Electrical wiring can be easy enough for the average homeowner, but there are some common mistakes that happen far too often. These may seem innocent enough at the time, or they may go completely unnoticed, but their consequences can be severe: A simple pinched wire or loose connection can lead to a fire that burns your house down. So work carefully and always follow the local electrical code rules. If you make a mistake or damage some wiring in any way, stop and fix the problem before finishing... the rest of the project. Common electrical mistakes are disasters waiting to happen.
01 of 09
Improperly Installed Wire Staples
When installing NM (Romex) electrical cable, you typically must secure it to the wall, ceiling, or floor framing with cable staples. These are easy to install but just as easy to get wrong. Amateur electricians commonly hammer the staples too tightly, which can pinch the wires inside the cable, possibly damaging the insulation or creating a point of electrical resistance, which can make the wires hot.
A pinched wire is particularly dangerous because if the metal staple cuts through the... insulation, it can lead to an arc fault, a very common cause of electrical fires.
02 of 09
Box Installation Mistakes
Nailing an electrical box to wall or ceiling framing seems simple enough, but often they are installed too deep for the drywall or other finish material. If you’re installing 1/2-inch drywall on a wall in a living room, for example, the face of the box should extend 1/2 inch out from the face of the wall stud. This ensures that the face of the box will be flush with the drywall when it is installed.
If a box is mounted too deeply and there is more than 1/4 inch between the box's front edges... and the face of the wall finish, install a box extension ring to bring the box flush with the wall surface.
03 of 09
Improper Wire Sizing
Electrical wiring size relates to how much amperage (amps), or electrical current, it can safely handle. For example, 14 AWG (gauge) wire is rated for a maximum of 15 amps; 12 AWG is rated for 20 amps. If you're tapping into a circuit that has a 20-amp breaker, you must use 12 AWG electrical cable. If you use 14 AWG wiring on that circuit, the wiring won't be adequately protected by the 20-amp circuit breaker, and the wires could overheat and cause a fire without the circuit breaker... tripping.
04 of 09
Over-Fusing a Circuit
Over-fusing is a common mistake that happens in older houses with fuse boxes (rather than breaker boxes). With older-style fuses, the screw-in fuses all have the same size of base, and it's possible to replace a 15-amp fuse with a 20-amp fuse, even though the circuit wiring is rated for a maximum of only 15 amps. If there's a problem in the circuit, such as a short or arc fault, the fuse may not blow before the wiring overheats, which can cause a fire.
All fuse boxes today should use Type... S, or "tamper-proof," fuses that have a specific base size for each amperage rating, preventing over-fusing.Continue to 5 of 9 below.
05 of 09
High-Wattage Light Bulbs
Everyone has been guilty of this at one time or another. Most light fixture in a home have a maximum rating for light bulb wattage, and 60-watt is the most common. The maximum wattage is usually posted next to the socket for safety purposes. If you ignore the notice and use a bulb with higher wattage than the maximum rating—for example, using a 100-watt bulb in a 60-watt fixture—the bulb can melt the wiring insulation in the fixture, creating a potential shock and fire hazards.
The solution is... simple: Don't exceed the wattage maximum or, better yet, use LED bulbs instead of incandescent. LEDs have much lower wattage ratings (by a factor of seven) with the same amount of light output.
06 of 09
Short Wires in a Box
When making a connection in a junction box, the length of wire in a box is important. The general rule of thumb is to install 6 inches of wire in a box in order to have enough to make proper connections. You need enough wire to strip and connect the wires to use the wires in the future, if necessary. Once connected wires are folded neatly into the box.
On the other hand, having too much wire in a box can be just as bad as too little. In this case, when you try to jam too much wire in the box and... also install devices in the same box, there is always the chance that the wires could get damaged and short out.
07 of 09
Loose Wire Connections
Connections of wires should be made with wire connectors. Wires should not simply be twisted together and wrapped with electrical tape, as this connection can easily come loose.
Loose connections on switches and outlets pose another problem. When tightening a wire around a terminal screw on a device, bend the stripped wire into a semicircular loop and put the open end of the loop towards the right. Tighten the screw in a clockwise motion until tight. This will draw the bare metal end of the wire... around the screw, thus closing the loop tighter. If you have the open end the other way, the loop will actually open up a bit, causing the connection to not be as secure.
08 of 09
Connecting Wires to the Wrong Terminals
Connecting a wire to the wrong terminal on an outlet, appliance, or other electrical device can cause several potential problems and can be very dangerous.
When wiring an outlet, for example, the hot wire of a circuit connects to the brass-colored screw terminal; this is connected to the short straight slot on the face of the outlet. The neutral wire connects to the silver-colored terminal, which connects to the longer straight slot of the outlet.
The ground wire is simple. It connects to the... green screw on the outlet, which cannot be mistaken for the other two. The ground connection is made through the D-shaped slot on the outlet.Continue to 9 of 9 below.
09 of 09
Whether it's too many holiday lights or a pile of wires for the entertainment center. You get one of those handy multi-outlet power strips and plug in every cord you can fit into the strip. But the strip plugs into one outlet, which is on single circuit that can only handle only 15 amps, and you're trying to pull 18 amps from it. If you're lucky, the breaker keeps tripping until you get the message. If not, you can overheat the circuit wiring and potentially cause a house fire.