A device for controlling a current in an N-phase power distribution system, the device comprising: a magnetically permeable core (21, 41) forming a loop; a plurality of coils (26, 27, 45, 46, 47) wound about the core (21, 41), wherein each coil is suitable for receiving an alternating current from the power distribution system to generate a time-varying magnetic field in the core (21, 41); a magnetically permeable bridge element (22, 42) movable between a fully-closed position (24, 50), at which a magnetically permeable path is provided along the bridge element (22, 42) between a first position on the core (21, 41) and a second position on the core (21, 41), and a fully-open position (23, 43), at which a magnetically insulating gap (25, 44) is formed between the first position and the second position on the core (21, 41); wherein the plurality of coils includes a first coil and a second coil, the first position on the core (21, 41) is located between the first and second coils on a first side of the first coil, and the second position on the core (21, 41) is located between the first and second coils on a second side of the first coil opposite the first side; wherein the plurality of coils (26, 27, 45, 46, 47) are wound about the core (21, 41) such that the alternating current in the plurality of coils (26, 27, 45, 46, 47) will generate time-varying magnetic fields in directions that will provide: a substantially zero net magnetic flux in the core (21, 41) when the bridge element (22, 42) is in the fully-open position (23, 43); and a non-zero net magnetic flux in the core (21, 41) when the bridge element (22, 42) is in the fully-closed position (24, 50); characterized in that the bridge element (22, 42) is configured to be moveable between the open position and the closed position by a mechanical actuator, and the device further comprises a controller configured to move the magnetically permeable bridge element (22, 42) between the fully-open position (23, 43) and the fully-closed position (24, 50) to control an amount of net magnetic flux in the core (21, 41) and thereby an impedance to current across the coils (26, 27, 45, 46, 47), the controller being configured to control the mechanical actuator to thereby cause the device to limit a current in the power distribution system by moving the bridge element (22, 42) to the fully-closed position (24, 50) in response to detecting that a fault exists in the power distribution system. a magnetically permeable core (21, 41) forming a loop; a plurality of coils (26, 27, 45, 46, 47) wound about the core (21, 41), wherein each coil is suitable for receiving an alternating current from the power distribution system to generate a time-varying magnetic field in the core (21, 41); a magnetically permeable bridge element (22, 42) movable between a fully-closed position (24, 50), at which a magnetically permeable path is provided along the bridge element (22, 42) between a first position on the core (21, 41) and a second position on the core (21, 41), and a fully-open position (23, 43), at which a magnetically insulating gap (25, 44) is formed between the first position and the second position on the core (21, 41); wherein the plurality of coils includes a first coil and a second coil, the first position on the core (21, 41) is located between the first and second coils on a first side of the first coil, and the second position on the core (21, 41) is located between the first and second coils on a second side of the first coil opposite the first side; wherein the plurality of coils (26, 27, 45, 46, 47) are wound about the core (21, 41) such that the alternating current in the plurality of coils (26, 27, 45, 46, 47) will generate time-varying magnetic fields in directions that will provide: a substantially zero net magnetic flux in the core (21, 41) when the bridge element (22, 42) is in the fully-open position (23, 43); and a non-zero net magnetic flux in the core (21, 41) when the bridge element (22, 42) is in the fully-closed position (24, 50); a substantially zero net magnetic flux in the core (21, 41) when the bridge element (22, 42) is in the fully-open position (23, 43); and a non-zero net magnetic flux in the core (21, 41) when the bridge element (22, 42) is in the fully-closed position (24, 50); characterized in that the bridge element (22, 42) is configured to be moveable between the open position and the closed position by a mechanical actuator, and the device further comprises a controller configured to move the magnetically permeable bridge element (22, 42) between the fully-open position (23, 43) and the fully-closed position (24, 50) to control an amount of net magnetic flux in the core (21, 41) and thereby an impedance to current across the coils (26, 27, 45, 46, 47), the controller being configured to control the mechanical actuator to thereby cause the device to limit a current in the power distribution system by moving the bridge element (22, 42) to the fully-closed position (24, 50) in response to detecting that a fault exists in the power distribution system.