When To Use A Plastic Or Metal Electrical Box?

While there is an abundance of sizes, shapes, and attachment variations with electrical boxes, all of them fall into two categories: plastic boxes or metal boxes.

Sometimes, the choice is one of personal preference, economy, and ease. In a few cases, though, the choice is clear-cut and obvious, mainly with respect to grounding. Generally, do-it-yourselfers prefer plastic electrical boxes and electricians use both metal and plastic boxes.

When to Use Plastic vs. Metal Electrical Boxes

Use plastic electrical boxes or metal boxes for any of these situations.

Use a plastic electrical box for

● NM or Romex plastic sheathed wires leading in or out of the box

● Grounding is independent of the box

● Old work or remodel box installation that attaches to the drywall, not the studs

● Old work or remodel box installation that attaches to the drywall, not the studs

● Open walls where the thickness of the wall covering is still undetermined (for use with adjustable plastic boxes)

● Do-it-yourself electricians

Use a metal electrical box for

● Metallic sheathed or BX wire

● Grounding depends on the box

● Exposed locations (where the box is not set into the wall)

● Stud attachment rather than drywall attachment

● Gangable installations where boxes need to be connected

● Installations that create heavy strain on the box

● Experienced do-it-yourself electricians

Metal Electrical Boxes

Metal electrical boxes were used long before plastic (PVC) electrical boxes were introduced to the market. Ultra-strong, fireproof, and incapable of being melted, metal boxes offer the greatest level of security for all electrical wiring applications.

Even when slightly stressed, plastic boxes can twist. With enough stress, plastic boxes will distend. Even hammering the plastic box to the stud the wrong way can twist the box out of shape. Metal electrical boxes have no such problem: It is virtually impossible to bend or crush metal electrical or junction boxes.

For do-it-yourselfers, metal electrical boxes can be slightly more difficult to work with. Metal boxes have rear and side knock-outs that require supplementary clamps. In addition, metal boxes' sharp edges can take a toll on hands. For this reason, it is recommended that you wear gloves when working with metal boxes.

Plastic Electrical Boxes

Plastic (made of polyvinyl chloride, or PVC) is fast becoming the standard material for electrical boxes, especially for do-it-yourself work

Plastic boxes are lightweight, cheap, and simple to work with. Holes are easy to punch out in the back or sides. PVC can melt when subjected to sufficiently high temperatures but it does not conduct electricity. Many plastic boxes come with built-in clamps for the wires, further lowering the overall project cost.