When to Use a Plastic Electrical Box

- Mar 31, 2018-

Plastic (stiff polyvinyl chloride, or PVC) is fast becoming the standard material for electrical boxes. This material is lightweight, cheap, and simple to work with. Holes are easy to punch out in the back or sides. PVC can melt when subjected to high-enough temperatures but it does not conduct electricity. Many plastic boxes come with pre-attached clamps for the wires, lowering overall project cost.

Highly Recommended or Required

Use a plastic box when you have Romex Wiring leading in or out of the box. However, code dose not require that you use plastic with NM wires, only that the application be grounded.

Metal-sheathed wiring depends on bonding with the metal electrical box for grounding. Using metal-sheathed wiring with plastic electrical boxes severs that ground and is highly dangerous.

Other Considerations

Plastic electrical boxes are easy for do-it-yourself home renovators to work with.

The least expensive plastic boxes come with pre-attached nails for nailing into studs. Other boxes, called old-work or remodel boxes, have wings so they can be attached directly to drywall. Another set of boxes have metal brackets that attach to the studs but are adjustable in/out with a Phillips screwdriver.

These are the most expensive type but offer the most flexibility.

Many do-it-yourself electricians tend to find it easier to work with the plastic electrical box in conjunction with Romex or NM wiring. Plastic boxes are lighter and their holes are easier to knock out. Also, many plastic boxes have doors that act as clamps to hold the electrical cable to the box.

On the downside, plastic boxes have a tendency to become misshapen when stressed. When they receive a sharp blow, plastic boxes can crack. Remodel (old work) boxes attached to drywall can pull away from the drywall.