As befits the world's first more-electric airliner, the 787's electrical system generates almost 1.5 megawatts, or enough to power about 400 homes. The system replaces conventional engine bleed air to electrically power engine start, pressurization and wing ice protection. It also replaces hydraulic power for stabilizer trim and wheel brakes while supplying the traditional electrically powered systems. Six generators, two 250 kva per engine, and two 225 kva on the auxiliary power unit, all operate at 235-volt alternating current (Vac). The generators are connected to the engine gearboxes and operate at a variable frequency (360-800 hz.). The system incorporates two electrical/electronics (E/E) bays, one forward and one aft, as well as several remote power distribution units (RPDUs) which act like substations on a power grid. The majority of systems, being either 115Vac or 28Vdc, are supported by the forward E/E bay and RPDUs.