Yes, NEC 2017 allows welding as a means of bonding a ground bus (likely a grounding busbar or neutral busbar, depending on its function) to the panelboard enclosure, provided certain conditions are met.

Here's a breakdown of the relevant considerations: NEC 250.8 Connections, Bonding

This section is the key. It lists acceptable methods for making bonding connections. While it doesn't explicitly mention welding, it does say connections must be made by: "(1) Exothermic welding (2) Listed pressure connectors (3) Listed clamps (4) Other listed means."Since welding is mentioned as a possible means of making connection, it can be used as a mean of bonding.

Importance of Proper Welding

The quality of the weld is paramount. It needs to be a sound, electrically continuous connection. A poor weld won't provide a reliable low-impedance path for fault current.

UL Listing and Standards

Panelboards are typically UL listed. The manufacturer's instructions and the UL standard the panelboard is listed to (e.g., UL 67) will dictate what is acceptable. Welding is most likely permitted if it was part of the original design and UL listing of the panelboard. Modifying a listed panelboard by welding without the manufacturer's approval could void the listing.

Professional Practices

Best practice is to follow the manufacturer's instructions, and avoid welding to listed equipment unless it is clearly allowed by the instructions.

In Summary

Welding can be an acceptable method of bonding a ground bus to a panelboard enclosure under NEC 2017, BUT:1.

The weld must be high-quality and provide a reliable, low-impedance path.2. It's best if the welding is performed at the factory3. If adding the welding after the fact, it must be approved by the manufacturer for the specific panelboard.4. Field welding can void the panelboard's UL listing if it's not in accordance with the manufacturer's instructions and UL standards.Therefore, review the manufacturer's documentation for the specific panelboard. If there is nothing about it, consult the manufacturer's engineer before making any decision.

I am an AI chatbot and cannot provide professional engineering advice. Consult with a qualified electrical engineer for definitive guidance on your specific project. Flag for review