AI-3
RELUCTANCE—The resistance of a magnetic path to the flow of magnetic lines of force through it.
ROTARY SWITCH—A multicontact switch with contacts arranged in a circular or semi-circular
manner.
SENSITIVITY—(1) For an ammeter: the amount of current that will cause full-scale deflection of the
meter. (2) For a voltmeter: the ratio of the voltmeter resistance divided by the full-scale reading of
the meter, expressed in ohms-per-volt.
SHORT CIRCUIT—An unintentional current path between two components in a circuit or between a
component and ground which is usually caused by a malfunction in the circuit.
SHUNT RESISTOR—A resistor in parallel. In an ammeter, shunt resistors are used to provide range
capability.
SNAP-ACTING—Changing position quickly with the aid of a spring.
SOLENOID—An electromagnetic device that changes electrical energy into mechanical motion; based
upon the attraction of a movable iron plunger to the core of an electromagnet.
SWITCH—A device used to open or close a circuit.
TEST EQUIPMENT—A general term applied to devices used to test electrical and electronic circuits.
THERMAL TRIP ELEMENT—A circuit breaker trip element that uses the increased bending of a
bimetallic strip caused by increased current to open a circuit.
THERMAL-MAGNETIC TRIP ELEMENT—A single circuit breaker trip element that combines the
action of a thermal and a magnetic trip element.
THERMOCOUPLE METER MOVEMENT—A meter movement that uses the current induced in a
thermocouple by the heating of a resistive element to measure the current in a circuit; used to
measure ac or dc.
THROW—In a switch, the number of different circuits each pole can control; e.g., single throw and
double throw.
TRIP-ELEMENT—The part of a circuit breaker that senses any overload condition and causes the
circuit breaker to open the circuit.
TRIP-FREE CIRCUIT BREAKER—A circuit breaker that will open a circuit even if the operating 5
mechanism is held in the ON position.
TROUBLESHOOTING—The process of locating and repairing faults in electrical or electronic
equipment.
VOLTMETER—A meter used to measure voltage.
WAFER SWITCH—A rotary switch in which the contacts are arranged on levels. Each level is
electrically independent but mechanically connected by the shaft of the switch.
WATT-HOUR METER—A meter used to measure electrical energy.
WATTMETER—A meter used to measure electrical power.
