P/N 13999-002 Info Manual 7-51
Cirrus Design Section 7
SR20 Airplane Description
Power Distribution
Power distribution for the SR20 consists of the electrical power bus in
the Master Control Unit (MCU), Main Buses, Essential and Non-
Essential buses in the circuit breaker panel, as well as associated
fuses, circuit breakers and switches. The main power buses (Main Bus
1 and Main Bus 2) and the Non-Essential equipment bus receive
power from the power generation system through 25-amp feeder bus
fuses or circuit breakers located in the Master Control Unit (MCU). The
Essential power bus is powered from Main Bus 1 and Main Bus 2 from
the Essential 1 and Essential 2 circuit breakers through a network of
diodes. The Non-Essential avionics bus and the Essential avionics bus
are powered from Main Bus 1 and the Essential power bus
respectively through the associated Avionics circuit breakers provided
the AVIONICS POWER switch is ON. Avionics loads on the avionics
buses can be shed by pulling the associated Avionics circuit breaker.
BAT & ALT Master Switches
The rocker type electrical system MASTER switches are ON in the up
position and off in the down position. The right switch, labeled BAT,
controls all electrical power to the airplane. The left switch, labeled
ALT, controls the alternator.
Normally, both master switches will be ON. However, the BAT switch
can be turned on separately to check equipment while on the ground.
To check or use avionics equipment or radios while on the ground, the
avionics power switch must also be turned on. Positioning the ALT
switch to the off position isolates the alternator from the electrical
system and the entire electrical load is placed on the battery.
• Note •
Continued operation with the alternator switched off will
reduce battery power low enough to open the battery relay,
remove power from the alternator field, and prevent alternator
restart.
September 2011
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