How To Tell Line From Load Wire

In some cases line wires are marked with line pwr or a lightning bolt symbol.

How to tell line from load wire. The load wire is usually coming from the top of the box. Connect it to the line side of your gfci. Before removing the switch test each wire with a voltage tester. For most other purposes you don t need to know.

A line and a load wire may be in the same junction box depending on where the line source conductor comes in and where it is going next but the schematic for making a multiple 3 way and 4 ways work is always the same. For example a conventional wall switch which is a single pole single throw switch works equally well whether you attach the live circuit wire line to the top brass terminal or the bottom because the switch has only two positions open or closed the terminal connections are directional on a double throw switch on the. If line and load are both black. The white wire is the neutral wire which takes any unused electricity and current and sends them back to the breaker panel.

If the wire is coming from the top of the switch box it is likely your load wire. The load wire will not be hot and will have no voltage on it until it is connected with the line wire. It s upstream of the switched device s. Line is always hot.

The rest are your. Line is the wire going from a current source into a switch. Determining which is which can be tedious. 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.

So pick one black white pair at random. My typical methodology for this has been to turn off the breaker disconnect a nm wire put caps on the wires that i disconnected put the outlet back in place and flip the breaker back on. Identify wires by color. Distinguishing between line and load isn t always necessary.

Once you do this follow it back to where you see the outer sheeting covering all three wires white black and bare copper ground in that romex wire and this is your power supply in. I might assume that since you are trying to figure out line vs. The line wire is usually coming from the bottom of the box. Load wire generally connected to the top half of your switch.

Turn the breaker back on. I really don t like using. Load is the wire going from the switch to the device. An easy way to identify the wires in your wall box is by looking at the color.

Load will only be hot if the switch is closed. Leave the other black white pair unconnected but isolated. Load you might be installing a gfci receptacle. To determine the line vs load wires you need to take note of how everything is connected and write it down then disconnect the wires and use a volt meter to see which black wires have power.

Unlike conventional outlets gfci outlets care about which wires are line where power feeds from and load outlets that get power from the gfci.