The 2C81 is a DC current measuring relay. The measured input current is derived from a mV drop across a current shunt. A switchmode power supply provides a very wide auxiliary operating range. A relay fail alarm is provided in the form of a C/O contact which is picked up when the auxiliary supply is healthy.
The 2C81 relay may be applied to provide a trip signal to a circuit breaker in a DC system in the event of a short circuit on the downstream side of the CB. An integrated timer may be specified to provide an adjustable delay to allow coordination with other protective devices.