Main vs. sub panel for dedicated lines

How far away from the main panel is the listening room and the two bedrooms and bathroom? The only reasons for a subpanel is to limit the voltage drop over long distances, or to group together outlets in a common area so as not to overstuff the main panel (i.e. a garage woodworking shop with numerous 240V circuits for power tool motors).

To give you a perspective: a #12 branch line carrying a load of 10 amps can be run up to 75 feet to keep the voltage drop under 2.5%. That is a lot of amps. If you go with #10 wires, then you can go up to 125 feet for a 2.5% voltage drop.

Since you have a dedicated service drop for the second structure, I see no reason for a subpanel with only three audio lines, one GFI bathroom circuit and one or two AFI bedroom circuits. Unless it is quite a big house.

Mike, if you're using 10 gauge wire the breakers should be 20A. There's no reason to use one 15 and one 20A. 
If you use 10/2 Romex, you would use two 20A receptacles for your audio.

As stated before, use a subpanel for audio. Main 200A panel will have high-current draw appliances, lighting, and household devices.
Each panel will have an 8' ground rod, check with electrician for code.

Each panel will have an 8’ ground rod, check with electrician for code.

If the sub panel is located in the same building as the main service panel a ground rod is not required for the sub panel. Yes per the NEC a driven ground rod can be connected to the equipment ground bar in the sub panel. (2017 NEC 250.54) I would not recommend it though.

If the sub panel is located in another building, such as a detached garage, then a new grounding electrode is required and bonded to the equipment ground bar/ panel enclosure/feeder equipment grounding conductor. (Feeder neutral conductor is never bonded to ground in a sub panel. Neutral conductor/ bar shall be isolated from ground/ panel enclosure.)

Minimum required number of driven ground rods for the main service panel technically is one, * IF *, the ground rod to soil resistance is 25 ohms or less.
How can the electrician know for sure if it is 25 ohms or less? With testing equipment that is made to test it. If an electrical inspector sees only one ground he will ask to see a print out of the test. It is cheaper by far for the electrician to just drive two ground rods and be done with it.

mesch, makes absolutely do difference. In order to isolate your system from everything else your would have to have the power company install a separate high voltage transformer on your lawn and run a second main from that to run the system, just a bit absurd from a financial standpoint.
For good equipment it does not matter. I have a three phase workshop in my bottom floor. I can run the phase converted, stop and start machinery and you can hear the tiniest click in the system. All of this is running off the same main. The power company did make me get my own transformer but this was to isolate my neighbors from me, not me from myself.

Just to add to why a sub panel(s) may be needed.


For one because a 42 circuit main panel (If main breaker is in the panel 40 spaces/circuits for branch circuits) isn’t enough spaces/circuits for all the circuits need for the home. I have a sub panel for just that reason. It is mounted beside the main panel.
(42 circuit used to be the max for an electrical panel. That was changed a few NEC code cycles back. There is not any limit now to the number of spaces/circuits in a panel enclosure.)


Sometimes a sub panel is used because of the distances lengths of home run branch circuits. Not for just branch circuit voltage drop. Considered is material and labor, it is cheaper to install a sub panel than run several branch circuit home runs back to one panel. And again one panel was not big enough.

Another reason for more than one panel is the size of the electrical service.
Two main disconnects are located on the outside of the house by the electric meter, (Often in a common enclosure with the meter socket). Each main breaker will feed a sub panel. They both might be side by side or separated from one another for splitting up branch circuit home runs.

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