Making Connections Outside Electrical Boxes

Mistake: Not using an electrical box.

"Electrical boxes, sometimes referred to as junction boxes, protect connections from accidental damage, and help contain sparks and heat from a loose connection or short circuit," says Gerald Talbot, licensed electrician with Mister Sparky. "Failing to make connections inside the electrical box is arguably the biggest mistake a homeowner can make, as this can result in major hazards."

Solution: Add a box.

If you start a project and find a jumble of taped-together wires stuffed in the wall cavity instead of neatly contained in a junction box, don't ignore it. (This happened to me, with a century-old knob and tube wiring.) Ensure the power is off, add a box and reconnect the conductors. If you're not near a stud, use "old work" remodel boxes that grip right to the drywall.

Backstabbing Instead of Using Screw Terminals

Mistake: Backstabbing electrical connections

Receptacles and light switches have holes where you can insert the conductors instead of attaching them to the terminal screws. "Backstabbing" is technically acceptable (after all, the holes are right there), but the connections tend to loosen over time, potentially causing electrical arcs and fires.

Solution: Use the screw terminals.

Every electrician I've ever met (including me) prefers using the terminal screws, or pigtailing to them, instead of backstabbing. Make a hook on the end of the conductor and wrap clockwise around the terminal screw. Tighten with a screwdriver.

Reversing Hot and Neutral

Mistake: Reversing hot and neutral

This creates a shock hazard, and because the light or device will likely still work, you won't even know it until it's too late.

Solution: Identify wires and terminals

In a standard NM-B cable, the black wire is the hot, the white is the neutral and the bare copper wire is the equipment grounding conductor (EGC). When wiring receptacles and light switches, attach the black wire to the brass screw (labeled HOT), and the white wire to the silver screw (labeled WHITE). The bare ECG goes to the green ground screw.

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.

Installing Cable Without a Clamp

Mistake: Missing cable clamp

I can't tell you how often I've found NM-B (Romex) cable resting, or pulled taut, against the sharp edges of a metal electrical box. Over time, this friction point wears down the insulation and is a major fire hazard.

Solution: Use a cable clamp.

"When using metal junction boxes, it is important to use a cable clamp to ensure the cable is securely fastened within the box and conductors will not get exposed outside of the box," says Chris Lozano, master electrician and virtual electrical expert at Frontdoor. Make sure the clamp is secure around the cable, Lozano says, but don't crank down too much to avoid constricting the wires.

Using the Wrong Size Conductors

Mistake: Choosing the wrong wire size.

Electrical conductors' diameter, or gauge, determines how much current they can safely carry. Using too-small wires causes overheating, but unnecessarily large wires are a waste of money.

Solution: Match existing conductors.

When doing DIY electrical work, check the size of the breaker and match the existing wire in the box. Most of the time, you'll see 14-gauge conductors on 15-amp circuits, and 12-gauge wire on 20-amp circuits. It's okay to have bigger wires than necessary, but never go smaller.

Upsizing Breaker Without Updating Wire

Mistake: Swapping out a breaker without updating conductors

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. If you're tempted to swap out the breaker for a bigger one to stop the tripping, don't. Upsizing the breaker doesn't diagnose your wiring problem, and the old wires will be too small for the new breaker.

Solution: Call a licensed electrician.

Hire a licensed electrician for matters concerning your electrical panel unless you really know what you're doing.

Overloading Electrical Circuits

Mistake: Too many devices on one circuit

"An overloaded circuit can lead to device and wire failure, which can ultimately lead to fire and destruction of equipment," Lozano says.

Solution: Keep things separate

If you're roughing in a new addition or trying to decide whether a circuit can handle another appliance, err on the side of caution. "Things like window AC units, space heaters, microwaves, and other appliances can be a huge draw, so it is best to keep them separate or run dedicated circuits when possible," Lozano says.

A 15-amp circuit can handle 1800 watts, a 20 amp circuit 2400 watts. Look at the amps or watts listed on your appliances and devices, and add them up. (To convert amps to watts, multiply amps by 120 volts. To find amps from watts, divide watts by 120 volts.)