What about those gadgets the utility companies are pushing that allow them to remotely turn off your heating, AC and hot water heater?
When the utility is able to set up interrupt-able service to your AC (or hot water heater), that circuit is separate from the main circuit feeding current to your house. That circuit will have a remotely re-closeable breaker in the substation, or an extra gadget at your house. We had such service in Sacramento in 1986-1987. The utility company only needs to engage the interrupt-able service provision during peak loads on that part of the distribution system — peaks last only a few hours at most. The tactic is only useful when a bunch of folks opt for the alternate circuit to the AC (or hot water). The governing PUC forces utilities to have installed available capacity for well over 100% of estimated peak load. Thus, there is no incentive for the utility to shut off service except in extreme circumstances. Responses to extreme circumstances would otherwise require amperage reduction (brownout — damaging equipment by overheating) or selective blackouts.