Do UL 891 Switchboards Really Require Fully Insulated Busbars? Let's Clear It Up

In North America, UL 891 is one of the key safety standards for low-voltage switchboards. A common belief in the market is that UL891 requires busbars to be fully epoxy coated, with all joints completely covered and no exposed conductors. This is not accurate.
UL891 is a safety-focused standard. It does not mandate a specific insulation method. Instead, it focuses on overall system safety. Key requirements include dead-front protection, proper electrical clearances, short-circuit strength, and acceptable temperature rise. In simple terms, the system must prevent user contact with live parts and operate safely under rated conditions.

Under this framework, full insulation of busbars is not mandatory. It is a design option. In many UL891-compliant projects, bare copper busbars are still widely used. These are installed inside enclosed structures with barriers and proper spacing to meet dead-front and clearance requirements. This approach is fully compliant.

In higher-spec applications, partial or full insulation may be applied. For example, heat shrink tubing can be added between phases, or insulation can be used near accessible areas to increase safety margins. In more demanding environments—such as coastal sites, high humidity areas, or data centers—fully insulated busbars with epoxy coating are sometimes used. These improve corrosion resistance and long-term reliability, but they are not required by UL891.

The same applies to joints. UL891 does not require all connection points to be fully covered. Bolted joints can remain visible, as long as they are not accessible during operation and all safety requirements are met. In practice, many switchboards have exposed joints inside the enclosure. Some projects may add insulating boots, but this is usually based on customer preference, not code requirements.

The idea that “fully insulated busbars are required for UL891” is often a marketing message. It helps position a product as safer or more premium. In reality, it is an upgrade option, not a baseline requirement.

As a manufacturer focused on the North American market, DSJ Electrical specializes in UL 891 switchboards. We provide flexible busbar designs, from bare copper to fully insulated solutions, based on project needs. This ensures compliance while balancing performance and cost.

In short: UL891 does not require fully insulated or fully covered busbars. It requires a safe, dead-front system. The level of insulation depends on the application, not the standard itself.