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Replace a Switch or Outlet Safely: Testing, Wiring and Limits

Swapping a switch or outlet like for like is the most approachable electrical job in a house, but only after the breaker is off and two testers agree the circuit is dead. Here is the order, and where to stop.

Published 6 min read

A switch or outlet that you can touch is only safe once you have proved the circuit is dead. Everything in this guide is built around that one check. The wiring itself is simple, and it is the same few steps every time.

Before you start

  • Check the rules. In most jurisdictions homeowners may do their own electrical work, according to the Everyday Home Repairs video, which advises calling your local permitting office or electrical inspector to ask. Rules differ by place, and your permit office has the final word. See Do You Need a Permit?.
  • Turn off the right breaker. Ideally a labelled one. The Home Depot video tells everyone in the home that electrical work is under way, and suggests a sign on the breaker box so nobody switches it back on.
  • Test the tester. Check your non-contact voltage tester on a known live source first, then test the switches and the inside of the box (Everyday Home Repairs).
  • Use two kinds of tester. The Electrician U video says a non-contact tester only indicates the presence of power, cannot tell 120 volts from 240, and can be fooled, so it should not be the only way you verify. The This Old House electrician says to follow it with a contact tester before working. A multimeter set to voltage, or a simple plug-in or contact tester, does that.
  • Never work live. Electrician U says live work is only for trained people with the right protective equipment.
  • Use only electrical tape inside boxes (Home Depot).

Time, skill and cost

SkillBeginner to intermediate for a like-for-like swap. A different type of switch, or new wire, is a job for an electrician
TimeNot stated in the videos
CostOne video quotes a residential-grade switch at $1.88 at one store. Prices vary

Tools and materials

  • Non-contact voltage tester, multimeter
  • Screwdriver set, wire stripper, needle nose pliers
  • Replacement switch or outlet of the same type and amp rating, wire nuts that match the wire size on the package, electrical tape
  • A manual screwdriver is preferred to a drill-driver, since the screws are small and the space tight (Home Depot).

Step 1: Identify what you have

  • Wire gauge. In a cable labelled 14-2, the first number is the gauge and the second the number of wires; a smaller gauge number is a thicker wire. The Everyday Home Repairs video compares to coins: a nickel’s thickness is 12 gauge, a dime’s is 14.
  • Colours. Black is hot, white is neutral, bare is ground, and the red in a 14-3 cable is a second hot (Home Depot). Travelers in a three-way are usually black and red, but every install can differ.
  • Amp rating. Outlets come in 15 and 20 amp versions, the 20 amp having a T-slot. A 15 amp outlet can go on a 20 amp circuit, but a 20 amp outlet cannot go on a 15 amp circuit. The breaker is labelled 15 or 20.
  • Switch type. A single-pole (called two-way in that video) switch controls a light alone. A three-way has two travelers. Swapping a single pole for a three-way needs different wiring and often 14-3 cable, so the Home Depot video suggests an electrician.
  • A third hole does not prove an outlet is grounded (Home Depot).

Step 2: Prove it is dead

  1. Breaker off.
  2. Remove the cover plate. Score the paint seam with a razor blade first so the drywall paper doesn’t tear.
  3. Test with the non-contact tester. Green means dead and red means live in the Home Depot video.
  4. Confirm with a second tester. For an outlet, the Electrician U video checks hot to neutral (the video reads 126 volts in his commercial setting, with roughly 118 to 125 typical elsewhere), hot to ground (about the same), and neutral to ground (should be zero).
  5. Take a photo of the wiring before you disconnect anything.

Step 3: Swap the device

  • Loosen the screws and move one wire at a time so you do not mix them up.
  • Screw colours. Brass is hot and silver is neutral. Green is ground. Connect the ground first, in the same order every time (Electrician U).
  • Hook the wire clockwise around the screw, so tightening pulls it closed. Squeeze the loop so it stays on if the screw is loose. Don’t crush the wire.
  • Side wiring. The Everyday Home Repairs video recommends side wiring over the push-in “speed” holes, and does not mix the two. A speed-wired screw plays no part in holding the wire.
  • GFCI. The back of a GFCI is labelled line and load. Finding the line wires means separating the wires and briefly powering up, which the Home Depot video says to do with two people and with children and pets away. If you are not sure, hire an electrician. See GFCI Outlets: Where They’re Required and How to Test Them.
  • Dimmers. Wired the same way. A flickering dimmer may mean the bulb is not marked dimmable.

Step 4: Mount and test

  • Fold the wires back and seat the device flush with the drywall. Overtightening pulls it into the wall and the plate won’t sit straight; a loose screw leaves a gap (Electrician U).
  • Leave the mounting screws slightly loose until the plate is lined up, then tighten. Do not overtighten the plate screws, which can crack it.
  • Breaker on. Test the device. A three-light plug tester shows wiring faults. A pattern of on, on, off indicates reverse polarity, with black and white reversed. A reversed outlet still works, but the video calls it a safety hazard, because a lamp socket shell can stay live with the switch off. It is not for two-prong outlets.

Mistakes to avoid

  • Trusting a single non-contact tester.
  • Assuming a breaker label is right.
  • Forcing too many wires onto one screw.
  • Mixing 12 and 14 gauge wire without checking the circuit rating.
  • Fitting a 20 amp outlet to a 15 amp circuit.

Call a pro if

  • The breaker trips when you reset it. The Arnold Electric video describes a ground fault (a loose screw touching a metal box) and a short circuit (hot and neutral touching) as faults where the breaker trips the instant you reset it. Don’t keep resetting it.
  • The tester shows power with the breaker off, or you can’t tell which breaker feeds the box.
  • You need new wire, a new circuit, or you are converting a single-pole to a three-way.
  • The wire is aluminium, cloth-covered or brittle, or the box is burnt. We have no video on those.
  • Your permit office says the work needs a licensed electrician.

Learn more

Sources

  1. Shown on this site, source of the three-tester method and the mounting advice. Replacing a Receptacle Safely: Testers, Wiring and Mounting (video, Electrician U) Source
  2. Shown on this site, source of the wire, screw and amp-rating guidance. Replacing Switches and Outlets: Wire Colors, Screws and Safety (video, The Home Depot) Source
  3. Shown on this site, source of the side-wiring method and the permit advice. Replacing a Two-Way Light Switch: Safe Side Wiring Step by Step (video, Everyday Home Repairs) Source
  4. Shown on this site, source of the tester limits and polarity check. Three Voltage Testers and What Reverse Polarity Does to a Lamp (video, This Old House) Source
  5. Shown on this site, source of the tripping causes. Why Breakers Trip: Overloads, Ground Faults and Short Circuits (video, Arnold Electric) Source

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