What is the minimum clearance required between the top of a switchboard and a combustible ceiling when there is no noncombustible shield?

The minimum clearance required between the top of a switchboard and a combustible ceiling is 36 inches. This clearance is crucial for safety reasons, as it helps to prevent overheating and potential fire hazards resulting from heat buildup and electrical arcing, which can occur near electrical equipment such as switchboards.

The National Electrical Code (NEC) outlines clearance requirements to ensure adequate space for both operations and maintenance, as well as to reduce the risk of ignition of combustible materials. A clearance of 36 inches allows for sufficient air circulation around the equipment, minimizing the chances of it overheating.

Clearances greater than this, while they may provide additional safety, are not the minimum required as per the current standards, making 36 inches the most relevant answer in this context.