YORK YK — PHASE A (OR B,C) OVERCURRENT FAULT

The message appears on the VSD display as PHASE A (OR B,C) OVERCURRENT FAULT. The manual prints it in this single form; the parenthetical means the same overcurrent shutdown may be shown for phase A, B or C.

This is a shutdown generated by the VSD if the motor current exceeds a given limit. The motor current is sensed by the Current Transformers on the VSD output pole assemblies, and the signals are sent to the VSD logic board for processing. Which limit applies depends on the rating of the unit; the maximum instantaneous permissible currents are listed below.

• A voltage sag on the utility power feeding the VSD. If the chiller trips, then restarts and runs without a problem, the manual attributes the trip to a voltage sag on the utility power feeding the VSD that is in excess of the specified dip voltage for this product — especially if the chiller was running at, or near, full load. With a sudden dip in line voltage the current to the motor increases, since the motor wants to draw constant horsepower, and the vanes cannot close quickly enough to correct for this sudden increase in current.
• An output pole problem. If the chiller will not restart but keeps tripping on this same shutdown, an output pole problem is the most likely culprit, and the VSD most likely requires service.

1. Restart the chiller after the trip and watch whether it runs without a problem.
2. If it restarts and runs normally, look at the utility power feeding the VSD: a sag in excess of the specified dip voltage for this product is the likely cause, above all if the chiller was running at, or near, full load when it tripped.
3. If the chiller will not restart and keeps tripping on this same shutdown, treat an output pole problem as the most likely culprit — the VSD most likely requires service.

Maximum instantaneous permissible currents, by unit rating:

• 351/292 HP = 771 Amps
• 503/419 HP = 1200 Amps
• 790/658 HP = 1890 Amps
• 1100/900 HP = 3093 Amps