hammer break

hammer break (plural hammer breaks)

1. (electrical) An interrupter in which contact is broken by the movement of an automatically vibrating hammer between a contact piece and an electromagnet, or of a rapidly moving piece mechanically driven.
   • 1903, The Horseless Age, volume 11, page 645:

     […] a form of contact device was adopted of the commutator and brush type, having rubbing contacts only, and doing away with all platinum points and hammer breaks.