This leaflet sets out the rules for coordinating the operation of circuit breakers in substations and on board tractive units in order to ensure interoperability of motive power stock on networks equipped with different electrification systems. Coordination is required because: the cut-out power of train-borne circuit breakers is limited whereas the level of short circuit currents may exceed it under some power supply voltages; if there is no OHL voltage, the tractive unit circuit breakers must open within a maximum pre-defined time; the conditions for automatic re-closing of sub-station circuit breakers must be compatible with the preceding conditions. The leaflet specifies the limit condition of the input filter load current on tractive units under direct current power supply so that sub-station circuit breakers will not trip unnecessarily.