Electrical Contractor Terminology Glossary M

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Glossary MElectrical Contractor Terminology used by Goodiel Electric, LLC.

MAC address – Media Access Control address is a unique numeric identifier assigned to each device connected to an Ethernet network. It is used for data transmission and security functions.
Main Protection – The protection system which is normally expected to operate in response to a fault in the protected zone.
Major Roadway (Lighting) – That part of the roadway system that serves the principal network for through-traffic flow. The routes connect areas of principal traffic generation and important rural highways entering the city.
Maximum Permissible Values of the input current and voltage – Values of current and voltage assigned by the manufacturer which the transducer will withstand indefinitely without damage.
Mbps – Megabits per second. A megabit is roughly a million bits of data . This abbreviation is used to describe data transmission speeds, such as the rate at which information travels over the internet.
MCC – Motor Control Center.
MCCB – Molded Case Circuit Breaker.
Mean-Sensing Transducer – A transducer which measures the mean or average value of the input waveform but which is adjusted to give an output corresponding to the r.m.s. value of the input when that input is sinusoidal.
Measured – A quantity subjected to measurement.
Measuring Element – A unit or module of a transducer which converts the measurand, or part of the measurand into a corresponding signal.
Measuring Range – The part of the span where the performance complies with the accuracy requirements.
Measuring Relay – An electrical relay intended to switch when its characteristics quantity, under specified conditions and with a specified accuracy attains its operating value.
Medium Distribution (Lighting) – A luminary is classified as having a medium light distribution when its max candlepower point falls between 2.25MH – 3.75MH TRL. The maximum luminaire spacing-to-mounting height ratio is generally 7.5 or less.
Medium Voltage – An electrical system or cable designed to operate between 1kv and 38kv.
Megohmmeter – A testing device that applies a DC voltage and measures the resistance (in millions of ohms) offered by conductor’s or equipment insulation.
Melt Time – The time needed for a fuse element to melt, thereby initiating operation of the fuse. Also known as Fuse Melt Time.
Mercury Vapor Lamp (MV) – An HID light source in which the arc tube’s primary internal element is Mercury Vapor.
Messenger – A bare wire used to support power or communications cables suspended overhead.
Metal Clad (Switchgear) – An expression used by some manufactures to describe a category of medium voltage switchgear equipment where the circuit breakers are all enclosed in grounded, sheet-steel enclosures. Such enclosures may be suitable for indoor use or may be enclosed.
Metal Enclosed (Switchgear) – An expression used by some manufacturers to describe a category of low voltage, 600 volt class switchgear equipment, where the circuit breakers are all enclosed in grounded, sheet-steel enclosures. Such enclosures normally are suitable only for indoor use.
Metal Halide Lamp (MH) – An HID light source in which the arc tube’s primary internal element is Mercury Vapor in combination with Halides (salts or iodides) of other metals such as Sodium or Scandium.
Metering (non-tariff) – Values computed depending on the values of digital or analog inputs during variable periods.
Metering (tariff) – Energy values computed from digital and/or analog inputs during variable periods and dedicated to energy measurement for billing purposes.
MHR (Lighting) – Mounting Height Ratio.
Micro- – One-millionth.
Mid Point Sectioning Substation – A substation located at the electrical interface of two sections of electrified railway. It contains provision for the coupling of the sections electrically in the event of loss of supply to one section.
Mil – One-thousandth of an inch (0.001 inch).
Mobile Transformer – A transformer that often is mounted on a leak proof base and can be installed and operated in a semi-trailer, box truck or sea freight container.
ModBus – Proprietary communication protocol used on secondary networks between HMI, substation computers or Bay computers and protective relays.
Modem – Device utilized to convert computer data into sound that can be transmitted over phone lines. First used to send telegrams the modem received the name from the process of modulation and demodulation at the receiving end.
Module (Photovoltaic) – See “Photovoltaic Module”.
Momentary Rating – The rating of a device to withstand momentary, very high current, without incurring damage.
Mortality Curve – A graphic representation of lamp burnout as a function of time.
Motion Resistant Conductor – ACSR with Motion Resistant Variable Profile.
MOV – Metal Oxide Varistor.
MRO – Maintenance and Repair.
MTW – Machine tool wire, used for electrical connections inside equipment.
Multi-Crystalline (Photovoltaic) – A material that is solidified at such a rate that many small crystals (crystallites) form. The atoms within a single crystallite are symmetrically arranged, whereas the crystallites are jumbled together.
Multi-element transducer – A transducer having two or more measuring elements. The signals from the individual elements are combined to produce an output signal corresponding to the measurand.
Multi-section transducer – A transducer having two or more independent measuring circuits for one or more functions.
Multi-shot reclosing – A re-closing scheme that permits more than one re-closing operation of a CB after a fault occurs before lock-out occurs.
MV – See “Medium Voltage”.
MVA  – Apparent Power expressed in Million Volt-Amps.
MW – Mega Watt, one million watts.
MWH – Mega Watt Hour, the use of one million watts for one hour.

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Glenn Goodiel.
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