Incident Energy Reduction Methods

Ground Fault Circuit Interrupter

A ground fault circuit interrupter compares the current moving into and out of a piece of electrical equipment to detect hazardous differences. If the deviation exceeds a determined value, the device rapidly breaks the circuit, preventing a potential short circuit.

Ground fault circuit interrupters can be incorporated as permanent design features that work with fuses, breakers, and other safety mechanisms to reduce the possibility and duration of arc flash events. Temporary interrupters may also be applied to improve the safety of a worksite.

Zone-Selective Interlocking

This method allows two or more circuit breakers to communicate with each other so that a short circuit or ground fault is cleared by the breaker nearest to the fault. Clearing the fault in the shortest time helps reduce the incident energy created.

Differential Relaying

This method works by ensuring the current flowing into the equipment is equal to the current output. If the two currents are not equal, a fault must exist within the equipment, and the relaying can be set to operate for a fast interruption. Differential relaying uses current transformers located on the line and load sides of the equipment and fast-acting relay.

Energy-Reducing Maintenance Switching with Local Status Indicator

This switch allows a worker to set a circuit breaker trip unit to operate faster while the worker is working within an arc flash boundary. After the work is complete, the worker sets the breaker back to a normal setting.

Energy-Reducing Active Arc Flash Mitigation System

This system reduces the arcing duration by creating a low-impedance current path within a controlled compartment. This causes the arcing fault to transfer to the new current path while the upstream breaker clears the circuit. The system works without compromising existing selective coordination in the electrical distribution system.

Arc Flash Relay

This method typically uses light sensors to detect the light produced by an arc flash. When a certain light level is detected, the relay will issue a trip signal to an upstream overcurrent device.

High-Resistance Grounding

The majority of electrical faults are of the phase-to-ground type. High-resistance grounding inserts impedance in the ground return path and typically limits the fault current to 10 amperes and below (at 5 kV nominal or below). This leaves insufficient fault energy and helps to reduce the arc flash hazard level. This method will not affect arc flash energy for line-to-line or line-to-line-to-line arcs.

Current-Limiting Devices

These protective devices reduce incident energy by clearing the fault faster and by reducing the visible current at the arc source. The energy reduction is effective for current above the current-limiting threshold of the current-limiting fuse or current-limiting circuit breaker.

To learn more about Arc Flash Safety visit our OSHA Construction Arc Flash Safety Online Training web page.