A mechanical interlock assembly for a disconnector and an earthing switch. The mechanical interlock assembly comprises: a main interlock disc configured to actuate a movable contact of a disconnector, and at least one earthing switch interlock disc configured to actuate respective movable contact of at least one earthing switch respectively. The main interlock disc includes at least one first groove, and each of the at least one earthing switch interlock discs includes a third groove, and it is provided with a movable interlock pin between the main interlock disc and each earthing switch interlock disc respectively. The interlock assembly can interlock the disconnector and the at least one earthing switch, and has the advantages of a simple structure, low cost and flexibility for different arrangements. A further mechanical interlock assembly is also provided to interlock another disconnector and one of the above at least one earthing switch.