DC breaker

A DC breakers and in particular to DC breaker modules suitable for use in a high voltage DC circuit. The breaker module comprises at least a first breaker circuit (enclosed within a conductive enclosure. The enclosure is configured such that the first breaker circuit can be connected (in an electrical path with a circuit external to the conductive enclosure. The conductive enclosure is further configured to be connected to a node of the electrical path such that, in use, the conductive enclosure is at the same voltage potential as the node of the circuit path. The conductive enclosure may be a standardised size and may, for example, be a standard shipping container. The methods and apparatus of the present application allow a DC breaker to be formed from modules that can be built, tested, transported and installed in a standardised enclosure.