B737 Ground Power and Bus Switching Panel

GEN/APU PNL
P5 FWD OVERHEAD

Ground Power Available (GRD POWER AVAILABLE) Light

  • Illuminated (blue): Ground power is connected and meets airplane power quality standards.

Ground Power (GRD PWR) Switch

  • Three-position switch, spring-loaded to neutral
    • OFF: Disconnects ground power from AC transfer buses.
    • ON: If momentarily moved to ON position and ground power is available:
      • Removes previously connected power from AC transfer buses
      • Connects ground power to AC transfer buses if power quality is correct

TRANSFER BUS OFF Lights

  • Illuminated (amber): Indicates related transfer bus is not powered.

SOURCE OFF Lights

  • Illuminated (amber):
    • No source has been manually selected to power the related transfer bus, or
    • The manually selected source has been disconnected
    • Note: If a source has been selected to power the opposite transfer bus, both transfer buses are powered.

Generator Off Bus (GEN OFF BUS) Lights

  • Illuminated (blue): Indicates IDG is not supplying power to the related transfer bus.

Generator (GEN) Switches

  • Three-position switch, spring-loaded to neutral
    • OFF: Disconnects IDG from related AC transfer bus by opening the generator circuit breaker.
    • ON: Connects IDG to related AC transfer bus by disconnecting the previous power source and closing the generator circuit breaker.

BUS TRANSFER Switch

  • AUTO (guarded position):
    • BTBs operate automatically to maintain power to AC transfer buses from any operating generator or external power
    • DC cross tie relay automatically provides normal or isolated operation as required
  • OFF:
    • Isolates AC transfer bus 1 from AC transfer bus 2 if one IDG is supplying power to both AC transfer buses
    • DC cross tie relay opens to isolate DC bus 1 from DC bus 2
    • Inhibits TR3 input from connecting to AC transfer bus 1

APU Generator Off Bus (GEN OFF BUS) Light

  • Illuminated (blue): Indicates APU is running and not powering a bus.

APU Generator (GEN) Switches

  • Three-position switch, spring-loaded to neutral
    • OFF:
      • APU generator powering both AC transfer buses
      • Moving a single APU GEN switch to OFF illuminates the related SOURCE OFF light. APU continues to power AC transfer buses
      • Subsequently moving the other APU GEN switch to OFF disconnects APU generator from tie bus and removes APU power from AC transfer buses
      • APU generator powering one AC transfer bus; IDG powering one AC transfer bus
      • Moving the related APU GEN switch to OFF disconnects APU generator from tie bus and AC transfer bus. IDG powers AC transfer buses
    • ON:
      • Neither AC transfer bus powered by IDG: Moving a single APU GEN switch to ON:
        • Connects both AC transfer buses to the APU generator
        • Disconnects external power, if connected
        • Opposite SOURCE OFF light illuminates until the other APU GEN switch is moved to ON
      • Both AC transfer buses powered by IDGs: Moving an APU GEN switch to ON:
        • Powers the related AC transfer bus from the APU generator
        • The other AC transfer bus continues to receive power from the IDG

Other Electrical Panels:
Generator Drive and Standby Power Panel
AC/DC Metering Panel