14 Common Mistakes DIYers Make With Electrical Projects
Updated: Jul. 25, 2024
When it comes to electrical projects, it's always safety first.
Working on your own home is empowering and saves you money. Electrical projects require a special level of precaution, though, and as you’ll see below, even a licensed electrical like myself can have some skeletons in her closet. Here’s how to avoid these common DIY mistakes.
Using a Non-Contact Voltage Tester Incorrectly
Electricians always carry non-contact voltage testers with them, and you should have one, too. They’re inexpensive and easy to use, but if you don’t do it right, what’s the point? Here’s what to do:
First, verify that the tester works by checking a known live circuit. Hold the tester to a powered appliance or lamp cord, or insert it into a receptacle (use the smaller slot, which is the “hot” side). If it doesn’t light up and/or beep, change the batteries and test again. When you know the tester works, locate and turn off the circuit at the breaker and verify it’s off with the tester.
Before putting the tester back in your pocket and before you start touching the dead circuit, test it again on the same live circuit as before. This will ensure that your tester didn’t malfunction while you were using it. Remember: Test, Use, Test.
Cutting Wires Too Short
Trying to connect together, aka splice, tiny little wires in an electrical box is difficult, and any resulting bad splice can cause electrical arcs and fires. That’s why the National Electrical Code (NEC) requires six inches of “free conductors” at every electrical box. But even if you start with plenty of length, conductors tend to get shorter as people swap out devices over the life of a home.
To remedy this situation, add a pigtail, which is a short piece of wire used to extend an electrical connection. To make splicing easier, use a push-in connector or lever nut, aka Wago, rather than trying to spin on a traditional wire nut.
Using the Wrong Size Wires
The diameter of electrical wires, also known as their “gauge,” determines how much current they can safely carry. Using too-small wires causes overheating, but unnecessarily large wires are a waste of money. When doing DIY electrical work, it is important to match the right size wire to the circuit.
Depending on the age of your home, you’ll likely see 20-amp circuits in your kitchen, bathroom and laundry room and 15-amp circuits in bedrooms, living rooms, hallways and elsewhere. The circuit breaker tells you the size of the circuit. Use 14-gauge wire for 15-amp circuits and 12-gauge wire for 20-amp circuits. Other loads, like electric stoves and dryers, furnaces and other large equipment, need bigger wires.
Electricians spend years learning the nuances of sizing wire for specific electrical loads, so if you have any doubts about what goes where, call a licensed pro.
Not Using GFCIs and AFCIs
Ground-fault circuit interrupters (GFCI) protect people from electrical shock. Arc-fault circuit interrupters (AFCI) protect your home from fires. Both are required by the NEC in various rooms and circuits in your home, depending on the particular NEC code cycle in place when your house was built.
In general, use GFCI protection in bathrooms, kitchens, laundry rooms, basements, outdoors and other locations where water is likely to be present. As for AFCIs, the NEC started requiring them in bedrooms in 1999 to protect sleeping people from fires. Since then, the list has grown to nearly every room in your house (except bathrooms and garages). Consult your local electrical code authority for specifics.
Both AFCI and GFCI protection can be provided by breakers or receptacles. If using a receptacle, it must be placed in the first outlet after the panel, and wired correctly, to protect other receptacles downstream.
Using Too Many GFCIs and AFCIs
Just because the NEC requires GFCI and AFCI protection doesn’t mean you have to buy multiple individual GFCI and AFCI receptacles to install in every outlet. It’s okay to use one receptacle installed in the first outlet or a breaker to protect an entire circuit.
Once, a friend needed help with a bathroom receptacle that wasn’t working. It was not a GFCI receptacle, even though GFCI protection is required in bathrooms. Had the electrician who wired her house screwed up? Nope, I assured her as I climbed to the upstairs bathroom. There, I found a tripped GFCI and reset it. The downstairs outlet now worked, and the installation was perfectly legal.
To check whether your circuits are GFCI protected, purchase a GFCI tester, available at any hardware store or home improvement center.
Recessing Boxes Behind Wall Surfaces
To help prevent the spread of fire, the boxes containing your light switches and receptacles should be flush, or nearly flush, with the finished surface of the wall. In tile, drywall and other noncombustible materials, boxes can sit back one-quarter of an inch, while they must be exactly flush with the surface of wood paneling and other flammable walls.
If you put up a new wall layer, like tile, shiplap or decorative stone, bring all device boxes out to the new wall surface with an electrical box extender.
Overfilling Electrical Boxes
Another fire hazard to avoid is stuffing as many wires as possible into an electrical box. Electricity produces heat, and keeping that heat to a minimum (thereby reducing the chance of fire) is why the NEC exists. That means overfilling boxes is a big no-no. You could be looking at melted insulation, ruined electrical devices, or worse.
The NEC limits the number of wires, devices, clamps and other accessories inside electrical boxes. This code requirement is called “box fill,” and it’s based on volume. Each item is assigned a value based on the gauge of the wire inside the box, and when added together, they must be less than the box’s volume.
