a switchable adaptor for receptacles includes a manually settable switch that may be manually tripped or tripped by a solenoid in response to a signal . the switch is readily converted to be normally on or normally off , and to be unipolar or multipolar . the adaptor may conveniently be in the form of a power bar or a power block , and will normally include a circuit board which may incorporate a circuit suitable for generating a signal responsive to a predetermined input condition .