MAIN SERVICE PANNEL
If you add up all the breakers in your main service panel, it is normal for the total to exceed the rated capacity of the box. That is because it's assumed that you will not be using all circuits at their full capacity at the same time. When the house is built, a load calculation is done on all the appliances, AC, outlets and lighting loads that might be in use at the same time to determine the size the main panel.
WIRE
The breaker size and wire gauge for each circuit are determined by the type of load. The rule of thumb is that nominal load should not exceed 80% of capacity. Therefore, for convenience outlets you typically run 12 awg wire capable of 20 amps even if the breaker and receptacles are rated at only 15 amps. It's not uncommon to run 12 awg wire to a switch box with multiple 300w/600w dimmers then run 14 awg on the switch leg from each dimmer to the lighting loads.
THNN solid core wire will carry a greater maximum amperage than stranded wire. It's always easier to run 12 awg wire and limit the circuit to 15 amps with the breaker and receptacle, than to decide later you want 20 amps and re-pull wire through a crowded conduit or Romex through walls under sealed drywall. Your time and labor are much more expensive than the cost difference between 12 and 14 AWG.
BREAKERS
Think of electricity like water. It comes in from the street on two hot wires (phase one & phase two) and then returns to the source through one common wire. The local utility sends a 110v pulse on phase one, then a 110v pulse on phase two, then back to 110v on phase one, and so on. In your Main service panel there are two sets of copper rails for phase one and phase two. A 110v "single-pole" breaker will snap onto only one rail, a 220v "double-pole" breaker will snap onto both rails.
Breakers come in different configurations: (1) Half size 1/2" single pole , (2) Full size 1" single pole or double pole (3) Twin 1" two single pole, and (4) Quad size 2" four single, two double pole or a combination thereof. When you add a circuit, you simply pull out one or more Full size breakers and replace them with Twins or Quads to free up one or more unoccupied terminals.
PHASE
Phase is important to keep track of because typically you will run three wires (two hots and a common) from the main panel to a given location. Each hot wire is on a different phase and they share the common wire with the current alternating between them. if you get your commons mixed up at the end location, you can have two hots trying to drain through the same common and overheat the common wire. You can also get voltage feeding back through dimmers or an adjacent load if you don't keep track of which common goes to which load.
Typically electricians run black for phase one, red for phase two, and white for the common to keep track of phases at the end location, using colored wires to differentiate switch legs or branch circuits. Typically, I will run all my hots and commons in red, black and white to a junction box in the Theater area, then make it up with colored wire pulled to the various receptacles.
AUDIO
For audio equipment, especially power hungry amplifiers, I always run 12 awg, with 20 amp breakers and 20 amp receptacles. There are expensive audiophile receptacles from PS Audio and others, but a standard hospital grade outlet from your local electrical supply is more than comparable.
When running multiple amplifiers in home theater, it's important to do a load calculation and distribute the amplifiers over a sufficient number of circuits. You can get the maximum current draw of each amplifier from the specifications in the owners manual or by calling the manufacturer's technical support. Remember that the rule of thumb is 80% load to capacity. A receptacle wired for 20a/110v is rated for 2200va, so two amplifiers rated at 850va each will just about use up one 20 amp circuit.
Many high power multichannel amplifiers can easily take up a 20 amp circuit on their own. Multiple subs in an installation can also require one or more circuits (although the newer class D amps may use less power than a traditional class a/b amp). If possible, keep the electronics and video on a separate circuit so that they are not effected by a surge in demand from multiple amplifiers during demanding special effects.
GROUND LOOPS
Ground loops occur whenever the grounding potential one receptacle location is significantly stronger than another. They can be difficult to track down and aggravating to eliminate. To preempt ground loops when I pull wire for a theater, I usually pull a 12 awg green ground wire along with my hots and commons (or the bare copper ground wire in Romex) from the receptacles in the theater room to the Theater central junction box. From there I wire nut them to a 10 awg stranded green wire back to the ground block in the main panel. Most main panels have a heavy gauge wire connecting their grounding block directly to a nearby long copper rod hammered deep into the ground. This guarantees that the grounding potential for all receptacles is greatest at one common point at the theater junction box.
