When MSD is opening, there is an insulation distance and an obvious disconnection mark between the contacts in accordance with the requirements of the station. When MSD is losing, it can carry the current under norma| circuit conditions and abnorma| conditions within the specified time, such as short circuit.

The function of the isolating switch is to disconnect the circuit with no load current, so that the equipment under inspection and the power supply have an obvious disconnection mark to ensure the safety of the maintenance personnel. The isolating switch cannot cut off the load current and short-circuit current without a specia| arc extinguishing device. Therefore, the isolating switch can only be operated when the circuit breaker is disconnected.