Guardian 4721 Repair Manual page 78

SECTION 4.2
OPERATIONAL ANALYSIS
CIRCUIT CONDITION- INITIAL RETRANSFER BACK TO UTILITY
• When the "return to utility timer" times out (about 10 seconds), control board action will open the Wire 23 circuit
to ground.
• With Wire 23 circuit open, the transfer relay (TR) will de-energize. The relay's normally-closed contacts will
close.
• Utility source power is now delivered to the main contacts actuating coil (C), via Wires N1/N2, the closed TR
contacts, transfer mechanism terminals A1/A2, limit switches XA1/XB1, and the bridge rectifier.
• Actuating coil (C) energizes and the main contacts are pulled to their "Neutral" position. The main contacts will
remain at "Neutral" ("Load" disconnect from both power supplies) as long as actuating coil (C) remains ener-
gized.
Page 74
DC CONTROL
PART 4
LIQUID COOLED
ENGINE UNITS