NUT 2993423 - Caterpillar

All Automatic Transfer Switches Described By 9Y7900 Chart
(Area A) pickup and dropout below 85 percent. (Area B) pickup and dropout above 85 percent.New utility voltage pickup and dropout adjustments should be used on 9Y7998 Voltage Sensing Board for proper transfer switch operation. With settings below the 85 percent line (area A) a single phase voltage loss or decrease of the utility voltage may not be detected by the transfer switch. If a single phase voltage decrease or loss is not detected, the standby engine generator set will not be given a signal to start and transfer the load. Settings must be above the 85 percent line (area B) for the voltage sensing board to properly detect a decrease or loss of a single phase voltage. The voltage sensing board will detect a single phase voltage loss of a returning utility, even with the pickup adjustment set to the lowest setting (85 percent on new sensing boards. Do not adjust older sensing boards to pickup voltage below 85 percent.
Current production 9Y7998 Utility Voltage Sensing Circuit Boards have a new adjustment range. The pickup range is 85 to 95 percent and the dropout range is 75 to 95 percent.