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.
