1 Scope

1.1 This Standard applies to service-entrance, feeder, and branch-circuit busways and associated fittings rated at 1000 V or less, 6000 A or less, and intended for use in accordance with the Canadian Electrical Code, Part I (CE Code, Part I), NFPA 70^®, National Electrical Code^® (NEC^®), and the Mexican Standard for Electrical Installations (Utility), NOM-001-SEDE. These requirements do not apply to metal enclosed bus intended for connecting switchgear assemblies for use in prefabricated electric distribution systems.

NFPA 70^®, National Electrical Code^®, and NEC^® are registered trademarks of the National Fire Protection Association, Quincy, MA.

1.2 For the purpose of these requirements, a busway is considered to be a grounded metal enclosure containing factory-mounted conductors that are usually copper or aluminum bars, rods, or tubes.

1.3 Requirements stated throughout this Standard for fittings apply to tap boxes, feed boxes, plug-in devices, and similar fittings, but do not apply to busway elbows, tees, and crosses.

Summary of Topics

This new Fourteenth Edition of ANSI/UL 857 dated September 10, 2025 includes Clarification of the Scope, Clarification of Requirements for Continuous Plug-In Busways, Revision of Minimum Clearance and Creepage Distances for 601 – 1000 V, Define Stabilization for Section 16 Temperature Rise Limits (Stabilization Method), Clarification for Short Circuit Sample Selection, Revise Markings to Reflect Limitation of One Service Disconnect in a Busway Fitting, Removal of Reference to Standard UL 512 from Annex A, and Editorial Changes throughout this Standard.