You're right to be careful with UL508A compliance, it's a critical aspect of selling machines in the US. Here's the breakdown on grounding bars and UL508A

Your Assessment is Generally Correct
Grounding bars themselves typically do not need to be UL certified in the same way a component like a circuit breaker or a power supply would be. The key is the performance of the ground connection, not necessarily a specific listing mark on the bar itself. UL508A focuses on the proper execution of the grounding system as a whole, including the materials, the connections, and the testing. You're also correct about grounding braids. Grounding braids fall under the UL508A "components" part, and thus they must be certified.

Here's why your plan is likely acceptable, and the key considerations


Material and Construction



Copper is an excellent material for grounding bars. Make sure the copper is of sufficient purity and conductivity for the intended grounding application. The bar must be of adequate size (cross-sectional area) to handle the fault current it might be subjected to. This is critical. Calculations based on the expected short circuit current (SCCR) are crucial. The mechanical construction needs to be robust and durable, with sufficient thickness and support to prevent bending or breaking under normal use and fault conditions.2. Connection Integrity is Paramount



This is the most critical area. UL508A heavily emphasizes the integrity of grounding connections. Your plan to specify tightening torques is essential (see point 54.4 you mentioned). The torque specification must be appropriate for the screw/terminal size and material to ensure a reliable, low-resistance connection. Use appropriate hardware (e.g., star washers, lock washers) to maintain connection pressure and prevent loosening due to vibration or thermal cycling. Consider using a conductive anti-seize compound on the screw threads to improve connection conductivity and prevent corrosion (especially if dissimilar metals are involved).3. Documentation and Traceability

Document the specifications of the copper bar: material, dimensions, conductivity, and the source of supply. Even if not "UL listed," ensure you have material certifications or specifications from the supplier. Keep records of your torque testing and the recommended tightening torques for the grounding connections. Include this information in your control panel documentation, which will be reviewed during the UL inspection.4.

Labeling

Ensure the grounding bar is clearly labeled as the "Equipment Grounding Conductor Terminal" or similar. Properly mark all field wiring terminals with the tightening torque as required by UL508A.5.

UL Inspector Discretion

Ultimately, the UL inspector has the final say on whether the grounding system meets the requirements.* Having a well-documented, properly implemented grounding system using sound engineering principles will greatly increase your chances of passing the inspection.

In Summary

You can likely use a non-UL-listed copper grounding bar, provided it's appropriately sized, made of good-quality copper, and the connections to it are meticulously executed with proper torque specifications, hardware, and documentation. Focus on creating a robust, reliable, and well-documented grounding system.

Recommendation:

Before finalizing your design, it's always a good idea to consult with a qualified UL inspector or a UL-certified panel shop. They can provide specific guidance based on your application and help ensure your control panel meets all the requirements of UL508A. Even a pre-inspection consultation can save you time and money in the long run. You could show your drawing and components and ask them if everything is good.Good luck! Flag for review