Medium Voltage

Standards

• Arc-Flash Study

  The arc-flash study for a project's electrical power distribution system: the incident energy and the arc-flash boundary at every bus a worker examines, adjusts, services, or maintains while it is energized, on AC systems from 208 V through 38 kV with utility, generator, inverter-based, and paralleled sources, and on the DC side of battery, energy storage, and photovoltaic equipment where the project includes it. Covers who performs the study and when it is issued, the IEEE 1584-2018 method and the methods applied outside its range, the buses studied, the source operating cases and the maintenance-mode cases, the arcing current variation, the clearing time taken from the accepted coordination settings, the arc-flash input data the system model does not already carry (electrode configuration, enclosure dimensions, bus gap, working distance), the content of the arc-flash label, the PPE arc rating the facility's safety program consumes, the mitigation recommendations, the report, and the five-year review and the events that call for a re-study.

• Distribution Transformers (Superseded)

  never for new adoptions — this standard has been split and superseded. For dry-type transformers rated 600 V and below use Low Voltage Dry Type Transformers; for transformers with a primary above 600 V (liquid-immersed pad-mounted and MV dry-type) use Medium Voltage Transformers.

• Electrical Equipment Labels

  The labels, nameplates, directories and signs applied in the field to the enclosures of electrical equipment rated 1000 V and below, and of the medium-voltage equipment on the same project: switchgear, switchboards, panelboards, motor control centers, transformers, transfer switches, generators, drives, disconnects, starters, busway, meter enclosures and control enclosures. Covers the equipment identification nameplate with its designation and source, the nameplates on each device and compartment, the circuit directory, the warning and danger signs NFPA 70 requires on equipment for voltage, multiple sources, disconnect location, back-fed devices, series ratings and ungrounded systems, the arc-flash warning label as a product and its installation, the available fault current marking, service equipment signs, the marking of emergency and standby system equipment, nameplate material, colors, character heights and attachment, the ANSI Z535.4 format of safety signs, installation, warranty and spare stock.

• Medium Voltage Switchgear

  Metal-clad medium-voltage switchgear rated above 1 kV through 38 kV using drawout vacuum or SF6 circuit breakers, built to IEEE C37.20.2 and the ANSI/IEEE C37.04 / C37.06 / C37.09 series, for utility-customer substations, large commercial campuses, healthcare and higher-education central plants, data centers, and industrial facilities. Covers 5 kV, 15 kV, 27 kV, and 38 kV voltage classes, indoor and outdoor walk-in (protected aisle) configurations, arc-resistant ratings per IEEE C37.20.7, multifunction microprocessor protective relays, and optional IEC 61850 station bus communications.

• Protective Device Coordination Study

  The time-current coordination study for a project's electrical power distribution system, from the utility's protective device at the point of delivery through every overcurrent protective device within the extent the datasheet selects, on AC systems rated 1000 V and below through 38 kV with utility, generator, inverter-based, and paralleled sources. Covers who performs the study and when it is delivered, the degree of coordination applied to normal distribution and the circuits on which NFPA 70 620.62, 645.27, 700.32, 701.32, 708.54, and 517.31(G) require selective coordination, the coordination time intervals and band separations, the curves of the utility device, transformers, motors, conductors, generators, and inverter-based sources that bound every setting, the coordination of ground-fault protection including the two levels NFPA 70 517.17 requires, the recommended setting of every trip unit, relay, fuse, and overload relay, the trade-off between selectivity and incident energy, the coordination deficiencies and who accepts them, the settings record handed to the field, the report, and the events that call for a re-study.

• Short-Circuit Study

  The short-circuit study for a project's electrical power distribution system, from the utility point of delivery through every point at which an interrupting rating, a close-and-latch rating, a short-time withstand rating, a bus bracing rating, or a marked short-circuit current rating is confirmed, on AC systems rated 1000 V and below through 38 kV with utility, generator, inverter-based, and paralleled sources. Covers who performs the study and when it is delivered, the calculation method and the duty networks, the fault types and the maximum and minimum cases, the system model and the data it is built from (the utility's available fault current and X/R, transformer impedances, conductor impedances and lengths, motor and generator contribution, inverter-based sources, and the survey of existing equipment on a renovation), the source operating cases, the equipment duty evaluation, the treatment of series-rated combinations, the available fault current and date that NFPA 70 110.24 requires at the service equipment, the report and the model handed to the coordination and arc-flash studies, and the events that call for a re-study.

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