Moonguy:
House wiring these days is safeguarded by circuit breakers instead of fuses. They have ratings of 10 to 30 and sometimes 50 amps. When the current draw on the wire connected to a given breaker exceeds the rating of the breaker for a set amount of time, the breaker trips and shuts off the current to that circuit. When homes are wired, consideration is given to the likely draw a given room might need. Kitchens with large electric ovens get breakers with high ratings and usually have wiring of heavy guage. Ten or twelve guage is common for large breakers. Bedrooms and hallways get 15 amp breakers because the loads are mostly lighting and light duty stuff, while a laundry room with an electric dryer and washer would get a breaker of a much higher rating. Important to consider is the overall wattage a wall socket and a single circuit can handle. A circuit with a 15 amp breaker is usually good for 2500 watts or so. Twenty amp breakers much more. When wiring a home theater or dedicated room, dedicated lines with their own breakers for individual components are very beneficial. Not only are ground loops kept to a minimum, but your system can draw much higher wattages from the breaker box than your system might otherwise be able to plugged into all the outlets in the listening room. It's common for several outlets in a room to be all on the same circuit. All those outlets would be on ONE breaker, greatly limiting the available current for your amps, video display, powered subs, and everything else in the system. A twenty amp circuit (line) is a circuit with a twenty amp breaker, heavy guage wiring to handle the current draw, and sometimes a twenty amp wall outlet in the room. True twenty amp outlets are a different configuration than a 15amp outlet. This convention can keep a heavy draw appliance from being accidently plugged into a wall outlet that might not be able to supply the current flow that unit would need. Commonly though, a lot of 20 amp outlets allow both standard 15 amp and the 20 amp plugs to fit. Check this thread on Audioholics about questions similiar to yours:
http://forums.audioholics.com/forums/archive/index.php/t-3266.html%22%3Edebate%3C/t-14420.html
