The overcurrent relay (OCR) is an option and mounts to the subpanel that is within the control panel. The OCR provides system protection for excessive line current. The OCR is a three-phase relay. The OCR uses a solid state sensor in order to detect excessive line currents. The relay receives a signal of 0 amperes to 5 amperes from the secondary windings of the generator current transformers. Each generator is equipped with three current transformers. The transformers are sized according to the voltage rating and the kilowatt rating of the generator. The current transformer provides a 5 amp AC signal when the generator is operating at approximately 115% of the generator rating. The OCR has a setpoint for an adjustable pickup from 1 ampere to 5 amperes. The setpoint also has an adjustable time delay which allows the standard inverse time delay to be increased from 0.5 to 20 seconds. The OCR requires DC power to operate. See "DC Schematics" in Testing and Adjusting, "Schematics and Wiring Diagrams".
If one of the three-phase currents exceeds the setpoint for more than the time delay setting then contacts 11 and 12 of the OCR will close. The generator set control (GSC) will record an SP1 fault and the engine is shutdown. If the generator set is equipped with an optional circuit breaker with shunt trip, the generator is taken off the line. See the Testing and Adjusting, "Schematics and Wiring Diagrams" for more information.
After the SP1 fault is corrected, the generator set control (GSC) is reset by turning the engine control switch (ECS) to the OFF/RESET position. If the generator is equipped with shunt trip, the generator output circuit breaker must also be reset. The setpoint for the pickup can be adjusted in the field. The time delay can also be adjusted in the field. The setpoint for the pickup is set to the maximum value at the factory. The value is 115% of the generator rating.