You've hit on a common point of confusion and a good question. You're right, terminal block bridges rarely, if ever, have individual UL listings like the terminal blocks themselves.Here's a breakdown of why and how they're handled: Bridges as Part of a System

Terminal block bridges (also often called jumpers, cross connectors, or simply "bridges") are almost always considered accessories to the terminal blocks. They are not independently UL-listed because their safety and performance are evaluated as part of the terminal block assembly. Think of it like this: the terminal block is the primary component that establishes the connection, and the bridge is a facilitator to that connection. The UL listing on the terminal block covers its ability to safely handle current and voltage when used with compatible accessories, including bridges.

UL508A and Bus Bars

Your reference to UL508A section 29.2.2 is a good starting point. While bridges aren't exactly bus bars in the traditional sense (they're not large, rigid bars distributing power), they do function similarly in distributing current across multiple terminals. The intent of UL508A is that all current-carrying components, including bridges, must meet appropriate standards for ampacity and withstand voltage. This is achieved not necessarily through individual UL listing, but through:

Manufacturer Specifications

The terminal block manufacturer (Phoenix Contact, Wago, Weidmuller, etc.) provides detailed specifications for their bridges, including:

Ampacity

The maximum current the bridge can safely carry. This is critical and must be adhered to.

Voltage Rating

The maximum voltage the bridge is rated for.

Material

Material composition and any required certifications.

Compatibility

Specifically which terminal blocks the bridge is designed to be used with. Crucially, using a bridge not designed for a particular terminal block could void the UL listing and create a safety hazard.

UL Testing and Approval of the Terminal Block Assembly

When UL tests and approves a terminal block, they test it with the accessories that the manufacturer specifies as compatible. This testing verifies that the entire assembly (terminal block + specified bridge) can safely handle the rated current and voltage.

The System Integrator's Responsibility (You!)

As the system integrator (the company building the control panel), you are responsible for:

Selecting the Correct Bridge

Choosing the exact bridge model specified by the terminal block manufacturer for the specific terminal block you are using. This is non-negotiable.

Adhering to Ampacity Ratings

Ensuring that the current flowing through the bridge does not exceed its rated ampacity. This may involve calculating the total current drawn by all circuits connected to the bridged terminals.

Proper Installation

Installing the bridge correctly according to the manufacturer's instructions. This includes ensuring proper seating and contact.

Documentation

Documenting in your control panel's design and Bill of Materials the specific bridge models used with each terminal block. This is essential for traceability and future maintenance.

Why No Individual UL Listing? Listing every tiny accessory like a bridge would be incredibly expensive and time-consuming. It's far more practical and effective to have the manufacturer test and specify the bridge as part of the terminal block assembly, and for the system integrator to follow those specifications meticulously.

In Summary


Terminal block bridges are typically not individually UL listed.2. Their suitability is determined as part of the overall terminal block assembly's UL listing, when used with the manufacturer's specified accessories (including bridges).3. You, as the system integrator, are responsible for selecting the correct bridge model from the terminal block manufacturer, adhering to its ampacity rating, and installing it correctly.4. Document your choices!What to do in your PLM System



Don't expect to find a UL listing for the bridge itself. Instead, focus on capturing the following information in your PLM system for each bridge: Manufacturer (e.g., Phoenix Contact) Part Number (e.g., 3030323) Description (e.g., FBS 2-6) Ampacity Rating Voltage Rating* Crucially: List the specific terminal block(s) that this bridge is compatible with. This is the most important field. You might even create a relationship in your PLM system between the bridge part and the terminal block part.By managing this information carefully, you'll ensure that your designs are safe, compliant, and maintainable. If you ever have any doubts, consult the terminal block manufacturer's datasheets and application notes. They provide the definitive guidance. Flag for review