How far above the floor must a vertically extended busway be enclosed to protect it from physical damage?

The correct answer is that a vertically extended busway must be enclosed at a height of 6 feet above the floor to provide adequate protection from physical damage. This requirement is outlined in the National Electrical Code (NEC), which emphasizes the need to safeguard electrical equipment, including busways, from potential mechanical impacts and other forms of damage that can occur in facilities where personnel and equipment may interface closely with electrical installations.

Enclosing the busway at this height helps ensure that it is out of reach of typical foot traffic and other activities that could lead to unintentional strikes, drops, or spills that might compromise the integrity of the electrical assembly. By adhering to this specification, electricians can maintain a safer work environment, preventing accidents and ensuring the longevity of the electrical infrastructure.

The specified height reflects industry standards and practices aimed at minimizing risks associated with physical damage to electrical components, which is why the choice of 6 feet is the appropriate answer. This height is generally regarded as sufficient to keep busways secure from common hazards found around floors in commercial and industrial settings.