A 4,000A switchboard requires a minimum distance from the phase bus to the closest steel member of?

The minimum distance from the phase bus to the closest steel member in a switchboard, especially for a 4,000A switchboard, is critical for ensuring proper spacing for both safety and operational efficiency. The requirement of a minimum distance of 6 inches (150mm) helps prevent issues related to potential arcing, electromagnetic interference, and ensuring adequate cooling of the bus conductors.

Maintaining this distance is crucial because if the phase bus is too close to any metallic surfaces, it can result in safety hazards, including electrical shorts or failures that may arise from accidental contact or proximity. Additionally, the specified distance is designed to allow for sufficient access for maintenance and inspections without risk of electrical hazards.

This level of clearance is often aligned with industry standards and codes, which dictate distances to adequately manage these risks while ensuring the functionality of the electrical distribution equipment. In this context, the other distance options either do not align with these standards or exceed the requirements, making 6 inches the most appropriate and compliant choice.