Overcurrent

Overcurrent is an electrical condition in which the current flowing through a conductor, device, or circuit exceeds its rated capacity. It is driven by excessive load, a fault, or a combination of both, and is distinct from overvoltage. Overcurrent can be temporary or sustained and is typically addressed by protective equipment that limits damage to the electrical system.

Common forms of overcurrent include overload, short circuit, ground fault, and arcing fault. An overload occurs when a circuit carries more current than it was designed to handle for an extended period, often due to excessive load or equipment operating beyond its specification. A short circuit is a low-impedance fault that causes a very large surge of current, usually resulting from insulation failure or wiring faults. Ground faults occur when current returns to earth through an unintended path, and arcing faults involve irregular electrical arcing that can produce high fault currents.

Protection against overcurrent is provided by devices such as fuses, circuit breakers, and protective relays. Fuses interrupt current by melting a conductor element, while circuit breakers trip or switch open in response to excessive current. Protective relays, including overcurrent relays, monitor current levels and coordinate with other protective devices to isolate the faulty section. Proper coordination (selectivity) ensures only the affected portion is cleared, and devices are rated for the anticipated fault current (Ics or Isc).

Standards from organizations such as the NEC, IEC, and IEEE guide design, installation, and testing of overcurrent protection. In addition to safety and reliability implications, overcurrent can cause overheating, insulation damage, fire risk, and equipment failure if not properly prevented.