Overcurrent protection

Overcurrent protection detects current above a specified threshold or time-current characteristic and disconnects or limits the circuit to reduce damage and fire risk.

Overcurrent relay: A relay that detects excessive current and initiates circuit interruption according to its operating settings. It implements threshold and time-current decisions in many power-system protection schemes.
Overcurrent: Electrical current greater than the normal or rated current for a circuit or device. It is the condition this protection is designed to detect.
Motor protection: Methods and devices that protect electric motors from damaging electrical and thermal conditions. Motor circuits need overcurrent settings that accommodate starting current yet detect faults.
Earth-fault protection: Protection that detects current flowing from a circuit conductor to earth or grounded equipment. Sensitive earth-fault protection can detect leakage too small to trigger ordinary overcurrent settings.
Inverse-time overcurrent protection: Overcurrent protection whose operating time decreases as current rises above pickup. Its delay allows brief or moderate overloads while responding faster to severe faults.
Short circuit: An unintended low-impedance connection that drives abnormally large current through an electrical circuit. Short circuits create high currents that overcurrent protection must interrupt.
Feeder protection: Protection of a distribution circuit that carries power from a substation bus to downstream loads. Feeder relays use overcurrent elements to detect and isolate downstream faults.
Differential protection: Protection that detects faults by comparing current entering and leaving a defined equipment zone. It targets internal faults by current imbalance rather than relying only on current magnitude.
Instantaneous overcurrent protection: Overcurrent protection that operates without an intentional time delay when current exceeds a high setting. It clears high-current faults rapidly, close to the protected equipment.
Electrical overload: A condition in which equipment carries more current than its rating permits for a given duration. Overload protection must distinguish sustained excess load from brief current surges.

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