How to Locate Electrical Wires Behind Sheetrock

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  • 4 hours
  • Intermediate
  • 85
What You'll Need
Multi-scanner with AC option
Live circuit tracing kit
Spare batteries
3/8" or 1/2" drill bit
Drill
Utility knife
Pencil
Cordless drill (optional)
Cordless power saw (optional)
handsaw (optional)
Battery operated trouble light (optional)

Sooner or later, most DIYers find themselves installing a new window, cutting out an opening for a door, or drilling holes through hollow walls to mount pictures, shelves, or grab bars. In moments like these, it's critical to know about plumbing or live wires inside the walls. Hitting a wire under sheetrock with a saw could result in nasty damages or injuries. Careful planning, therefore, is always a priority.

Step 1 - Gathering the Proper Detection Tools

Nowadays, there are several tools available to detect what’s behind or inside the walls in the house. They are as versatile as their price range with the most affordable multi-scanner to the less known wall/floor radar scanner. But whatever tool is chosen, it must be able to detect live wires, which requires specialized technology.

The electronic multi-scanner in Figure 1 must be capable of detecting electric wires.

A live circuit tracing kit like the one in Figure 2 with a transmitter that can insert a signal in the line and a receiver that picks up the generated tones, and making it possible to track and locate live wires through various materials is available in the $250 price range.

wall scanners

The wall/floor Ultra-Wide Band Radar Scanner that can read almost anything beyond the wall surface has a price tag from around $1000 (Figure 3).

radar wall scanner

Step 2 - Wires through Wallplates

If the breaker panel is in the basement, it’s likely that the wiring to any of the circuits going through that area will come from the basement through the bottom wall plate.

If it’s accessible from an unfinished basement or a suspended ceiling in the basement, the location of the section of the wall to be altered can be established from the basement, looking up as in Figure 4.

the electrical cables from the basement are passed through the wallplate of the wall above to feed an outlet or fixture.

If the main electric panel is on the first floor, however, most of the cables will be directed through the ceiling and into the attic where they will then be routed to specific areas and dropped down through the proper walls below to their bound outlet terminal box.

In either of those two cases, if there is possible access to see and follow the routing of the implied cables, it’s likely that they can be traced back to the panel.

Step 3 - Looking for Outlets Nearby

With no obvious cables running vertically, the walls in the immediate surroundings should be visually scanned for outlets and switches on both sides of the walls, this being a tell-tale if there are cables inside running horizontally through the studs in the walls.

And if light switches are present with no cables routed through the top or bottom wall plates, it is very likely that they tap their power from a junction box or an outlet nearby.

Step 4 - Tracking with the Circuit Tracing Kit

Using the live circuit tracing kit, when the transmitter unit is plugged into the closest outlet to the area of interest, the scanner probe is moved along the wall starting from where the transmitter is plugged-in while following where the sound and LED signal strength indicator on the probe leads it. The receiving probe can have a range of three feet or more, making it easier for overhead wiring.

Step 5 - 3-in-1 and 4-in-1 Stud Finders

A reliable Multi-Scanner with the ability to scan wood, metal, wire, and pipes or any three combinations including wire, can be purchased for around $65. This tool will also detect any live wire running through the wall with a sharp beeping sound while the electrical LED would indicate a live wire (Figure 5).

diagram of wall scanner

Step 6 - Calibrating the Multi-Scanner

New or freshly charged batteries should be installed in the device. Most stud finders need to be calibrated before use by placing it flat on the wall and hold in the power button for a few seconds while it calibrates itself to the wall’s surface. If the tool starts beeping intermittently with a light flashing in some models, it is because of either a calibration error or is placed over a stud. With the Stud Finder moved over a few inches to the right or the left, the process must be repeated again.

Step 7 - Scanning the Wall

Once calibration is achieved, the search can be started on one side of the delineated area to be cut out or the spot to drill through. By pressing the stud finder power button and gradually moving it slowly across the area, a stud, a pipe, or a wire inside the wall will trigger a beeping signal, which one will be confirmed with an indicator light in Figure 6 flashing on the scanner.

The whole area should be scanned left to right and from top to bottom and if a wire shows, it should be marked all the way up, or all the way across, to avoid damaging it when cutting or drilling.

wall scanner device

Step 8 - Safety Measures

If the wires needed to be live while using scanners and probes, once it is determined that there are wires in the wall, the power MUST BE TURNED OFF at the circuit breaker before proceeding with power tools to alter the wall itself. Once the blade from a power tool grabs a wire, it will be severed before you know it, causing a high risk for fire or personal injury.

If someone should proceed to the next step nine because there is serious cause to believe a wire is present, the circuit breaker again must be switched off as soon as this is determined, but if it’s not possible to locate the right breaker, the main breaker from the electric panel must be switched off, leaving the work to be done relying on a flashlight and cordless or hand tools until the wire is disabled and secured in some way and out of the way.

Step 9 - Alternative when Sectioning the Wall

If the sectioning off part of the wall is in the process, another way around the issue of electrical wires should tracers or scanners not be available is by using a drill and a 3/8” or 1/2” (9 or 12 mm) drill bit. After getting everything ready, the approximate size of the opening is traced on the wall.

Using the drill and one of the bits, drill four shallow holes through the drywall, just going through without dropping farther inside. The blade of a large screwdriver can be inserted in each hole and move around as far as possible, to feel for obstructions inside the wall, such as electrical, plumbing, or construction blocks.

Step 10 - Getting a better view

A utility knife can be used to enlarge both of the top holes about 6” to 8” to get a better feel and view and confirm that nothing is in the way, or if it is, can be dealt with later on without cutting off or damaging anything at this time. More openings can be added as required. Once the wall feels safe to work at and the process under control, the work can be completed.