Find the Right Switchboard Fast: Understanding UL 891, EUSERC & Annex G Standards

Oct 11,2025

UL 891 — The Foundation of Switchboard Safety

UL 891 is the primary certification standard for dead-front switchboards in the U.S. It defines construction, performance, and testing requirements to ensure the equipment can safely handle rated currents and fault conditions.
Key aspects include:

Busbar and conductor ratings

Short-circuit withstand and temperature rise tests

Enclosure and grounding requirements

Accessibility and operator safety

Manufacturers with UL 891 certification can demonstrate that their switchboards meet the safety expectations of NEC (National Electrical Code) and local authorities.

🔹 EUSERC — Utility-Driven Requirements

EUSERC (Electric Utility Service Equipment Requirements Committee) sets additional design and installation guidelines, mainly adopted by Western U.S. utilities such as PG&E, SCE, and SDG&E.
EUSERC compliance ensures that switchboards meet utility company interface and metering requirements. Typical EUSERC features include:

Dedicated metering compartments

Utility-sealable sections

Standardized conduit entry and termination layouts

For manufacturers or exporters, offering an EUSERC-compliant design can greatly simplify approval for utility-connected projects in the U.S. West Coast.

🔹 Annex G — Enhancing Design Flexibility

Annex G is an optional extension to UL 891 that allows for modular switchboard construction, similar to switchgear-style assemblies.
It provides flexibility for projects that require:

Draw-out breakers

Front/rear accessibility

More complex distribution configurations

Annex G is particularly relevant for industrial and data center applications where scalability and serviceability are key.

🔹 Why These Certifications Matter

For OEMs, panel builders, and exporters, understanding and applying these standards helps:

Ensure regulatory compliance and smooth project approvals

Improve market acceptance in North America

Strengthen brand credibility and customer trust

In summary, UL 891 sets the foundation for switchboard safety, EUSERC defines utility-specific needs, and Annex G offers design flexibility for advanced applications. Together, they form the backbone of compliant and reliable power distribution solutions in the U.S. market.