OPERATIONS MANUAL

Electrical
Battery Busses and Hot Battery Busses:
The battery busses are powered by their respective hot battery busses or
by DC bus 3 when available. The battery switch on the overhead panel
can disconnect the battery busses from the hot battery busses. Battery
chargers stabilize the power on the hot battery busses.
Towing Power Bus:
The towing power bus powers only equipment that is essential for towing
operations. It is powered by the main battery when the standby power
selector on the overhead panel is set to OFF and the towing power switch
on the maintenance panel is set to BATTERY.
Utility Busses
and Galley Busses:
Every AC bus powers an associated utility bus and—on passenger and
combi aircraft—a galley bus. The utility and galley busses supply less
important devices that can be disconnected when not enough power is
available on the aircraft. The disconnection and reconnection is managed
by electrical load control units (ELCUs).
Transfer Busses:
Some of the more important devices are powered through transfer
busses which use a backup power source when the primary source fails.
• The captain’s transfer bus normally uses AC bus 3; and if this fails,
AC bus 1.
• The first officer’s transfer bus normally uses AC bus 2; and if this
fails, AC bus 1.
The control system senses the voltage of the respective primary source
and will automatically transfer to the backup source when a fault is
detected. The control system is powered by DC bus 1; if DC bus 1 is
unpowered, the transfer busses will not switch to AC bus 1.
— Page 187 —
For preview only. Not for sale. Many pages are intentionally removed.