Guardian 4389 Diagnostic Repair Manual page 53

SECTION 3.2
OPERATIONAL ANALYSIS
If utility source voltage should drop below a preset value, the generator circuit board will sense the dropout. That
circuit board will then initiate generator cranking and startup after a time delay circuit times out.
Figure 3 is a schematic representation of the transfer switch with generator power available, waiting to transfer.
Generator voltage available E1, E2.
Circuit board action holding Wire 23 open to ground.
Power available to standby coil C2, upon closure of TR, normally open contacts (9 & 6) will close and initiate a
transfer.
Page 3.2-3
UTILITY SOURCE VOLTAGE FAILURE
Figure 3. Generator Power Available, Waiting to Transfer.
V-TYPE PREPACKAGED
PART 3
TRANSFER SWITCHES