a gfci replacement plug being wired and installed

Line vs Load

Originally contributed by Jeff Butler • last updated 1/12/2021

If you’re thinking about changing out an older electrical outlet with a newer GFCI replacement plug, you’re probably going to need to be familiar with a few electrical terms. Two terms in particular that can often cause confusion are line vs load wires.


When talking about your home’s electrical system, the terms line and load are often used to refer to a couple of the wires that are needed to connect an outlet or light switch to your home’s power source. The line wire (sometimes referred to as the incoming wire or upstream wire) delivers power to the outlet or switch and the load wire (also known as the outgoing wire or downstream wire) either carries it along to the next connection or to a device, such as a garbage disposal or a microwave, that’s in need of power.

Line vs Load — How Can You Tell The Difference?

Identifying and connecting your line and load wires properly when installing a new GFCI outlet or a new light switch is important to ensure it operates correctly. Here are a few tips to help you get it right and avoid mistakes:

  • Sometimes, you can identify the line and load wires by the color of their sheath. Line wires are typically black and load wires are often red. However, this may not always be the case and both wires may be black (or even a different color).
  • If you’re still unsure, you can use a voltmeter or a multimeter to identify the line and load wires. However, it might be best to call a professional to help as working with electricity can be very dangerous.