What are the correct dimensions for rectangular and round access openings for manholes?

The correct dimensions for rectangular and round access openings for manholes are specified in the National Electrical Code (NEC) and reflect the need for safe and efficient access for maintenance and inspections. The size chosen in option B, which includes a rectangular opening of 20 inches by 16 inches and a round opening of 20 inches in diameter, conforms to the standard requirements that allow personnel to enter and exit safely while providing enough space for tools and equipment.

These dimensions are designed to accommodate standard human dimensions, ensuring that workers can easily navigate in and out of manholes without risk of injury. Moreover, these sizes are also practical for the access of various tools that may be utilized within the manhole, facilitating work efficiency.

While the other options present various sizes for access openings, they do not meet the specified dimensions recognized within industry standards. Adhering to these dimensions is crucial for compliance with safety regulations and ensuring that any necessary inspections or maintenance tasks can be performed effectively.