What is the minimum trip current of an OCR in relation to the normal load current rating?

The minimum trip current of an Overcurrent Relay (OCR) is often set to be at least twice the normal load current rating. This setting ensures that the relay can effectively distinguish between normal operating conditions and fault conditions, such as short circuits or overloads.

When the load current is at its normal rating, the OCR should not trip, as this would compromise the reliability of the system. By setting the trip current to twice the normal load, the OCR is calibrated to withstand temporary surges that can happen during normal operations, while also being sensitive enough to protect the system from damaging fault currents that are significantly higher than the normal operating current.

In summary, having the minimum trip current set at twice the normal load provides a balance between safety and functionality, allowing for operational flexibility while also ensuring protection against overcurrent situations.