Electrical knockout boxes with combination layouts provide separate areas for power and low-voltage wiring within one wall opening, helping keep the installation neat and organized. Retrofit designs can mount in existing drywall or paneling, while built-in knockouts and adjustable features help accommodate conduit, cables, and varying wall thicknesses.

Before installing an electrical knockout box, check that the retrofit wallboard or paneling is between 1/4 inch and 1 1/5 inches thick and that the opening can accommodate the box. Confirm that the mounting surface supports the box’s screws and spring clip, and verify that the available 1/2-inch or 3/4-inch knockouts match the wiring setup.

Nonmetallic electrical knockout boxes can provide a faster retrofit option for two-gang applications because one-piece designs do not require box assembly and attach to the wall with mounting screws and a spring clip. They can also combine power and low-voltage wiring in one installation, while knockout options support common conduit sizes such as one-half inch and three-quarter inch.

Compare the available 1/2-inch and 3/4-inch knockouts with the conduit or cable-entry fittings you plan to use. Also compare the box’s 4-by-4-inch dimensions and interior space with the device, wiring, and back-box requirements for the installation.