Guardian 4721, Repair Manual

Page: 49 / 115

“V-TYPE” PREPACKAGED
TRANSFER SWITCHES
SECTION 3.2
OPERATIONAL ANALYSIS
PART 3
Page 45
UTILITY SOURCE VOLTAGE DROPOUT
If utility source voltage should drop below a preset value, the generator’s control board will sense the dropout.
That circuit board will then initiate generator cranking and startup after a time delay circuit times out.
TRANSFER TO STANDBY
The generator’s control board delivers 12 volts DC to the transfer relay, via terminal 194 and back to the circuit
board via terminal 23. However, circuit board action holds the Wire No. 23 circuit open and the transfer relay
remains de-energized. On generator startup, an “engine warm-up timer” on the generator’s control board starts
timing. When that timer has timed out, control board action completes the Wire No. 23 circuit to ground. The trans-
fer relay then energizes, its normally-open contacts close, and standby source voltage is delivered to the standby
closing coil via Wires No. E1 and E2, the transfer relay (TR) contacts, limit switch (XB1), Wire “B”. and a bridge
rectifier. The standby closing coil energizes and the main contacts actuate to their “Standby” side.
Figure 2. Circuit Condition - Transfer to Standby
TR RELAY, TRANSFER
TERMINAL STRIP (CUSTOMER CONNECTION)
NB - NEUTRAL BLOCK
LIMIT SWITCHES, ACTUATOR
VARISTOR
FUSE, 5A
VR1,VR2
F1,2,3 & 4
XA1,XB1
NB
TB
TR
194
TB6
TB7
194
23 23
B
TR
A
A
B
B
A
126
1
E1
N2A
* - NOT USED WITH PREPACKAGED
STANDBY GENERATORS
TRANSFER SWITCH CONTACTOR
SOLENOID COIL (STANDBY CLOSING)
SOLENOID COIL (UTILITY CLOSING)
LEGEND
TR
ATS
C1
C2
N2A
NB
205
6 9
E2
00
T2A
T1A
E2
F4
LOAD 2
UTILITY 2
NEUTRAL *
(OPTIONAL)
F2
TB2
TB5
TB4
N2
T2
LOAD 1
F3
TB3
T1
ATS
N1A
N1A
7
E1
N2A
UTILITY 1
F1
TB1
N1
NO
XA1
COM
C1
VR1
COM
XB1
NO NC NC
C2
VR2
FROM
GENERATOR
UTILITY SOURCE
N1
E1
E2
N2
T1 T2
LOAD
— SUPPLY INPUT TO
CONTROL
BOARD
— SUPPLY INPUT TO
CONTROL
BOARD
— LOAD INPUT TO
CONTROL
BOARD
— LOAD INPUT TO
CONTROL
BOARD
= 12 VDC ALWAYS PRESENT
= AC VOLTAGE
= GROUND FOR CONTROL PURPOSES