What exactly is a 20 amp dedicated line?

WOW! I think that I bit off more than I can chew from the responses above. Thank you very much for all of the information.

Bifwynne,

Yes, it is called a multi wire branch circuit. (Two 120V separate circuits.) Not two dedicated circuits....

Not so good for audio equipment that is connected together by ics though.

In 2008 NEC required that multi wire branch circuits must be fed by a multi pole branch circuit breaker. Too many electricians were being killed from an open neutral....

Thanks Jea48 for the info. Please clarify a couple of points you made. First, is the NEC the National Electricans Code?

Second, if a multi wire branch circuit is set up in the manner I described above, please explain how a multi pole branch circuit breaker works. For example, if each hot energizes a separate receptical, is it possible that a short or overload of one receptical fed by one hot would NOT trip the breaker for the other circuit fed by the other hot? If such is the case, isn't that the practical equivalent of 2 dedicated lines?

BTW, for the benefit of others, if a multi branch circuit is legal under applicable Codes and safe, the reason that it could mess up a stereo system is because the AC current is alternating in opposite phases in each hot. That is how 220 v is obtained. I know this because I was an electrician's assistant when I was in college back in 1970. I remember that a 220 v shock can knock your fillings out -- and if that's all that happens, you're da*n lucky.

However, as far as the specific electronic consequence of mixing and matching different phase circuits in stereo gear is concerned, I'll leave that discussion to the electronics techies out there if they think it's worth a comment or two.

Thanks again.

A dedicated line starts from the electrical panel and ends at only one location. The outlet can be any configuration, single, dual or quad.
Most outlets in your house say in your livingroom are daisy chained and lead to more than one outlet in differant locations.

....

is the NEC the National Electrical Code?

Yes.

Second, if a multi wire branch circuit is set up in the manner I described above, please explain how a multi pole branch circuit breaker works.

The multi pole breaker has the function of controlling all of the circuits of a multi wire branch circuit simultaneously. NEC Code changes mandated that all circuits of a multi wire branch must be de-energized by a one handle action. All on or all off. Pre-code change, individual single pole breakers were used. It is a safety thing for an electrician or maintenance person that may be working on one or more of the circuits of the multi wire branch circuit.

In commercial and industrial buildings 3 phase 4 wire multi wire branch circuits are quite common.
(3) hots, (1) neutral, and (1) equipment ground.

For example, if each hot energizes a separate receptical, is it possible that a short or overload of one receptical fed by one hot would NOT trip the breaker for the other circuit fed by the other hot?

That is true where a single pole breaker is used for each circuit of a multi wire branch circuit.
That is not the case when a multi pole breaker is used. In the case of a 3ph 4 wire multi wire branch circuit a 3 pole breaker must be used for the overcurrent protection of the branch circuit.

If one of the circuits of the three was overloaded the breaker will trip open and take the other two circuits with it.

Multi wire branch circuits are a thing of the past now..... At least in jurisditions that approved that part of NEC.