Diamond Aircraft DA 40 NG Airplane Maintenance Manual page 518

Electrical Power
(5) ECU Bus
The ECU bus is located at the circuit breakers. The ECU bus has power when the any one of
the following are connected to the ECU bus:
)
The main battery.
)
External power.
)
The alternator.
The ECU bus provides power for Engine Control Unit A (ECU A) and ECU B and their fuel
pumps. Circuit-breakers protect each circuit.
The ECU B and its fuel pump is connected to the ECU bus via a diode and a fuse. The ECU
backup battery is also connected to ECU B and its fuel pump.
(6) Main Bus
The main bus provides power for the consumers. Each consumer has a circuit breaker to
protect the circuit. The main bus also connects to the switch contact of the starter relay. A
circuit-breaker protects the supply to the relay.
(7) Power Relay
The power relay connects the battery bus in the instrument panel to the main bus. The essential
bus switch controls the power relay.
(8) Essential Tie Relay
In the usual (de-energized) condition, the essential tie relay connects the main bus to the
essential bus.
In the emergency (energized) condition, the essential tie relay connects the battery bus in the
instrument panel to the essential bus.
The essential bus switch controls the essential tie relay.
Page 8
24-00-00
01 Sep 2017
AIRCRAFT
DA 40 NG AMM
Doc # 6.02.15
Rev. 3