"What I was tring to say tho was technically you can not get 20 amps from each plug at the same time. That is impossible. The duplex is only good for 20 amps" Yes you can get 20 amps from each outlet at the same time. The upper and lower receptacle are connected by the metal tabs on the side of the outlet, cut those metal tabs and now you can install a 20 amp circuit on the top, and a 20 amp circuit on the bottom recpetacle. By doing this one could now run their 20 amp saw from the top receptacle, and their 20 amp heater from the bottom recepetacle. This is exactly why it is called a "duplex receptacle" as others have mentioned. It is called a "duplex" because it has (2) 20 amp receptacles on it.

An update on where things ended up... The electrician advised me that I have 100amps at 600v/3 phase which translates to 300amps at 110v. So I've got lots of power. He's going to run a sub-panel from my breaker panel to my dimmers, and include 16-24 outlet plugs at 20amps/110v and a couple of 220v'ers. He advised that we don't need to turn of the master power to the master breaker, and can leave the rental units with their power on while the work takes place. He also informed me something fascinating about the dimmer packs. I had thought that if I have a 500 watt light plugged in, but I dim it to 10%, I would only be using 50 watts of power. Apparently this is not the case, and I continue to draw the full 500 watts. However only 50 watts goes to the light and the rest gets drawn by the dimmer pack. No wonder my electricity bill is so damn high. In total he's advised me it will be one full day's work. S

Thanks for the replies. @ronnatalie 240V circuits it seems may not required except for some equipment which can draw in excess of 2200W (don't have any such equipment now) are explicitly designed to work only for 240V (max safe limit for 120V 20amp circuit would be around 2000W?) @joww9 thanks for the suggestion on independent ground. Will discuss that with the builder. I guess my question about 50hz shows how clueless I am :) I am guessing its not possible to do 50hz without some additional transformer etc. My primitive understanding is that 50 vs 60 hz may not be important as most equipment are able to tolerate that variation in freq. I guess I will go with one 20amp line for the rooms where dry wall is being put up now should be able to add additional 20amp outlets when we finish the basement later?

For the combination of general lighting and general use receptacles the code does limit, in a round about way, a 15amp circuit to 600 square feet of dwelling. While at the same time there would be no limit on the number of general use receptacles you could install on this circuit. This may not always be a practacle limit and could result in tripped breakers on a regular basis, but the code is only concerned with the safety of an installation. The practicality or convenience of the installation is a design issue.