How to Identify Wiring

Service Panel

When you open an outlet, it can be useful to figure out the position of the outlet or switch in the circuit, as well as the function of each wire. This knowledge can help you pinpoint problems and connect wires to the correct terminals when making repairs.

If you can't find the source of a problem with an outlet, work from that point back to the service panel, troubleshooting each load on the circuit and its connections until you locate the fault.

End-of-Run Outlet

When there's only one cable entering an outlet box, it means the outlet is the last fixture on the circuit. Power comes from the service panel along the black (hot) wire through other outlets, switches, and light fixtures on the circuit and begins its return to the source through the white (neutral) wire attached to this outlet. The black wire attaches to a brass terminal; the white wire, to a silver terminal.

Middle-of-Run Outlet

Two cables entering an outlet box indicate that the outlet is not the last fixture on a circuit. One of the black wires receives power from the service panel; the other sends it on to other loads on the circuit. The white wires allow current passing through the outlet and the other loads on the circuit to return to the panel.

Electrical Wires

Here's a rundown of electrical wires:

• The black wire is the "hot" wire, which carries the electricity from the breaker panel into the switch or light source.
  
• The white wire is the "neutral" wire, which takes any unused electricity and current and sends them back to the breaker panel.
  
• The plain (or it can sometimes be green) wire is the "ground" wire, which will take electricity back to the breaker panel, then outside to a rod that's buried in the ground. This is to prevent the electricity from running through you!

Electrical Safety Rules

• Wear rubber-soled shoes.
  
• Avoid wet floors.
  
• Use nonmetallic ladders.
  
• Use tools with rubber grips.
  
• Check with your local electrical-codes department to make sure you're doing any do-it-yourself project properly.