I'm going to jump into this rabbit hole by relating my, ultimately positive experiences. When I bought my Long Island 1895 house, its original electrical service was 30A 110V panel with 4 15A fuses to a small number of circuits. It had been replaced with a 60A, 240V service (again with fuses) and several more circuits run, including one for an electric clothes dryer, a hot water heater, and a room air conditioner (the only circuit with Romex). Like the OP, I decided I needed more circuits, and would prefer a breaker box rather than a fuse box. I investigated having a new service run with new meter and put in a 200A breaker box myself but the restrictions were so great, I gave up on that idea. I would have had the POCO come and pull the breaker (a 2 week wait for that service), the install my new meter pan and panel, have it inspected (another 2-4 week wait), then have the POCO put in the new meter. I couldn't deal with all those delays, so I decided to go the "subpanel" route: I purchased a 40 slot load center and mounted it next to the old fuse box. I then ran 4 Ga wires from the old fuse box to the new breaker box and started moving circuits. When I had finished moving all the old circuits, I essentially abandoned the old box, using only the 60A cartridge fuses as primary protection. Finally I called a licensed electrician come in and replace the meter pan, meter, and reconnect the new panel. It took him about 2 hours to accomplish all that. While I was operating my new panel from the old 60A service, I never blew the main breaker. But that's understandable, since I had essentially no high current appliances, especially after I replaced my clothes dryer and domestic hot water heater with gas appliances. So I accomplished my original goal: more breakers to run more services, but not use significantly more power. On a side note, there was only one 15A circuit for the entire second floor; that must have been left over from the original wiring. Very difficult to run new wiring from the basement to the second floor, so I managed to run 3/4" EMT from the basement to the third floor (attic) and put in a 50A subpanel there, and run all the necessary lighting and receptacle circuits circuits from it. End of rabbit hole!

So, for the folks who are running their central AC on a small generator, there are some things to consider so you don’t damage your ac. Just because it’s working doesn’t mean it’s not harming your central ac. 1st you need to have a quick reading voltage meter your typical cheapie can’t read ms long voltage changes. What your looking for is when your ac starts what is the instantaneous voltage drop. If your seeing under 208V when starting your ac, your accelerating wear on your motor windings on the compressor. Your compressor takes a certain amount of wattage which varies depending on temperature. If your ac says 90lra at 208v you need 18,720 starting watts, to start the ac without a voltage drop. If your generator can’t supply the needed power, you’ll slow the engine down and bog the generator causing its output voltage to drop, and say it’s outputting only 185v starting the ac. That means your ac is now drawing 18720/185=101 amps, and for a longer period of time. at low voltage the ac will take longer to start, heating the motor winding on your ac significantly more, once the insulation degrade or the wiring melts in the ac your compressor is done, So it’s not that it can’t be done, but it will wear your compressor a lot more quickly. Also if your ac doesnt sound the same while running it’s because the motor is vibrating more due to a highly distorted ac wave form or high THD from the generator. This extra vibration will wear the compressor more quickly and if bad enough destroy the motor. So some things to keep in mind when running a central ac on a generator. something highly recommended for small generators is leave the ac running all the time to reduce starts which damage the motors and or install a soft start kit to reduce LRA. If the ac is noisy on generator power get a different generator with a low thd, make sure it’s grounded properly if needed and consider upgrading your ac run capacitor to a 440v. Real bottom line, a cheap generator can run a very expensive ac. But if it kills your ac you didn’t really save money by buying a cheap generator.

OK, Ronnatalie - What I was calling joists are the ceiling joists. Because this is a prefabricated shed, the ceiling joists are 2X4s, not 2X6s. Let me start again, please. The service main panel is a 200 Amp, Challenger box. Breakers 29 & 30 are double pole 30 Amp breakers. These two breakers feed a sub panel using 12/3 wire. Black to a hot lug, red to a hot lug, white to neutral bus and ground to ground bus. My current plan call for an R&R of the 30 amp breaker in favor of a double pole 20 amp breaker. The sub panel hold four breakers, At present two of the breakers are 30 amp breakers that I'm going to replace with 20 Amp breakers. The other is a double 20 amp breaker, it services all the 110/120 for this room. I'm going to replace that breaker with two individual 20 amp breakers. There should be no 30 amp circuits needed. Breaker #1 will be a dedicated double receptacle for my laser printer. Breaker # 2 will service the right side of the shed receptacles. Breaker # 4 Will service the left half of the shed receptacles. Back at Service Main, Breakers 31 and 32 currently a double breaker 30 Amp. feeds a baseboard 220 heater. The run is made with 12/2 cable. Black goes to Breaker 31 and white / with black tape goes to breaker 32. I'm planning on removing the double breaker and replacing it with a single 20 breaker. Removing the black tape from both ends of the white wire. Next I'll install a double receptacle to function as a dedicated line for the window AC and the ceiling lights. Sorry if I confused you.

I was looking at wiring diagrams for prewired transfer switches and they do exactly what I want to do. Take the hot wire off the breaker and connect it to the transfer switch which contains a breaker but they leave the neutrals and grounds where they were. So are they also wrong? I am not aware of the derating current when using a conduit but I suppose it has to do with "back emf" or eddy currents. I will have less than 15 feet of conduit and thought it easier & neater than running 12 NM cables. However I can just run 12 black(hot), 12 white(neutral) & 12 green (ground) in my 1 1/4 conduit. Or are you suggesting 3 separate conduits for each type of run?