SynC · Topic
Power Distribution
These are the standards in SynC Standards that cover Power Distribution. Each one is a complete, plain-language specification: the scope it applies to, the requirements that govern it, and a structured equipment datasheet listing the values a project has to decide, with the standards each is verified against. All of it is written and maintained by SynC, free to read without an account, and published under CC BY 4.0.
A standard usually carries several topics, so most of the entries below also appear under neighbouring subjects. The topics each one carries are listed on its own page.
Standards
- 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.
- Distribution Transformers (Superseded)
never for new adoptions — this standard has been split and superseded.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.
- Low Voltage Panelboards (Superseded)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.
- 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.