Plastic or Steel Cable Boxes?

Both plastic and steel boxes are used in residential construction. A box has to withstand a certain amount of construction trauma when it’s installed and later when drywall is installed around it. (Drywall hangers are not necessarily kind and gentle people, at least not when they’re getting paid by the square foot.) Plastic boxes are lightweight and are easy to install, especially those that come with nails for direct attachment to a wall stud or a floor joist.
Metal boxes are standard in most commercial work. Unlike a plastic box, a metal box is a good conductor of electricity and must be grounded along with the device or fixture. Special fittings are used to connect a metal box to conduit and conductors to the box. These fittings include an array of clamps, clips, and locknuts, most of which you’ll never use in the course of residential repairs and remodeling. A plastic box works well for a single gang or device use, but some electricians find that a larger plastic box’s shape distorts during installation or when the drywall is installed. For these reasons, they use tougher boxes, either Bakelite (reinforced phenolic) or metal for two gang installations and metal for three gang. The larger the box, the more difficult it is to keep it level and in line.