M

M - Abbreviation for meter. Also abbreviation for milli when used in conjunction with other units (e.g. Msec).

M - Abbreviation for mega (meaning 1,000,000 or 106), used as a prefix to units (e.g. MHz).

Magnetic field - The magnetic field of force surrounding a current-carrying conductor.

Maximum operating voltage - Maximum allowable continuous sinusoidal voltage (RMS) at 50-60 Hz. If suppressor is exposed to a continuous voltage higher than RMS voltage stated in specification, the suppressor may suffer damage.

MCB - Abbreviation for main circuit breaker

MCCB - Abbreviation for molded case circuit breaker

Measured Limiting Voltage - The maximum magnitude of voltage that is measured across the terminals of the SPD during the application of impulses of specified wave shape and amplitude.

Meshed earthing system - A system of earth electrodes or earth conducts that has been interconnected so as to form a grid or mesh or interconnections.

Metal cladding - The metal outer layer or skin used in the construction of many industrial buildings.

Metallic - See differential mode

Metal Oxide Varistor (MOV) - A type of suppression component. In standby mode, the MOV presents a very high resistance in shunt with the power line, drawing negligible current. When an incoming transient exceeds a critical voltage threshold, the MOV switches rapidly to a near "short-circuit" diverting mode, handling thousands of transient amperes. When the transient surge expires, the MOV components reset instantly to the reset mode, ready to respond to future transients.

Micro - A prefix to units of measurement meaning one millionth or 10-6. It is symbolized by the Greek letter µ (e.g. µsec).

Milli (M) - A prefix to units of measurement meaning one thousandth or 10-3 (e.g. Mm or ms).

Mode - Synonym for transmission mode. With regard to transient overvoltages the term is used to describe the pair or pairs of conductors that transient overvoltages exist between.

Modes of protection - Refers to the presence of surge suppression components connected between phases to neutral, phases to ground, neutral to ground, and between phases. (See common mode and normal mode).

Moisture barrier - Outer layer of, most typically, a data communication cable designed to protect its conductors from moisture.

Mutual inductance - See inductance