Instructions to electrician about dedicated line

What if you ever change amps? I put in a whole house surge protector as well. It prevents outside problems from interfering but will not protect you from inside trouble(ie feedback from your a/c compressor). For that reason, I also use a line conditioner/surge protector at the unit. I like using GFIs also.

The answer to the, "Why 15A or 20A circuits" is really a code question. The smallest wiring allowed by the NEC for a power circuit in a residence is 14 gauge with 12 gauge being common. Since a 14 gauge wire will carry 15A, it's typical to install a 15A breaker on a 14 gauge circuit. Likewise with 12 gauge and 20A breakers.

Sean's (and others') suggestion to use 10 gauge wire in a 20A circuit is to reduce voltage drop in that circuit. 10 Gauge wire will carry 30A and could have a 30A breaker installed in the circuit. From a power delivery standpoint (up to 20A, of course), this circuit won't be any different with a 20A or 30A breaker installed. However, one might be able to find a higher quality 20A breaker for the same price as a regular 30A breaker.

The thing to remember is that wire is sized to carry a load and the breaker is sized to protect the wire, not the other way around. So, while it's OK to install a 20A breaker in a circuit wired with 10 gauge wire (your electrician will look at you funny, but what does he know?), it is NOT good (or legal) to install a 20A breaker on a circuit wired with 14 Gauge wire.

Macdonj, thanks for clarifying why i stated what i did. In that respect, you were right on the money. However, i would like to add that i don't personally feel that 10 gauge is sufficient for 30 amp service. Regardless of what most "professionals" will tell you, 10 gauge will produce a very noticeable voltage drop under a 30 amp load if it is anything more than a few feet long. I have measured sizable voltage drops using 8 gauge at lengths of under 20 feet while trying to pull 30 - 35 amps through it. As such, i would consider 10 gauge "adequate" for a 20 amp load using the normal length runs that one might find in a house. 12 gauge should be considered minimum for a 15 amp circuit. That is, if one is looking to reduce series resistance / voltage sag to a minimum.

As i've mentioned before, i'm simply sharing / passing on my personal point of view based on the experiences that i've had. As such, my comments are worth just slightly less than what you paid for them : ) Sean
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Bear: While i can understand your thoughts about using one BIG isolation transformer to feed the A/V breaker box for sake of simplicity, what are your thoughts on using multiple smaller ( 15 - 20 amps each ) yet identical transformers wired in parallel ? Sean
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Sure, Sean, that's pretty good in principle - but you have to think about what happens to the grounds too...

Also, are you saying multiple 240vac lines, or 120vac lines?
One of the advantages of the 240-->120 stepdown is that it makes for a way stiffer line in general.

I'd be worried about voltage drops over multiple lines being different, and causing a ground problem on a 120v-->120v iso set up. With 240vac you have two hots and a dedicated ground there... dunno, I haven't thought this through all the way...