths and still be okay.

There is another "real" reason to use fatter wire: sound. My monoblock amps sound WAY better when I rewired with 10 wire. #10 wire has less inductance/capacitance to the instantaneous current demand called by the amplifiers.

Rex, the longer the loop distance between the dirtier digital onto its ac line to the analog preamp's input the lower the expected noise floor....
Gs5556, nice post. So why does the 10AWG sound better? It's TOTAL inductance is actually higher than the 12AWG, but maybe not as a ratio to its resistance, or current-handling capacity. If it sounds better I postulate that it's because it stays isothermal through those instantaneous current demands. Yes, 10AWG is overkill in these circuits, as even tiny temperature fluctuations won'y occur except perhaps with the very largest amps. There's some work to do here, as the normal electrical specs allow ratings that reflect a fairly large temperature rise...maybe WELL past what's audible! Is it the voltage drop that's audible or the fact that it fluctuates...or some other consequence?

Thanks, Rex!

After consulting with Ernie (Subaruguru) I installed two dedicated lines, one using 12AWG Teflon-insulated Belden wire, and one using 10AWG Romex (for my amps). The difference was not subtle. Before I installed the dedicated lines, I had my entire system powered using the existing, shared line. My amps had been bordering on clipping when trying to drive my Thiel CS3.6's to even moderate levels. After giving them a dedicated line, I never saw the distortion lights flicker even once, even at loder listening levels.

The nice thing about the Belden wire Ernie sells is that if you have any left over, you can make some very nice power cords out of it.

Good luck, Tom.