What exactly is a 20 amp dedicated line?


My electrician was over this morning installing Porter ports. I had him install 20 amp dedicated lines a while ago. The wall outlets have two places for plugs. It was my impression that a 20 amp line was a separate line for each plug. However, he stated that a 20 amp line was for the double plug instead of the single plug. Luckily I only have one amp plugged into each double outlet. However, If I decided to plug two amps into an outlet with two plugs, wouldn't it negate the 20 amp line? Your comments would be greatly appreciated.
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Jea48, do you know if it's Code to run a single 220v romex line consisting of 2 hots, 1 neutral and 1 ground into a single receptical box, with each hot powering a separate receptical and the single neutral and ground doing double duty for the two recepticals? I assume that each hot would be connected to a separate breaker in the fuse box. If Code, this would be an efficient way to run 2 dedicated lines with one romex run.

Of course, the polarity of each receptical would be inverse to the other if powered by the 2 hots.
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.