What is the minimum distance that must be provided between the top of an unshielded switchboard and a combustible ceiling?

The minimum distance required between the top of an unshielded switchboard and a combustible ceiling is 36 inches. This regulation ensures that there is adequate space to prevent potential overheating and ignition of combustible materials due to heat and electrical arcs that could occur with the operation of the switchboard. The presence of this clearance is critical for maintaining safety standards and reducing the risk of fire hazards in electrical installations.

By providing this specific distance, it also allows for proper ventilation around the switchboard, which helps in dissipating heat generated during normal operation. This clearance is a part of electrical safety codes aimed at protecting both equipment and structures. Thus, the answer reflects established safety practices within the electrical industry.