For an OCR to operate normally, what value of current is required to open the circuit?

The correct value of current required to operate an Overcurrent Relay (OCR) and subsequently open the circuit is typically set to twice the normal load current rating. This choice is based on the design principles of providing adequate protection for electrical circuits.

When an OCR is installed, it monitors the current flowing through the circuit. The relay is designed to operate under fault conditions, such as a short circuit or an overload, where the current exceeds the normal operating level. Setting the threshold at twice the normal load current rating allows the OCR to trip the circuit in instances of significant overloads, which can prevent equipment damage and reduce the risk of fire hazards.

By requiring a current level that is twice the normal rated load to trip the relay, it provides a buffer to distinguish between normal operation fluctuations and actual fault conditions. This helps ensure that the OCR does not trip unnecessarily during brief surges in current which can occur, for example, during motor start-up or system transients.

Although other options suggest different multipliers of the normal load current rating, they do not align with standard practices for setting relays to strike a balance between protection and operational stability. The chosen multiplier of two times normal load current is a widely accepted standard in the industry for effective overcurrent protection