What is the minimum fire rating for electrical vaults housing electrical equipment over 600 volts?

The minimum fire rating for electrical vaults housing electrical equipment over 600 volts is established based on the need for safety and fire protection in buildings. A three-hour fire rating helps ensure that in the event of an electrical fire, the vault can contain the fire for an extended period, allowing for safe evacuation of occupants and providing sufficient time for firefighting efforts. This extended duration minimizes the risk of fire spreading to adjacent areas, which is crucial when dealing with high-voltage electrical equipment that has the potential to cause significant damage and presents safety risks.

A one-hour or two-hour fire rating, while helpful, may not offer adequate protection for the higher energy densities and potential fire hazards associated with equipment operating above 600 volts. The four-hour rating, while also beneficial, is more stringent than what is typically required, making three hours the appropriate standard for balancing safety requirements and practicality for electrical vaults in this context.