Standard for Switchboards

1.1 Scope and object

1.1.1 This Standard applies to switchboards nominally rated at 1 000 V or less and intended for use in accordance with the Canadian Electrical Code, Part I (CE Code, Part I), the National Electrical Code (NEC), ANSI/NFPA 70, and the Mexican Standard for Electrical Installations (Utility), NOM-001-SEDE.

1.1.2 In this standard the term switchboard is intended to refer to a dead-front switchboard.

1.1.3 These requirements do not cover the following switchboard types: preset and dimmer control (theater), live front, railway control or electrification; or constructions intended only for receiving motor control center units.

1.1.4 These requirements cover switchboards for use on circuits having available short-circuit currents of not more than 200 000 A.

1.1.5 These requirements do not cover switchboards with short-time current ratings.

Summary of Topics

This revision of ANSI/UL 891 dated March 21, 2025 includes the following revised or added requirements:

– Revision of Requirements for Multiple Source Switchboards; 3.27, 6.2.1.1, 6.3.4.4.1 – 6.3.4.4.7, 8.1.15.1, 8.6.5.2, 8.6.5.6 – 8.6.5.9, Annex B, and Annex C. – Addition of Requirements for Forced-Air Cooling for Switchboards; 3.30A, 6.2.1.2, 8.2.1.3.9 – 8.2.1.3.12, and 9.2.2.1. – Modification of Requirements for Emergency Circuits; 6.2.4.1 – 6.2.4.3, 8.6.11.13, and Annex C. – Update Requirements in UL 891 to Reflect Changes to the 2020 Edition of the NEC; 6.2.7.22, 6.2.7.22.1, 8.8.2.3.15, and Annex C. – Revisions to Requirements for Service Equipment Use; 8.1.11.1 – 8.1.11.6.6, Figure 19, Figure 20, 8.7.1.5, and 8.7.1.6. – Addition of Requirements for Dielectric Testing with a Range of Source Frequencies; 8.1.17.3, 9.2.3.1, 9.2.3.4.1, 9.2.3.5.1, and 9.3.1.1.1. – Voltage Ratings for High-Impedance Neutral Grounded Systems; 8.4.8.1 – Revision of Requirements for Minimum Conductor Size for High Impedance Grounded Neutral Systems; 8.4.8.6 and Annex B. – Addition of Requirements for Panelboards Mounted in a Face-Up Position; 8.6.9.3 – Addition of Requirements for Connection of Devices Within Annex G; 9.1.1.2.2, 9.1.1.2.7, 9.2.4.1.5.1.1, 9.2.4.1.5.1.1A, G3.4 and G3.5. – Revision of Temperature Stabilization Requirements in 9.2.2.15 – Revision of Annex D – Revision of "Nominal" Bus Bar Size to a "Minimum" Bus Bar Size in Annex G; G3.1.3, Table G3.1, and G3.1.4. – Clarification of Requirement in Annex G for Distance from Connector to Closest Support; G3.2.1. – Reduction of the Threshold Limit of Single Pole Inlets Requiring Interlocking; 8.8.4.2.5. – Deletion of Reference to Standard UL 1054 from Annex A – Editorial corrections; 9.2.4.2.4.1.4 and SA1.2.