Discrimination is the allocation and selection of protective devices within a complete electrical system, ensuring that the device closest to a fault, if a fault were to occur, would open rather than any upstream device. This purpose to ensure that the fault is isolated and only the fault, therefore obviously depending on where the fault is but supply to the rest of the building and all its ancillaries are maintained without disruption.

For example, let's say a fault in a motor circuit in a manufacturing organisation were to occur, this should result in the protective device for that circuit and that circuit only opening while all other building supplies remain energised. If this fault resulted in the opening of the buildings main incoming breaker this would isolate the complete building over what could be a single item within a