The primary components of an arc flash detection system (light and current detector) are the arc monitor unit, control unit, optical detector, current detector and current transformer. The control unit receives signals from both a high-sensitivity light detector and the upstream current transformer, enabling it to determine whether to trigger the circuit breaker. Clearly, this signalling process must be both fast and reliable to minimize 
danger and damage. Fiber optics, with its inherent speed and EMI immunity, makes it a perfect medium for an arc flash detection system.
The optical detector unit includes an optical emitter and receiver, an optical sensor in the form of a bare fiber loop, and fiber optic cable. The optical sensor collects the flash light and transfers it via fiber optic cable to the fiber optic receiver, which converts the optical signal to an electrical signal that informs the control system when an arc flash is occurring. There are two types of optical sensors commonly used in such systems:
the point sensor and the loop sensor. The point sensor approach uses a light sensor and an optical receiver to detect light in a given area, while the loop sensor uses a loop of bare fiber positioned strategically throughout the equipment.