M

magnetic field: An area where magnetic forces emanate from a magnet.
magnetic synthesizer: A device made of resonant circuits including nonlinear inductors and capacitors to store energy, pulsating saturation transformers to modify the voltage waveform, and filters to filter out harmonic distortion to protect sensitive loads from voltage sags, transients, overvoltage, undervoltage, and voltage surges.
main service entrance: The enclosure that contains connection panels and breakers, located at the point where the utility power lines enter a building.
maintenance bypass: A circuit that allows maintenance personnel to repair or service equipment without affecting supply of electricity to other equipment.
make-before-break: Operational sequence of a switch or relay where the new connection occurs prior to disconnection of the existing connection.
manual bypass switch (MBS): A manually operated transfer switch that allows maintenance personal to bypass the major electronics in the UPS so the UPS can be safely serviced.
mega (M): A metric prefix meaning 1,000,000, or 10 ⁶.
megahertz (MHz): One million hertz or cycles per second.
megawatt (MW): One million watts or 1000 kilowatts.
metal oxide varistor (MOV): A component of a surge suppressor that limits overvoltage conditions (electrical surges) on power and data lines. Its resistance varies according to the rate of applied voltage and current and decreases from a very high level (thousands of ohms) to a very low level (a few ohms) when the applied voltage exceeds the breakdown point.
meter board: The board on which the main switch and associated equipment mount.
meter constant

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