It shouldn't be like that. If all the Remote Power Cables are in place all you do is select the "power on" menu on the control processor and it should sequence the entire room up in order so that you don't trip the breakers. I seem to remember it took around 20 minutes so some folks would try and short circuit the process. Rather amazing really to hear the room come to life after a full power down..
They didn't show very much of the actual process, just some preliminaries with the power management equipment. Nothing of the walking the room and ensuring all the switches are in the correct positions and that things power up as expected. Then starting the mainframe from the service processor, which could take many steps before you actually IPLed a logical partition (which corresponds to booting smaller systems). It always boggled my mind that more of the boot process wasn't automated on older systems.