Low Voltage

Standards

• Access Control Systems

  Electronic access control systems for managing pedestrian entry into commercial, institutional, and industrial buildings. Covers system architecture (standalone, networked, and cloud-managed), door controllers and panels, credential readers and credentials, electrified door hardware coordination, request-to-exit devices, door position switches, low-voltage power supplies with battery backup, controller and reader cabling, head-end software, user management and audit, fire alarm release interface, cybersecurity, and acceptance testing for swinging pedestrian doors.

• Automatic Transfer Switches

  Automatic transfer switches rated 1000 V and below, listed to UL 1008, that move a load between a normal source and an alternate source without operator action. Covers the switching mechanism, transition type, bypass-isolation construction, neutral treatment, the controller and its sensing, time delays, exerciser, load management and communications provisions, ratings including withstand and closing and short-time ratings, service-entrance construction, enclosures, identification, factory and field testing, installation, warranty, and spare parts, for switches serving emergency, legally required standby, optional standby, critical operations, and health care essential electrical system loads.

• Conductors and Cables

  Building wire and cable for power, lighting, branch circuit, and feeder applications rated 600V and below in commercial, institutional, and industrial buildings. Covers single conductors installed in raceways and cable tray, Type MC metal-clad cable, and Type AC armored cable; conductor materials (copper and aluminum); insulation types (THHN/THWN-2, XHHW-2, RHW-2, USE-2); ampacity selection and derating; voltage drop; color coding and conductor identification; splicing, connectors, and terminations; pulling and installation; insulation resistance testing; and field acceptance.

• 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.

• Grounding and Bonding for Electrical Systems

  The grounding and bonding of electrical systems rated 1000 V and below in commercial, institutional, industrial, and water and wastewater facilities: the grounding electrode system and each of its electrodes (concrete-encased, ground ring, rod, pipe and plate, structural metal, metal water pipe, electrolytic), the soil basis the electrode design rests on, the grounding electrode conductor and its routing, the service grounding including the main bonding jumper, the bonding of service raceways and the intersystem bonding termination, the grounding and bonding of every separately derived system, the equipment grounding conductors of feeders and branch circuits and the rules that size them, isolated-ground circuits, the bonding of metallic piping, structural metal and other metal systems, the common bond to the lightning protection, telecommunications and cathodically protected systems, the grounding of direct-current control systems, ground bars, exothermic, compression and mechanical connections, and the field tests that prove the installed system. Every equipment standard in the corpus hands the equipment grounding and bonding of its equipment to this standard.

• HVAC Variable Frequency Drives

  Separately procured pulse width modulated variable frequency drives rated 600 V and below, controlling three-phase AC induction motors on HVAC air and hydronic equipment — supply, return, and exhaust fans, chilled water, condenser water, and hot water pumps, and cooling tower fans. Covers drive ratings, enclosure and cooling selection, harmonic performance, bypass and disconnecting means, motor and cable compatibility, protective functions, building automation integration, testing, and installation for drives in mechanical rooms, electrical rooms, penthouses, and outdoor locations.

• Industrial Control Panels

  Factory-fabricated industrial control panels and enclosures that house instrumentation and controls (I&C) equipment for industrial, process, and water/wastewater (WTP/WWTP) facilities. Covers UL 508A listed control panels and enclosures housing programmable logic controllers, remote I/O, control relays, power supplies, network switches, and operator interface devices, rated 1000V and below. Addresses enclosure type rating selection (UL/NEMA Type 1, 3R, 4, 4X, 12), short-circuit current rating (SCCR) determination per UL 508A Supplement SB and NEC Article 409, enclosure sizing and component layout, internal power distribution and control power transformers, power-versus-signal wiring segregation, wire and terminal-block identification, thermal management, grounding and bonding, nameplates, and arc-flash labeling.

• Low Voltage Panelboards (Superseded)

  never for new adoptions — this standard has been merged into Panelboards, which carries its full content under the simple name.

• Low Voltage Switchboards

  Dead-front, floor-standing distribution switchboards rated 1000 V and below, listed to UL 891 and built to NEMA PB 2, in which molded-case or insulated-case circuit breakers, fusible switches, or bolted-pressure switches are group-mounted or individually mounted on a common bus, whether installed as service equipment or downstream of a transformer, switchgear, or another switchboard. Covers the ratings, the interrupting rating basis, the main and feeder devices and their trip units, the bus, the structure and enclosure, arc-flash mitigation, the service entrance, surge protection, metering and communications provisions built into the assembly, identification, factory and field testing, installation, warranty, and spares, for three-phase and single-phase AC systems in indoor and outdoor locations.

• Low Voltage Switchgear

  Metal-enclosed low-voltage power circuit breaker switchgear rated 1000 V and below, listed to UL 1558 and built to IEEE C37.20.1, in which drawout low-voltage power circuit breakers built to IEEE C37.13 are individually mounted in grounded metal compartments on a common bus, whether installed as service equipment, as the secondary of a transformer, or downstream of other distribution equipment. Covers the ratings and the short-time basis, the breakers and their drawout mechanisms, operation, trip units, and accessories, ground-fault protection, arc energy reduction, control power and control wiring, the protective relays, instrument transformers, metering, surge protection, and communications provisions built into the assembly, the bus, the structure and enclosure, compartmentalization and arc-resistant construction, identification, factory and field testing, installation, warranty, spares, and breaker handling equipment, for three-phase and single-phase AC systems in indoor and outdoor locations, including walk-in and non-walk-in outdoor housings.

• Motor Control Centers

  Factory-assembled, floor-standing low-voltage motor control centers rated 600 V and below, listed to UL 845 and built to NEMA ICS 18, in which combination motor starter units, reduced-voltage starter units, variable frequency drive units, feeder units, control power units, and metering units plug onto a common vertical bus fed from a common horizontal bus. Covers the assembly ratings, the enclosure and structure, the bus, the wiring class and type, arc-flash mitigation, the unit construction and the devices inside each unit, communications, identification, factory and field testing, installation, warranty, and spares, for indoor and outdoor installations.

• 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.

• Raceways and Conduit

  Conduit, tubing, and raceway systems that enclose and protect electrical power, lighting, and signaling conductors in commercial, institutional, and industrial buildings — including rigid metal conduit, intermediate metal conduit, electrical metallic tubing, flexible conduits, rigid PVC conduit, surface raceways, metal and nonmetallic wireways, and conduit fittings, boxes, and supports. Covers indoor and outdoor, exposed and concealed, wet and dry, and direct-burial raceway routing for branch circuits and feeders rated 1000V and below.

• 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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