Final answer:
A box must be labeled as able to support the weight of a ceiling fan, typically at least 70 pounds, according to the NEC. It is important to use a fan-rated box that is UL-listed for safety and compliance with code requirements.
Step-by-step explanation:
To ensure safety and proper installation, a ceiling fan must be supported by an appropriate ceiling box that is labeled as being able to support the weight of the fan. The National Electrical Code (NEC) specifies that ceiling fan boxes must be able to support at least 70 pounds. Therefore, the box must have a label indicating it can support the weight of the ceiling fan. It's crucial to use a fan-rated box and not just a standard ceiling box, as the latter is designed only to support lightweight fixtures and not the dynamic loads generated by ceiling fans. For the installation of ceiling fans, an ul-listed fan-rated box is recommended to ensure that it meets safety standards and code requirements.