A device with means other than fuses for automatically opening the circuit in which it is installed when the current varies from the predetermined value for which the device is set. May include provisions for manual operation. At least one set of contacts must be in series with the actuating elemen (s). A combination of semiconductor and passive devices may be used in lieu of contacts. For automatically operated items in which the actuating (tripping) element and contacts are not in series, see relay (as modified). For items which are operated both manually and automatically but the actuating elements and contact are not in series, see relay-switch. Excludes circuit breaker box and magneto "breaker" assemblies. See also switch (as modified) ; and controller.