Abstract: An interlock, for a pair of electromagnetic switches, includes operating members which are pivoted by movement of armatures of the switches between off and on positions. Ring segment cams are carried by the respective operating members along arcuate paths which intersect such that movement of one switch out of the off position mechanically blocks movement of the armature of the other switch out of the off position. For side by side electromagnetic switches, the operating members are directly confronting. For other arrangements of the switches, such as one above the other, the operating member of one switch includes a first pivot member pivoted by the associated armature, and a second pivot member on which the ring segment cam is carried, confronting the second operating member, and connected to and pivoted with the first pivot member by a connecting member.