Line vs. Load Wiring: What's the Difference?

In the electrical trades, the terms "line" and "load" are shorthand words that refer to the electrical wires that deliver power from the source to a device (line), vs. those that carry power onward to other devices further along the circuit (load). A number of other more conversational terms are also used to describe the same thing, such as incoming vs. outgoing wires or upstream vs. downstream.

What Is a Line Wire?

The two terms are used in the context of a single device and electrical box. So, the wires that deliver power into the box are described as the line wires, also known as upstream wires, or the incoming wires.

What Is a Load Wire?

Conversely, the wires passing onward to other devices are described as load, downstream, or outgoing wires. These terms are relative to the location of the device in the circuit, since the load wire for one outlet becomes the line wire for the next receptacle downstream in the circuit.

The terms "line" and "load" have a number of applications at different locations in an electrical system.

What Is the Difference Between Line and Load Wiring?

The incoming feed from the utility company comes into the line side of an electric meter. It leaves the meter from the load side and then feeds the line side of a disconnect or electrical service panel. The service panel also has line and load connections—the line feeds the main breaker in the panel, while the individual branch circuit breakers can be considered the load, with respect to the main breaker.

How to Differentiate the Line vs. the Load Wire

Wire Position

Line wires are usually found lower than load wires, as the line wires are delivering power. Load wires tend to be positioned near the top of outlets and switches.

Wire Color

Line wires are usually are black, and load wires are usually white. However, this is not always the case. Consider multiple factors and not just color when identifying which wire is which.

Testing the Wire

There are also a couple of devices you can use to test which wire is which, including a multimeter, and a non-contact voltage tester. If you aren't satisfied with your findings with only position and color in mind, consider one of these options as well.

When Do You Need to Determine Line Wire From Load Wire?

Circuits

Outlets (receptacles), switches, light fixtures, and other electrical devices typically are wired in multiples on a single circuit. With the first device, the line is the wire running from the service panel to the device, and the load is the wire running from the first device to the second device downstream on the circuit. At the second device, the line is the power source coming in from the first device; the load is the wire going out to the third device on the circuit, and so on.

The same meaning can apply to the device itself. The line side of an outlet is where you connect the incoming source power. The load side is where the power leaves the device (or electrical box) and travels down the circuit.

GFCI Outlets

Line and load have special meaning when wiring ground-fault circuit-interrupter (GFCI) outlets. GFCIs have two pairs of screw terminals for connecting wires: One pair is marked LINE, and one is marked LOAD. Connecting to the line terminals only results in the outlet providing GFCI protection only for that outlet. Connecting for the line and the load terminals (using two electrical cables or two sets of pigtail wires) provides GFCI protection for that outlet as well as for other standard outlets located downstream on the same circuit.

Other Meanings of "Line" and "Load"

When wiring low-voltage circuits, such as those supplying doorbells or landscape lights, "line" refers to the parts of the circuit that are at full household voltage (usually 120 volts), to distinguish them from the low-voltage wiring and devices that are used after the voltage is stepped down at a transformer.

"Load" is also a general term to describe the electrical demand, or power draw, that a device or appliance places on a circuit. For example, on a lighting circuit, you can add up the maximum wattage of all of the light fixtures on the circuit to calculate the "total load," or maximum potential power demand of all the lights.