Textron 172R180HP, Pilot Operating Handbook

Page: 221 / 396

CESSNA SECTION 7
AIRPLANE & SYSTEMS DESCRIPTION MODEL 172R (180 HP)
MASTER SWITCH
The master switch is a split rocker-type switch labeled MASTER.I
and is ON in the up position and off in the down position. The right
half of the switch, labeled BAT, controls the battery power to the
airplane. The left half, labeled ALT, controls the alternator.
AcAur10N
PRIOR TO TURNING THE MASTER SWITCH ON
OR OFF, STARTING THE ENGINE OR APPLYING
AN EXTERNAL POWER SOURCE, THE AVIONICS
I
MASTER SWITCH SHOULD BE TURNED OFF TO
PREVENT ANY HARMFUL TRANSIENT VOLTAGE
FROM DAMAGING THE AVIONICS EQUIPMENT.
Normally, both sides of the master switch should be used
simultaneously; however, the BAT side of the switch could 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
master switch must also be turned on. The ALT side of the switch.I
when placed in the off position, removes the alternator from the
electrical system. With this switch in the off position, the entire
electrical load is placed on the battery. Continued operation with the
alternator switch in the off position will reduce battery power low
enough to open the battery contactor, remove power from the
alternator field, and prevent alternator restart.
Oct 4/01
7-33