An interlock (15) for electric power switches (1a, 1b) includes indicator followers (23a, 23b) each following a state indicator (9) on an associated electric power switch (1) indicating the open/closed state of the switch. A first coupler (57 1, 57 2 ) couples (57 1, 57 2 ) one end (59) of an associated elongated connecting member (55) to each indicator follower (23). A second coupler (77a, 77b) couples the other end (79) of each elongated connecting member (55) to an auxiliary trip member actuator (39) which actuates an auxiliary trip member (13) on another electric power switch (1) to maintain it in the open/tripped condition when the associated electric power switch is in the closed condition. The first couplers (57) include a swivel (63) through which the elongated connecting member (55) slides and a compliant member (67), preferably in the form of a helical compression spring, captured between the swivel (63) and a stop nut (69) on the one end of the elongated connecting member (55).