The world of electrical boxes can feel overwhelming in terms of sizes, materials, and purposes. So for the beginning do-it-yourself electrician, it can be helpful to break down electrical boxes into two categories: old work electrical boxes and new work electrical boxes.
Old work boxes help you retrofit into an existing wall, without having to tear out more drywall or plaster than is necessary. New work boxes are for open studs, where the wall system is visible and there is no drywall or plaster.
Old Work Electrical Box
Old Work or Remodel Electrical Box
Sometimes called a remodel box or retrofit box, an old work electrical box can be inserted into an opening in the wall covering. The box attaches directly to the covering, not to the studs. It is used when remodeling rather than when constructing new wall systems. An old work electrical box is the only way to add a box to an existing wall without tearing out a significant portion of that wall.
An old work box is an electrical box for light switches, outlets, and other devices that are installed after drywall has been installed on the wall studs.
The term old work (sometimes old construction or retrofit) refers to walls that are already covered up, making it impossible to access the studs. Thus, old work electrical boxes attach directly to the wallboard.
Old work plastic electrical boxes slide into wallboard cut-ins, then are held permanently in place with plastic tabs that spread outward when turned clockwise with a Phillips screwdriver.
Old work boxes' plastic tabs are prone to breakage. Additionally, the Phillips screws that control the plastic tabs tend to be made of soft metal, making it difficult to screw them tightly in place.
Old work electrical boxes ideally are placed in the center of wall cavities or at least nearby. They cannot be placed against wall studs because the wings that hold the boxes to the drywall need a couple of inches to extend outward.
Retrofit established walls
No need to remove drywall
No need to pre-cut drywall around boxes
Often poor attachment to drywall
Box mechanism can be flimsy
Cannot be hung against studs
New Work Electrical Box
New Work Electrical Box
The term new work (sometimes new-construction) refers to walls that have not yet been closed in with wallboard. Because the framing is exposed, it is possible to nail or screw these new work electrical boxes to the sides of the studs.
New work boxes require full access to the stud. It is exceedingly difficult, if not impossible, to attach a new work box through a pre-cut hole in the drywall and to the stud. Several square feet of drywall must be removed first, then the box must be nailed or screwed to the side or face of the stud. Finally, drywall must be cut to fit the section.
If the wall system is open, it is preferable to use new work electrical boxes rather than installing old work boxes post-drywall installation. The bond is considered to be more secure than attaching to the drywall. Electrical code provides for both old work and new work boxes.
A disadvantage of nail-in plastic boxes is that, unless nailed carefully, they can warp, twist, or misalign. Additionally, the tabs in the back are supposed to partially punch out, acting as clamps. But these flaps are a poor substitute for true wire clamps of the type that are attached to metal boxes.
Allows you to establish layout of boxes before walls are hung
Can be adjusted (when using adjustable work boxes)
Requires open wall
Can warp or twist if nailed incorrectly
Can be difficult to cut drywall around boxes
Plastic vs. Metal New Work Boxes
Metal boxes have been around for a long time. Metal boxes are mostly used with metal-clad cable. Plastic boxes are easier for beginners to handle and can be cheaper. Generally, try to use plastic boxes with plastic-clad wiring. This type of wiring is also known under the brand name Romex or the generic term NM.
When stability is important, you will have no better feeling of security than when you can screw in a metal new-work electrical box. This type of box will absolutely stay in place under most conditions. Metal new-work boxes often have built-in back clamps for holding down the wire.
Electrical boxes composed of ASB plastic or fiberglass are used with NM wire. Besides low cost, another advantage of plastic boxes is that they are light and easy to handle.
Plastic boxes can be quite brittle. An errant swing of the hammer can shatter a plastic box, even though box manufacturers like to claim that their products are shatter-proof.
Adjustable New Work Boxes
It is possible to purchase either metal or plastic new-work electrical boxes with a mechanism that adjusts the box in or out of the wall. The idea is to provide flexibility so that the face of the box will come flush with the wallboard merely by turning a screw, rather than digging into the wall and reattaching.
Adjustable new work boxes are critical if the eventual thickness of the wall has yet to be determined. One example of this is when a new work box is installed with drywall, but another wall covering, such as paneling or wainscot, may be added on top of the drywall.