APPENDIX I GLOSSARY

AI-2 LOADING EFFECT—The effect of a voltmeter upon the circuit being measured which results in an inaccurate measurement. Loading effect is minimized by using a voltmeter with an internal resistance many times higher than the resistance of the circuit being measured. MAGNETIC TRIP ELEMENT—A circuit breaker trip element that uses the increasing magnetic attraction of a coil with increased current to open the circuit. MEGGER—Common name for a megohmmeter. MEGOHMMETER—A meter that measures very large values of resistance; usually used to check for insulation breakdown in wires. METER—A device used to measure an electrical quantity; e.g., current, voltage, and frequency. METER MOVEMENT—The part of a meter that moves. MOVING-IRON METER MOVEMENT—Same as moving-vane meter movement. MOVING-VANE METER MOVEMENT—A meter movement that uses the magnetic repulsion of the like poles created in iron vanes by current through a coil of wire; most commonly used movement for ac meters. MULTIMETER—A single meter combining the functions of an ammeter, a voltmeter, and an ohmmeter. NONTRIP-FREE CIRCUIT BREAKER—A circuit breaker that can be held ON during an overcurrent condition. OHMMETER—A meter used to measure resistance. OUT-OF-CIRCUIT METER—A meter which is not permanently installed in a circuit. Usually portable and self-contained, these meters are used to check the operation of a circuit or to isolate troubles within a circuit. PARALLAX ERROR—The error in meter readings that results when you look at a meter from some position other than directly in line with the pointer and meter face. A mirror mounted on the meter face aids in eliminating parallax error. POINT BENDER—A tool used to adjust the contact spacing on a relay. POLE—(1) One end of a magnet. (2) The number of points at which current can enter a switch; e.g., single pole, double pole, and three pole. POLE PIECE—A piece of ferromagnetic material used to control the distribution of magnetic lines of force; i.e., concentrate the lines of force in a particular place or evenly distribute the lines of force over a wide area. RANGES—The several upper limits a meter will measure as selectable by a switch or by jacks; e.g., a voltmeter may have ranges of 1 volt, 2.5 volts, 10 volts, 25 volts, and 100 volts. RECTIFIER—A device used to convert ac to pulsating dc. RELAY—An electromagnetic device with one or more sets of contacts which changes position by the magnetic attraction of a coil to an armature.