An electric circuit breaker containing electromagnetic-assist means for opposing the contact-repulsion forces developed when a high current flows through the breaker. The electromagneticassist means comprises a rigid support member which when restrained in a fixed position renders the assist means capable of transmitting closing force to the movable contact but which, when released, disable the assist means. Releasable latching means restrains the support member in said fixed position when the contacts are engaged. This latching means is controlled by the motion of a contact-operating member that is coupled to the movable contact through a suitable wipe mechanism.