Question: For outlet boxes that support ceiling suspended fans, does UL consider out-of-balance fans?
Answer: Section 422.18(a)
Section 422-18(a) of the 1996 National Electrical Code permits “listed” ceiling fans that do not exceed 35 lbs. to be supported by outlet boxes identified for such use. Ceiling fans exceeding 35 lbs. are required to be supported independently of the outlet box, in accordance with Section 422-18(b).
Requirements for ceiling-suspended fan support for metallic outlet boxes are located in UL 514A, the Standard for Metallic Outlet Boxes. For nonmetallic boxes, the requirements can be found in UL 514C, the standard for Nonmetallic Outlet Boxes, Flush-Device Boxes, and Covers. Both of these standards specifically include testing of the boxes using out-of-balance fans.
For the ceiling-suspended fan support test, a ceiling fan (weighing or ballasted to weigh 35 pounds) is installed in accordance with the manufacturer’s installation instructions. Samples are tested in both the horizontal position and at an incline of 30 degrees. A 40 gm (1.4 oz) weight (imbalance) is placed on a single fan blade and a rigid-metal pipe is connected to position the lower edge of the fan blade 12 inches from the ceiling. The fan is operated at a specified speed for 24 hours to simulate an unbalanced fan and then the outlet box is examined for damage. Next, one of the fan mounting screws is loosened two full turns, and the fan is operated for an additional 24 hours.
A UL listed outlet box intended to support a ceiling-suspended fan is required to be marked “Acceptable for Fan Support.”