Durability And Strength Of Plastic Electrical Boxes

- Mar 31, 2018-

This is where plastic junction boxes loose some points. Along with the box being plastic, the nail brackets are also plastic. They are easily broken off when installing a box or when you have to take a box off and reinstall one. Once this bracket clip is damaged or broken off, your mounting options are all but gone.

Also vulnerable are the two screw holes for installing a switch, outlet, or another device to the box. As with anything plastic, the threads inside the mounting holes are easily stripped if the screws are not installed properly. Quite often, you may be tempted to put any old screw into these holes, but the threads are usually set to a 6-32 thread. If the threads do become stripped, you may be able to still use the box by installing a short drywall screw into the hole--that is, if it isn’t cracked or damaged. The screw must hold the device firmly in place. 

When mounting light fixtures and ceiling fans, use metal boxes. Although there are some plastic boxes that are designed to support these fixtures, it’s hard to have faith in the plastic threads that support a fixture over your head. For heavy fixtures and all ceiling fans, be sure to use boxes with heavy-duty braces or mounting brackets designed for this purpose.



Plastic junction boxes aren't a good fit for the outdoors, and they can't be used with metal conduit, which is often required outdoors or when the wiring runs are not concealed inside wall or ceiling cavities. You can find "outdoor-rated" plastic boxes, but when you think about the effects of snow and ice and years of direct sunlight (the arch enemy of plastic), metal sounds like a much better bet.