UL 891 2019-07 PDF

Full title and description

UL 891 — Switchboards (Dead‑Front Switchboards). Standard covering design, construction, marking and testing requirements for dead‑front low‑voltage switchboards intended for use with the National Electrical Code (NEC), the Canadian Electrical Code, Part I, and Mexican electrical installation requirements. This edition is the 12th (published in 2019).

Abstract

UL 891 establishes safety, performance and construction requirements for dead‑front switchboards rated 1 000 V or less. It defines permitted and excluded switchboard types, limits on available short‑circuit current for covered constructions, required tests (temperature rise, dielectric, short‑circuit and mechanical), marking and installation instructions intended to reduce shock and fire hazards in distribution equipment.

General information

• Status: Current (12th edition, in-force reference edition published 2019).
• Publication date: July 19, 2019 (12th edition).
• Publisher: Underwriters Laboratories (UL); the standard is published in a trinational form with CSA Group and ANCE (Mexico) for harmonized use.
• ICS / categories: 13.260 — Protection against electric shock / live working (electrical equipment safety).
• Edition / version: 12th edition (2019).
• Number of pages: Approximately 180–194 pages (page counts reported by distribution outlets vary by file format/packaging).

Scope

This standard applies to dead‑front switchboards nominally rated 1 000 V or less and intended for use in accordance with the National Electrical Code (NEC/ANSI‑NFPA 70), the Canadian Electrical Code, Part I, and Mexican installation rules (NOM). It covers switchboards intended for systems with available short‑circuit currents up to 200 000 A and excludes certain specialized constructions such as preset/dimmer theater control, live‑front switchboards, railway control/electrification assemblies, and enclosures intended only to receive motor control center units. Short‑time‑rated switchboards are not covered.

Key topics and requirements

• Definitions and classification of "switchboard" as a dead‑front assembly and excluded types.
• Voltage and current ratings (nominally ≤ 1 000 V) and maximum available short‑circuit levels (coverage up to 200 000 A).
• Constructional requirements: enclosures, bus configurations, clearances, insulation, and accessibility of live parts.
• Temperature‑rise limits and testing procedures to verify thermal performance under rated loads.
• Short‑circuit (fault) testing and requirements for withstand and protective device coordination where applicable.
• Dielectric and impulse testing for insulation integrity and separation criteria.
• Marking, nameplate data, instructions for installation, and required documentation for field personnel.
• Requirements for grounding, bonding, and protection against electric shock and fire.

Typical use and users

UL 891 is used by electrical equipment manufacturers (switchboard builders), certification bodies, electrical engineers, design consultants, electrical inspectors and facility owners to design, build, test and certify low‑voltage dead‑front switchboards for commercial, industrial and institutional power distribution. It is also used by utilities and contractors to ensure switchboards meet recognized safety and performance criteria before installation.

Related standards

UL 891 is published in a harmonized (trinational) form with CSA C22.2 No. 244‑2019 and the Mexican NMX standard (NMX‑J‑118/2‑ANCE). It is intended for coordinated use with the National Electrical Code (ANSI/NFPA 70), the Canadian Electrical Code, Part I, and may be referenced alongside other equipment and switchgear standards (for example, applicable UL standards for overcurrent protective devices, enclosures and low‑voltage switchgear).

Keywords

UL 891, switchboards, dead‑front, low‑voltage switchboards, switchgear, temperature rise, short‑circuit testing, NEC, CSA C22.2 No. 244, NMX, marking, grounding, bus ampacity.

FAQ

Q: What is this standard?

A: UL 891 is the Underwriters Laboratories Standard for Switchboards (dead‑front). It sets safety, construction and performance requirements for low‑voltage switchboards intended for normal commercial and industrial distribution systems.

Q: What does it cover?

A: It covers dead‑front switchboards rated 1 000 V or less, including requirements for construction, electrical ratings, temperature rise, short‑circuit performance, dielectric strength, markings and installation instructions. The standard excludes live‑front designs, certain theater dimmer/preset types, railway electrification equipment and cabinets intended only to receive motor control center units. It also limits covered switchboards to systems with available short‑circuit currents not exceeding about 200 000 A.

Q: Who typically uses it?

A: Manufacturers of switchboards, testing and certification organizations, electrical designers and engineers, electrical inspectors, contractors and facility owners who need to ensure switchboards meet recognized North American safety and performance requirements.

Q: Is it current or superseded?

A: The documented 12th edition was published July 19, 2019 and is the widely referenced edition; users should check UL, CSA or national standards catalogues for any amendments or later editions published after 2019. Standards distributors and UL/CSA notices should be consulted to confirm whether any revisions or corrigenda have been issued since 2019.

Q: Is it part of a series?

A: Yes — UL 891 is part of UL’s suite of standards for electrical distribution equipment and is published in a trinational harmonized form with CSA C22.2 No. 244 and the Mexican NMX counterpart; it also interrelates with other UL/CSA standards for protective devices, enclosures and switchgear.

Q: What are the key keywords?

A: Switchboards, dead‑front, low‑voltage, temperature rise, short‑circuit, marking, NEC, CSA, NMX, UL 891.