Metallic boxes can be used with either nonmetallic (throw in NM-B) or metallic sheathed electrical cable.

Nonmetallic plastic boxes are designed for use only with nonmetallic sheathed electrical cable.

An old work box is designed to be installed after the facton walls that are already finished.

Old work electrical box being mounted into wall with screwdriver

The Spruce / Kevin Norris

Prepare the Box’s Cable Clamp (PVC Boxes Only)

Open up the clamping tab.

These clamping tabs can be a little difficult to open up.

This will loosen the clamp and make it easier to insert the cable.

Materials and tools to install an old work electrical box

The Spruce / Kevin Norris

Prepare the Electrical Box Opening in the Wall

Create the wall cutout.

Position the electrical box backward against the wall, in the exact position you plan to install it.

Use a utility knife to score the wall along the shape you outlined.

Retention tab screw tightened into old work electrical box with screwdriver

The Spruce / Kevin Norris

Using a drywall keyhole saw, carefully cut the hole along the traced outline and remove the drywall blank.

If so, this will become apparent when you venture to slide the box into the wall.

More complicated wiring scenarios may call for two cables.

Old work electrical box clamp tab pushed open with flat-blade screwdriver

The Spruce / Kevin Norris

check that the new lengths of cable are sized appropriately for the amperage of the circuit.

There should be 8 to 12 inches of excess cable at the new wall opening.

At this point, the new cable should be unattached to any electrical devices.

Outline of old work electrical box drawn with pencil on wall with level

The Spruce / Kevin Norris

Carefully cut the sheathing off.

see to it to leave about 6 to 7 inches of exposed wires.

If you use a utility knife to strip wires, verify not to nick the metal conductors.

NM-B electrical cable run through box opening in wall

The Spruce / Kevin Norris

Your box is now ready toreceive an outlet receptacle or switch.

An old work electrical box goes in after drywall is already up.

A new work electrical box is installed prior to drywall once the walls are framed.

Old work electrical box inserted into wall opening with stripped cable

The Spruce / Kevin Norris

Old work electrical boxes use retention tabs plus mounting ears.

They tighten against the front and back of the drywall to hold the box in place.

Read the manufacturers label carefully to be sure you have the right box.

Old work electrical box mounted to wall opening with screwdriver

The Spruce / Kevin Norris

Wire insulation stripped from wire end conductors

The Spruce / Kevin Norris

Wired ends covered with nut caps before final connections

The Spruce / Kevin Norris