DC CIRCUIT BREAKER AND DISCONNECTOR

A circuit breaker / disconnector apparatus for use in a power delivery system comprises a unidirectional DC circuit breaker (20) which has a first terminal (21) and a second terminal (22) and is configured to automatically open during an overcurrent condition in a forward direction and to remain closed independent of current level in a reverse direction. A disconnector switch (10) is in series with the circuit breaker. The disconnector switch (10) has a first terminal (11) for connecting to a first polarity connector (2) of a power supply (1), a second terminal (12) for connecting to a second polarity connector (3) of the power supply (1) and a common terminal (13) connected to the first terminal (13) of the circuit breaker. The disconnector switch (10) has at least a first position in which the first terminal (11) is connected to the common terminal (13) and a second position in which the second terminal (12) is connected to the common terminal (13). The second polarity connector (3) of the power supply (1) may be coupled to a track of a transport system and the second polarity connector (3) of the power supply (1) may be coupled to a live overhead cable or live third rail of a transport system. The apparatus can be used to safely ground the live cable or third rail when in a maintenance condition.