Because the NEC occasionally updates box fill requirements, check with your local code authority to know which ones to follow. It’s also perfectly acceptable to buy bigger boxes than you technically need. Future electricians will thank you.
Installing Ceiling Fan In the Wrong Box
Before I was an electrician, I had a comically bad experience attempting to install a ceiling fan. My main problem was the old knob-and-tube wiring, but another roadblock was the ancient electrical box in the ceiling, which was not designed for the weight. Ceiling fans are heavy and rotate, often right over your family while they eat and sleep. They need to be properly supported.
If your fan is 35 pounds or more, it must be supported by a listed box that is marked with the weight the box can support. If the box is not marked, the ceiling fan must be independently supported by a ceiling joist or other structural member. If your fan is over 70 pounds, it must be supported independently no matter what.
Not Using Cable Connectors
Heat is not the only thing that can adversely affect an electrical installation; friction is another one. The wires running through your walls, usually contained in a cable called Romex, have a covering over them to reduce heat and to protect them from nicks and cuts that could cause electrical arcs.
I can’t tell you how many times I’ve opened up a box to find Romex resting, or even pulled taut, against the sharp edges of a metal electrical box. Over time, this friction point can wear down the insulation, so it’s important to use a cable clamp. Even plastic boxes common in residential use can be a hazard, though often these have an integrated clamp.
Replacing Two-Prong Receptacles with Three-Prong
Have you ever leaned down to plug in a three-prong appliance cord only to find that the receptacle only has two slots? Two-prong receptacles have a hot and a neutral, but no ground wire (more properly called an “equipment grounding conductor”). Today’s safety standards require a ground path back to the electrical panel, but if your house is old, you may still have two-slot receptacles with no ground path.
To bring these installations up to code, an electrician could rewire your house, pulling a ground to every receptacle. If that’s not in the financial cards, swap out the two-slot receptacles for GFCIs, labeling the front covers with “No Equipment Ground.” (Every GFCI comes with stickers for just this reason.) Or, add a GFCI breaker or a GFCI in the first outlet to protect the others downstream, swapping out the two-prongs for three-prongs. Label downstream receptacles with “No Equipment Ground” and “GFCI Protected” stickers.
Never swap out a two-prong for a regular three-prong, use an adapter, or break off the grounding prong on the cord (yeah, that happens). If you’re adding GFCI, update the AFCI protection, too, by using combination AFCI/GFCI breakers or receptacles where appropriate.
Upsizing Breaker Without Updating Wire
A breaker that constantly trips is trying to tell you something. You’re putting too much load on the circuit, or the wiring has a problem. Whatever the cause, you may be tempted to swap out the breaker for a bigger one to stop the tripping. Don’t. First of all, upsizing the breaker doesn’t diagnose what’s going wrong with your wiring. Second, the wires are now too small for the breaker. This is a recipe for an electrical fire.
Properly sized wires and breakers are one of the most important concepts in electrical work, so hire a licensed electrician for matters concerning your electrical panel unless you really know what you’re doing.
Backstabbing Instead of Using Screw Terminals
Unlike sizing breakers and wire, some projects are extremely DIY-friendly, like swapping out a receptacle. But even on a straightforward project like this, there are some tricks of the trade you should know. First up: Use the screw terminals on switches and receptacles, not the push-in holes.
Wires that are “backstabbed,” or pushed into the back of the device, tend to loosen over time. This can cause arcs, melted devices and fires. Instead, make a hook in the end of the wire and wrap it clockwise around the terminal screw. Tighten it with a screwdriver and tug on it to ensure it’s secure. Then, wrap electrical tape around the device, covering the screw terminals.
Reversing Hot and Neutral
When you flip on a lamp, electricity flows to the light on the hot wire and back to the panel (and transformer) on the neutral. This loop, or circuit, continues until you shut it off. But what if you accidentally swapped the hot and neutral? Would your light still work? Yes, but it would be a lot less safe. Here’s why:
If you look inside your lamp, the silver threaded receiver that holds the bulb is the “neutral”, and the “hot” is the small flap tucked down inside that touches the end of the bulb. Reversing hot and neutral to the light socket completes the circuit, but now the hot is on the silver threads instead of buried under the bulb. That’s going to shock someone eventually.
In newer house wiring, the hot tends to be black or red and the white wire is the neutral. When you have screw terminals, like on a receptacle, the hot goes on the brass screw, the neutral on the silver. For wires that aren’t clearly marked by color, like on a lamp cord, the hot is the smooth wire, and the neutral has ribs, grooves or other markings.
Not Calling a Licensed Electrician
Don’t mess around with your safety. Have a licensed electrician investigate frequently tripping breakers, buzzing devices, flickering lights, burning smells, scorch marks or melted devices. Always turn off the power (and verify it’s off) before looking into anything yourself.
Originally Published: August 23, 2018
