Repairing electrical wiring, more than any other household project is all about safety. Install an outlet properly and it's as safe as it can be; install it improperly and it's potentially deadly. That's why there are so many rules surrounding electrical wiring and installations. The rules can be complicated, for sure, and sometimes confusing, even for master electricians, but there are basic concepts and practices that apply to almost every electrical wiring project, especially the kind that DIYers are qualified to tackle.
01 of 05
Test for Power
The best way to prevent electrical shock is to ALWAYS test wires and devices for power before working on them or near them. Simply shutting off the power isn't good enough.
A Cautionary Tale
Intending to replace a light fixture, you shut off the power to the fixture's circuit at the circuit breaker. You remove the fixture, exposing the electrical box, where you find a slightly complicated wiring situation—inside the box, there are four electrical cables. Two belong to the fixture circuit, while the other two belong to another circuit. The installing electrician used the box as a junction box for another circuit (for which you didn't shut off the power). You assume they're all part of the same circuit, but in reality, you're digging around in a box with live wires.
If you tested for power inside the box—this takes just seconds with a non-contact voltage tester—you would know that those two cables still have power and that you have to find their circuit breaker and shut it off.
Mislabeled Circuit Breakers
Further, it's not uncommon for circuit breaker boxes to be mislabeled, especially if the electrical service has been extended or adapted over the years. The circuit breaker label may not accurately describe what the circuit breaker actually controls.
Always test for power before working on any circuit wires.
02 of 05
Check Amperage Ratings
All electrical wiring and devices have an amperage, or amp, rating. This is the maximum amount of electrical current they can safely carry. Most standard household circuits are rated for 15 amps or 20 amps, while large-appliance circuits (such as for electric dryers and ranges) may be rated for 30, 40, 50 amps, or even more.
When installing or replacing wiring or devices, all of the parts you use must have the appropriate amperage rating for the circuit. For example, a 20-amp circuit must have 12-gauge wiring, which is rated for 20 amps. If you install 14-gauge, 15-amp wiring on that circuit, you create a fire hazard because the 20-amp circuit breaker protecting that circuit might not shut off before the 15-amp wiring overheats.
Choosing the Right Amperage
When replacing a switch, light fixture, or outlet receptacle, make sure not to install a device that is rated for more amperage than the circuit carries. This is especially important when replacing receptacles. A receptacle rated for 20-amps has a unique prong shape in which one of the vertical slots has a T shape. This shape allows 20-amp appliances, which have a matching T-shaped prong, to be inserted. Installing such a receptacle on a 15-amp circuit makes it possible to possibly overload the circuit if you plug such a 20-amp appliance into it.
Note, however, that there is no danger to installing 15-amp receptacles in 20-amp circuits since it is perfectly fine when a plug-in device draws less power than the circuit amperage. In fact, it is quite normal for 20-amp general-use circuits to be wired with 15-amp receptacles.
03 of 05
Make Tight Wiring Connections
Electricity travels along conductors, such as wires and the metal contacts of outlets and sockets. Tight connections between conductors create smooth transitions from one conductor to another. But loose connections act like speed bumps, restricting the flow and creating friction and heat. Very loose connections can lead to arcing, in which electricity jumps through the air from one conductor to another, creating tremendous heat.
Prevent fire hazards by making sure all wiring connections are tight and have full contact of the conductors being joined. When splicing wires together, always use approved wire connectors ("wire nuts").
Outlet receptacles and switches are often manufactured with push-fit wire connection slots on the back, along with the traditional screw-terminal connections on the sides of the device. These push-fit connections are notorious for loosening or failing, so professional electricians almost unanimously avoid them in favor of making very tight and secure screw terminal connections.
04 of 05
Respect Grounding and Polarization
Grounding and polarization are essential for the safety of modern electrical systems. Grounding provides a safe path for stray electrical current caused by a fault or other problem in a circuit. Polarization ensures that electrical current travels from the source along "hot" wires and returns to the source along neutral wires.
Always follow manufacturer's wiring diagrams when replacing a fixture, and understand—and use—your home's grounding system to ensure grounding and polarization remain intact.
There are a variety of ways to test for grounding and polarization. A simple plug-in circuit analyzer tool, available for a few dollars, will make it possible to routinely check outlets to make sure they are wired correctly.Continue to 5 of 5 below.
05 of 05
Box and Clamp It
The National Electrical Code (NEC) requires that all wiring connections be made in an appropriate enclosure. In most cases, this means an electrical box. Enclosures not only protect the connections—and protect people from accidental contact with those connections—they also provide means for securing conductors (like electrical cables) and devices.
The rule here is simple: don't be lazy. If you need to make a wiring splice, install a junction box and secure the cables to the box with cable clamps. Never leave a splice or other connection exposed or unsecured.