Se a caixa foi instalada recentemente de acordo com o National Electrical Code (NEC), a caixa deve ser rotulada se for classificada para suportar um ventilador de teto.
NEC 2008
314.27 Outlet Boxes.
(D) Boxes at Ceiling-Suspended (Paddle) Fan Outlets. Outlet boxes or outlet box systems used as the sole support of a ceiling-suspended (paddle) fan shall be listed, shall be marked by their manufacturer as suitable for this purpose, and shall not support ceiling-suspended (paddle) fans that weigh more than 32 kg (70 lb). For outlet boxes or outlet box systems designed to support ceiling-suspended (paddle) fans that weigh more than 16 kg (35 lb), the required marking shall include the maximum weight to be supported.
Se não estiver etiquetado, a caixa ainda é necessária para suportar pelo menos 50 lbs.
314.27 Outlet Boxes.
(A) Boxes at Luminaire Outlets. Boxes used at luminaire or lampholder outlets in a ceiling shall be designed for the purpose and shall be required to support a luminaire weighing a minimum of 23 kg (50 lb). Boxes used at luminaire or lampholder outlets in a wall shall be designed for the purpose and shall be marked to indicate the maximum weight of the luminaire that is permitted to be supported by the box in the wall, if other than 23 kg (50 lb). At every outlet used exclusively for lighting, the box shall be designed or installed so that a luminaire may be attached.
Se a caixa foi instalada antes deste código ser adotado; ou em uma área que não segue a NEC, você provavelmente terá que cortar / perfurar alguns orifícios exploratórios para determinar se a caixa está devidamente preparada.