a gfci replacement plug being wired and installed

Line vs Load

Originally contributed by • last updated 3/16/2021

Home Depot
Home Depot

Making improvements or changes to your home’s electrical system is probably not something you want to get into unless you’re familiar with the basics of electricity. For example, 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 couple of electrical terms, specifically the terms line and load. These two terms in particular often cause confusion and can cause even more problems if they’re not hooked up correctly.


When talking about your home’s electrical system, the terms line and load are often used to refer to two of the wires that are needed to connect an outlet or light switch to your home’s power source. The line wire, which is sometimes referred to as the incoming wire or upstream wire, delivers power to the outlet or switch. Whereas, the load wire, which is also known as the outgoing wire or downstream wire, either carries power along to the next connection or device, such as a garbage disposal or a microwave, or it returns it back to the source. Confusion around these two wires and their terms has led to the common expression, line vs load.

What’s The Best Way To Determine Line vs Load Wires?

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. Mixing up the wires can not only prevent the outlet or switch from working properly, it can also cause serious damage to your home’s electrical system. 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 sheaths. 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.
  • Warning: Accessing your home’s electrical system can have serious consequences if not done properly. Please, consult a professional before attempting any repairs or maintenance.