Recently had situation where I had to install a couple of commercial type ceiling fans. They were made by Dayton and did not mount to a standard ceiling fan junction box. Instead they were to be mounted using a lag bolt with an open hook the only way to install them with the boxes available were to use fan approved boxes and drill out 1/4" hole to a 3/8 hole in the box. (The box is supported by a U bolt around deep strut and the hook is bolted to the strut)
The other option would have been to use 4-0 box and knock out a 1/2" knockout with oversized washers. I chose the fan approved boxes since they seem a little more heavy duty.
What would you have done?
Wirewiz
