How to Replace Electrical Boxes Behind Drywall

Introduction

Replacing electrical boxes that are hidden behind drywall can seem daunting, but with the right tools and patience, it is very doable as a DIY project. Electrical boxes house outlets, switches, and fixtures, so maintaining and replacing them is an important part of home maintenance. In this comprehensive guide, I will walk through all the steps I take to safely replace electrical boxes that are buried behind drywall.

When to Replace Electrical Boxes Behind Drywall

There are a few situations that would require replacing an electrical box behind drywall:

Upgrading to a larger box - If you need to fit more wires in a box due to adding circuits or switches, you may need to install a bigger electrical box.
Damaged box - Electrical boxes can become damaged over time. If the box itself is compromised, with cracks or other defects, it's safest to replace it.
Grounding issues - Older electrical systems may not have a grounding wire. Replacing with a grounded electrical box brings things up to code.
Insufficient box depth - Electrical codes require boxes to be deep enough to allow room for wires and devices. Replace shallow boxes.
Removing unwanted boxes - If you are remodeling and want to remove unused, obsolete electrical boxes, replacing with a blank cover maintains the fire rating of the wall.

Preparing for Electrical Box Replacement

Before I start replacing a box, I make sure to take a few important steps:

Turn off power - The circuit must be shut off at the breaker before working. I double check with a non-contact voltage tester. Safety first!
Identify the circuit - I figure out which breaker controls the box I'll be replacing. Testing with a multimeter helps verify.
Gather supplies - I assemble all the tools and materials I will need, including new electrical box, drywall saw, screwdrivers, hammer, wire strippers, etc.
Take photos - To help with reassembly, I take photos of the wires, noting wire colors and terminal positions.
Inspect wires - I check that the existing wires are in good condition, not deteriorated or damaged. I replace any suspect cables.

Removing the Existing Electrical Box

With the prep work done, I can start removing the old electrical box:

I use a drywall saw to cut through the drywall around the box, so I can access the entire thing. I cut out a square large enough to work in.
I unscrew the box from any braces or studs it is attached to and carefully pull it out from the drywall opening.
If wires are clipped to the box, I detach them one at a time while supporting the box so it doesn't fall back into the wall.
I gently pull the wires out and temporarily position them out of the way, using wire nuts to cap any exposed wire ends.
If there is insulation or vapor barrier, I may need to cut it back from the open hole temporarily.
Lastly, I vacuum up any drywall dust or debris left from cutting open the wall.

Installing the New Replacement Electrical Box

With the opening prepared, it's time to mount the new box:

I measure the hole size and mark reference lines to center the box.
Electrical boxes have knockouts that I remove as needed for the required number of wires.
I feed the wires into the box one at a time, taking care not to loosen wire connections.
Holding the electrical box centered in the opening, I secure it using screws anchored to the studs or drywall braces.
If the box needs to be grounded, I connect the ground wire to the green screw or terminal in the box.
I double check all my wire connections by referring to my photos, and secure the cables tightly to the box.

Patching the Drywall Opening

Now I just need to patch up the drywall:

I cut a piece of drywall to fit the opening, either using leftover pieces or a patch kit.
After dry fitting the patch piece, I mix up drywall joint compound and apply it around the edges, securing the patch in place.
In thin coats, I cover all seams and screw holes, allowing time for it to dry completely between applications.
When the joint compound is built up and smooth, I carefully sand until the seams blend with the surrounding wall.
Finally, I prime and paint the sanded patch to match the existing wall color. Once the paint is dry, the repair is complete.

Finishing Up the Electrical Box Replacement

To wrap up the project:

I turn the circuit breaker back on and test that the box is powered.
I install the outlet, switch, or other device into the box.
Lastly, I securely screw the cover plate in place.

Replacing an outdated or damaged electrical box is very doable with some handy DIY skills. Carefully following safety procedures makes the process straightforward. Taking a methodical approach ensures the new box is properly installed and secured for years of safe electrical service.