How to tell line and load wires when installing GFCI, dimmer/smart switch, or floor heating control

Do you get confused when installing a GFCI outlet, dimmer or smart switch, or floor heating controller and the instructions ask you to identify the line and load wires? You are not alone. These terms can be confusing. In this video I’ll explain an easy way to remember what these terms mean and how to use that knowledge when wiring these common devices a homeowner might use to upgrade their home.

0:00 Introduction
0:24 Line & Load
0:45 Light switch
1:25 Heating controller
2:20 GFCI plug
3:38 Summary

The information provided in this video is for informational purposes only. Usage of any information in this video is done at your own risk and the host and producer accept no liability. You should consult the local building code and requirements in your area and abide by all regulations when taking on any project in your home. Consult a licensed professional if you feel uncomfortable with any of the information in this video.

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[robertt]

Good to review the basic terms now and then. thank you for this easy to understand video. I am not an electrician but like most homeowners try to save some money now and then doing things myself. I am sure Tradesmen don't like it when info like this is posted.

[lmc]

This is very well explained, i finally understood it now after decades of being confused.

[kimjongoof]

I have 2 red wires and 2 black wires on my heating box. My relay + transformer wants me to connect L2 to its blue wire, L1 to its black wire, and load to its red wire. How do I tell which wire is the L1, L2, and load wire on my box?

[mnoble]

Very helpful! Thank you. I just want to make sure I understand fully. When installing a smart switch (which I plan on doing this weekend), red wires should be connected with black wires, white wires should be connected together, and the grounds should be connected together. My switch is a single pole, so I can skip the yellow wire. Is this correct?

[chadrowland]

I have a question. I have a central vacuum with direct connect wall valves with 120 volt power. How do I GFCI protect my central vacuum wall valve? And, should I put a label making them as GFCI protected outlets?

[ianbelletti]

I've learned to equate line with the power lines and load with the equipment side of the circuit. Put simply, its the line side because if you follow it from the device location the wires will lead you toward the panel and the power lines coming in. Load will always lead you toward devices and equipment that utilize the power.

[shannagarroutte]

In a situation with four wires, I can figure out which black wire is hot, but how do I know which white wire goes with that black hot wire (to create a line “pair”) and how do I know which white wire is the load wire

[wellsnapyeah]

That’s a great way to remember lINe and lOad

[jackriley]

All of this in case the Chinese manufacturer forgot to include installation instructions??

[georgedavall]

Don't let loser comments discourage You!

[RR-hmqj]

What if both wires are black and smooth and the old device isn't marked and both screws are brass? And you don't have a tester? 😂

[TrevorSachko]

If you are that easily confused you had best leave it to a tradesman...