7 Common electrical wiring mistakes | Pro Construction Guide
Avoid these electrical wiring mistakes

Avoid these 7 common electrical wiring mistakes

If you encounter one or more of these common electrical wiring mistakes while working on a job, get it corrected before you proceed with the work. Electrical wiring mistakes should not be taken lightly; they can result in short circuits, injury and fire.

Some of the “fixes” for these electrical wiring mistakes are easy to do, but if you decide to correct the problem, you will held responsible for the wiring you do. Any electrical work you do must conform to the National Electrical Code (NEC), or NFPA 70, a standard for the safe installation of electrical wiring and equipment in the United States, as well as to state and local codes.

If you’re not sure how to fix the problem, get a qualified electrician. ALWAYS turn off the breaker switch before working on any electrical circuit.

Electrical wiring mistakes: Connections without electrical boxes

Mistake 1: Connections without electrical boxes

Mistake 1: Connections without electrical boxes

The picture shows a light connected without an electrical box. This is extremely dangerous as any sparks or heat will be uncontained, a definite fire hazard. Disconnect the fixture, install an electrical box and then reconnect the fixture.


Electrical wiring mistakes: Wires cut too short

Mistake 2: Wires cut too short

Mistake 2: Wires cut too short

Wire that has been cut too short is extremely difficult to work with. Wire should extend about 3 inches from the box. By adding connecters, it is possible to extend the wire. Make sure your connector screws are tight.


Electrical wiring mistakes: Leaving plastic-sheathed cable unprotected

Mistake 3: Leaving plastic-sheathed cable unprotected

Mistake 3: Leaving plastic-sheathed cable unprotected

Plastic-sheathed cable is easy to damage. All cable must be protected, particularly in vulnerable areas. The cable in the picture is not sheathed to code. Plus, in this case, someone has bundled the cable with bailing wire. This is a disaster in the making. At the very least, replace the wire with zip ties. Ideally, the cable should be replaced.


Electrical wiring mistakes: Recessing boxes behind the wall surface

Mistake 4: Recessing boxes behind the wall surface

Mistake 4: Recessing boxes behind the wall surface

This outlet was installed during a bathroom remodel. In order to install the electric box, the contactor cut the upper part of the box away, this has left flammable material exposed to the danger of heat and sparking. This box should be replaced with an intact box. Because it’s in a bathroom, it needs a GFCI outlet to meet code.


Electrical wiring mistakes: Overfilling electrical boxes

Mistake 5: Overfilling electrical boxes

Mistake 5: Overfilling electrical wiring boxes

NEC specifies the size box for the number of wires. In this picture, the number of wires exceeds the capacity of the box. Overheating, shorting and fire are very real dangers. Remove the box and replace it with a larger box that meets code.


Mistake 6: Reversing hot and neutral wires

Today outlets are color coded. Brass is for the hot or black wire and silver is for the neutral or white wire. If you connect the hot wire to the silver connection, the appliance or fixture will still work but it can produce an electric shock. If you find an outlet that is improperly connected, reverse the wires.

Electrical wiring mistakes: Mix the line and load connections

Mistake7: Mix the line and load connections

Mistake 7: Wiring a GFCI backward

One of the most common electrical wiring mistakes when wiring GFCI, is to mix the line and load connections. The outlet will work but won’t trip if there is a ground fault. Here’s how to install it correctly,

A GFCI (ground fault circuit interrupter) has two terminals. One set for the line that has incoming power. One set for the load that carries power to other outlets. NEC requires these circuits for bathrooms, kitchens, basements, and all outside outlets, including the garage.

If you are not sure which wire is the line and which is the load, here’s how to find out.

  • Turn off the breaker switch. (Tape a note to the breaker box letting people know it is being worked on if other workmen are on the project.)
  •  Take the outlet from the box without detaching the wires.
  •  Disconnect a black and a white wire. Check to see they are from the same cable. Separately cap them off.
  •  Reattach the outlet and faceplate. Turn the breaker switch on.
  •  Plug an appliance into the outlet. If the appliance works, your capped wires are load wires. If it doesn’t work, you have capped the line wires.

Now that you know which wire is which, turn off the breaker and reopen the circuit. The live or black wire is always connected to the brass terminal, and the neutral or white wire is always connected to the silver terminal. Be sure you are connecting the line to the line and the load to the load following the color coding.

Connect the ground wires (green) together with a short third piece of ground wire and use a wire nut to make the connection. The third piece of wire will form a tail. Connect the tail to the green GFCI terminal.

On metal electrical boxes, attach a ground wire from the wire nut to the electrical box ground screw.

Finally use a GFCI circuit tester to test the circuit. Or if you don’t have one, you can:

  • Turn the breaker on
  • Fully press the reset button on the GFCI
  •  Plug in an electrical appliance and leave it on to make sure everything is working
  •  Press the test button and the outlet should trip
  •  Press the reset button and the power should turn on

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