What is UL 891 Rating?

UL 891 is a critical safety standard for dead-front switchboards. It ensures that switchboards are safe for use in electrical systems, providing adequate protection against electrical faults, overloads, and short circuits. UL 891 is the most common and widely used standard for dead-front switchboards up to 1000V, allowing the use of either UL 489 or UL 1066 circuit breakers.

Certified switchboards are constructed following specific guidelines that govern their design, materials, and overall performance. The primary goal of this certification is to protect users and equipment by ensuring the switchboard can handle electrical currents safely and reliably, minimizing the risks of electrical hazards in various applications.

What is the Difference Between UL 891 and UL 1558?

While UL 891 is a standard for low-voltage switchboards, UL 1558 applies to low-voltage metal-enclosed switchgear. Both standards focus on safety, but they cater to different applications:

• UL 891: Designed for lower-voltage systems up to 1000V, typically used in commercial buildings or light industrial setups where switchboards manage power distribution.
• UL 1558, on the other hand, is meant for more demanding environments, such as large industrial facilities. It provides more stringent requirements, including enhanced arc flash protection and higher short-circuit withstand ratings. However, UL 1558 largely mirrors the ANSI C37.20.1 standard and mandates the use of UL 1066 circuit breakers, which are short-circuit rated down to a 15% power factor. Due to this overlap with other standards, UL 1558 offers limited advantages for many common low-voltage switchgear needs, particularly for typical commercial applications where UL 891 suffices.

How Do You Qualify for UL 891 Certification?

Manufacturers must go through a thorough process to qualify for UL 891 certification. This involves:

• Meeting the design and performance requirements set by UL for switchboards.
• Ensuring products are tested and compliant with UL standards.
• Undergoing regular inspections and maintaining documentation to ensure ongoing compliance.

This certification ensures that manufacturers consistently produce high-quality switchboards that meet the rigorous requirements, contributing to safer electrical environments for end-users and installers.

What is the Maximum Voltage Permitted for a Switchboard?

The maximum allowable voltage for a switchboard section or interior is 1000V. This makes switchboards ideal for low-voltage applications, such as those commonly found in commercial and light industrial environments. These settings benefit from certified equipment that helps ensure safety, reliability, and compliance with safety regulations.

Why UL 1558 Offers Limited Advantages for Low-Voltage Switchgear

UL 1558 primarily serves highly demanding, complex electrical systems, but for many low-voltage applications, its advantages over UL 891 are minimal. Since UL 1558 mirrors many of the requirements from ANSI C37.20.1 and mandates the use of UL 1066 circuit breakers, which are short-circuit rated down to 15% power factor, its added benefits are limited for common low-voltage switchgear needs. For many commercial environments, UL 891 certified switchboards meet all necessary safety and performance standards without the additional requirements UL 1558 imposes.

What are Two Types of UL Certifications?

There are two main types of UL certifications:

• UL Listed: Indicates that a complete product, like a switchboard, has been tested and meets full safety standards.
• UL Recognized: Applies to individual components within a system, which meet certain safety standards but must be part of a UL Listed system to ensure compliance. This certification applies to parts rather than whole products, ensuring safety within larger, more complex electrical systems.