NEC Commercial Electrical Practice Test

The correct designation for the masonry wall opposite the switchboard in a room with a 480 volt switchboard is "Grounded." According to the National Electrical Code (NEC), the requirements and provisions related to switchboards designate that specific types of walls should have grounding characteristics to ensure safety and compliance with electrical standards.

Having a grounded wall helps to establish a defined reference point for the switchboard system and provides necessary safety measures to protect against electrical faults. This wall effectively acts to minimize the potential for electrical shock or fire hazards by ensuring that if there is a fault, the electrical current can properly dissipate to ground.

The other designations like "Non-grounded," "Exterior," and "Load-bearing" do not specifically relate to the electrical safety and functional criteria described by the NEC for switchboard proximity. Non-grounded would suggest a lack of proper grounding, which is not suitable for the functionality of high-voltage equipment. Exterior refers to walls that are outside the conditioned space, which does not relate to the grounded concept. Load-bearing pertains to structural integrity rather than electrical safety, which is not the primary concern when selecting materials or designations for walls housing electrical equipment.