The electrical system consists of an electrical management system (EMS), an AC and DC electrical systems. It supplies and controls the AC and DC electrical power to the aircraft.

The electrical management system control display units (EMS CDUs) provide for system distribution control as well as remote circuit breaker status. The primary AC power supply is a variable frequency system, powered by four engine-driven variable frequency generators (VFGs). An auxiliary generator, located on the auxiliary power unit, operates at a fixed frequency.

In the event of an emergency in flight, a ram air turbine AC generator is provided. An external AC power source can be connected to provide power to the aircraft systems on the ground.

The four engine-driven variable frequency generators (VFGs), the auxiliary generator and the external AC power source outputs are supplied to the AC power center (ACPC), which distributes the power to the aircraft subsystems. The ram air turbine AC generator output is supplied to the cockpit circuit breaker panel (CCBP), which distributes the power to the aircraft essential systems.

The DC electrical system consists of four transformer rectifier units (TRUs) for normal power distribution and two nicad batteries for initial system power-up, APU starting and emergency power. An external DC power source can be connected to provide limited power to the DC electrical system on the ground.The TRUs receive power from the AC system, which is transformed and rectified into DC power. The TRUs DC output is supplied to the DC power center (DCPC), which distributes the power to four secondary power distribution assemblies (SPDAs). The SPDAs distribute power to the aircraft subsystems.

There are four junction boxes. They provide an ARINC data bus interconnection point and distribution of electrical power to aircraft system loads.

A DC emergency override system, consisting of electrical hardware, allows two of the TRUs to feed directly the SPDAs. By activating the system,the DCPC is bypassed during emergency conditions.

Cockpit interface with the electrical system consists of an electrical control panel, engine indication and crew alerting system (EICAS), electrical management system control display units (EMS CDUs), and ram air turbine manual release handle. The electrical control panel is equipped with a battery master switch and pushbutton annunciators (PBAs), which provide system control and status information.

An AC power receptacle and an aft service control panel are provided to connect an external AC power source to the aircraft for maintenance purposes. An external DC receptacle, located on the underside belly behind the aft equipment compartment, allows an external DC power source to be connected to the aircraft for APU start and limited use of the DC system.

Both AC and DC electrical systems can be monitored by the crew using the EICAS primary and synoptic pages.

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