AI-1
APPENDIX I
GLOSSARY
ACTUATOR—The part of a switch that is acted upon to cause the switch to change contact connections;
e.g., toggle, pushbutton, and rocker.
AMMETER—A meter used to measure current.
ARC EXTINGUISHER—The part of a circuit breaker that confines and divides the arc that occurs
when the contacts of the circuit breaker open.
ARMATURE—In a relay, the movable portion of the relay.
BREAK—In a switch, the number of breaks refers to the number of points at which the switch opens the
circuit; e.g., single break and double break.
BURNISHING TOOL—A tool used to clean and polish contacts on a relay.
CONTINUITY—An uninterrupted, complete path for current.
DAMPING—The process of smoothing out oscillations. In a meter, damping is used to keep the pointer
of the meter from overshooting the correct reading.
D’ARSONVAL METER MOVEMENT—A name used for the permanent-magnet moving-coil
movement used in most meters.
DIRECT SHORT—A connection between two points in a circuit, such as between a component and
ground.
ELECTRODYNAMIC METER MOVEMENT—A meter movement using fixed field coils and a
moving coil; usually used in wattmeters.
ELECTROMAGNETISM—The relationship between magnetism and electricity.
ELECTROSTATIC METER MOVEMENT—A meter movement that uses the electrostatic repulsion
of two sets of charged plates (one fixed and the other movable). This meter movement reacts to
voltage rather than to current and is used to measure high voltage.
FERRULES—The cylindrical metallic ends of a cartridge fuse.
FREQUENCY METER—A meter used to measure the frequency of an ac signal.
GALVANOMETER—A meter used to measure small values of current by electromagnetic or
electrodynamic means.
HOT WIRE METER MOVEMENT—A meter movement that uses the expansion of a heated wire to
move the pointer of a meter; measures dc or ac.
IN-CIRCUIT METER—A meter permanently installed in a circuit; used to monitor circuit operation.
