How about the octagonal junction box and how to use it?

Octagonal electrical box is a common type of box, which is usually used to install lamps on walls or ceilings. They are usually made of metal, with standard dimensions of 4 x 4 inches and depths of 1-1/4, 1-1/2 and 2-1/8 inches. Octagonal boxes are not really octagons - they are more like squares with bevels or shears. This shape is more suitable for matching with the round base of the lamp than the square box, so that it is easy to hide the box when installing the lamp. Octagonal boxes have several different applications.

Standard octagonal box

The standard octagonal box is an ordinary metal box, which can be directly installed on the wall or ceiling frame (wall nail or ceiling or floor joist) with wood screws. Some have brackets for mounting to the sides of studs or joists. If the box is located between two frame members, the standard box can be installed on a solid wood block installed between the members. In this case, the back of the box is placed flat on the stop and fixed with at least two screws. If the box is properly rated and the screws are strong enough, this can provide a safe connection for heavy lamps and even ceiling fans.

Support box

The octagonal box with support has adjustable metal support or rod, which can extend outward to connect with the frame members on both sides of the box, allowing installation anywhere between the two frame members (using the alternative method of wood blocking). They are most often used with ceiling fixtures, but they are also suitable for wall mounted lighting. The bracket is usually fixed to the frame with screws. Some heavy brackets have integrated mounting devices, which drive the bracket into the frame through screw devices similar to pistons.

New and old workboxes

If a box is marked "new work", it is a standard type designed for installation during a new building or renovation where the wall or ceiling gypsum board has not been suspended and the frame is fully exposed. The "old work" (sometimes referred to as "retrofit") box has a special installation device that allows you to install the box when the gypsum board is already in place. Standard old work boxes usually have mounting lugs that secure the box to the gypsum board when you tighten it. The support box of the old work has a spiral piston device on the support, so that you can fix the box without cutting a big hole in the gypsum board.

Rated load

The rated load is the weight that the box can safely support. It is important to use boxes of appropriate rating for each fixture and install boxes and fixtures as designed. A standard octagonal box may have a weight rating of up to 35 pounds (depending on the installation method), while a box with a light support may have a weight rating of only 10 or 15 pounds. The heavy ceiling fan box can be rated at more than 50 pounds. Do not install the ceiling fan on the standard octagonal box; You must use boxes (and brackets) designed for ceiling fans.