In terms of electrical trades, the terms line and load are shorthand words. One refers to wires which deliver power from the source to a device. Whereas, the other refers to those wires which carry the power onto other devices along the circuit.
There are many more conversational terms that can be used to describe such wires. For instance, they’re also called incoming and outgoing wires or upstream and downstream wires. The terms line and load have many applications at different locations in an electrical system.
However, if you’re not a mechanical expert, it’s really easy to mix them up. But don’t worry, as I’ve got you covered! In this article, I’ll be providing a range of differentiating factors that can help distinguish these two wires apart.
So let’s get right to it!
What’s the Difference Between Load and Line Wires?
The difference between them is pretty straightforward. The line wire is the one that goes from a current source into a switch or an outlet device. Whereas, the load wires is the one that goes from the switch to the device or appliance.
Outlets, switches, light fixtures, and other electrical appliances are wired on a single circuit in multiples. The line wire runs from the service panel to the first device.
On the other hand, the load wire runs from the first device to the second device “downstream” on the circuit. The line wire is “upstream” from the switch in terms of the flow of electricity. Another meaning for load refers to the magnitude of the energy consumed by devices on a circuit.
For the second device, the line is the power source coming in from the first device. Whereas, the load wire is flowing out to the third device on the circuit and so on.
Differentiating between a line and a load wire isn’t always necessary. For instance, a conventional wall switch has a single-pole, single-throw switch.
It’ll work equally good if you attach the live circuit wire, which is line wire, to the top brass terminal or if you attach it to the bottom. This is because the switch only has two positions. It’s either open or closed.
However, on a double-throw switch, the terminal connections are directional. This is because it can transfer power between multiple loads.
In such a switch, the line and load terminals are clearly marked. The live circuit wire must always be connected to the line terminal in this case.
There’s also a difference between line and load wires in terms of the GFCI outlet. A GFCI outlet is short for “ground fault circuit interrupter”.
These have two pairs of screw terminals for connecting wires. One pair is clearly marked with a line and the other is marked as a load.
If you connect only to the line terminals, the outlet will be providing GFCI protection only for that specific outlet. Whereas, if you connect to both line and load terminals, then GFCI protection will be for other standard outlets as well. These are located downstream of the circuit.
How Can You Tell if a Wire is a Load or Line?
Now that you know the meanings of line and load wires, let’s take a look at a few factors which will help tell them apart.
Line wires supply electricity from the main power lines to electrical switches. These power lines get electricity from the utility power companies and then send it to a house. They’re also known as incoming wires or upstream wires.
Their main purpose is to supply electricity to the house or building. Sometimes it gets really challenging to differentiate between line and load wire colors. This is because different countries denote different colors to each of the wires.
So then how would you identify line and load wires? There are many ways of identifying these wires in your own house. Here’s a list of a few ways in which you can do that:
- Determine the position of the wires.
Line wires are always connected to the electrical panel from the bottom. Whereas, load wires are always connected from the top. So by simply looking at the position of the connected wires on the circuit, you’ll be able to differentiate between the two wires in the panel. - Test each wire using a voltage tester.
You can use a volt stick or a pen which will help detect the voltage without you touching the bare copper wire. Make sure that you test each wire which is connected to the switch using this pen. When the pen tester glows red, this means that the wire is a line wire. However, if the pen tester doesn’t glow at all, then that is a load wire. A volt stick is an efficient device to use when testing wires. - Use a digital multimeter for testing.
Basically, a multimeter is an electrical device that measures the electric values, voltages, resistance, and current in an electrical panel. Switch on the device knob to AC voltage to read 200 volts. Then hold the insulated terminals of the multimeter and test the terminals of wires connecting to the switch. If the reading comes out to be 120 volts, or above, then those are the line and load wires. - Use a neon screwdriver.
This screwdriver is a tool that has a neon light inside the transparent plastic handle and a metallic tip. You can use this to touch the bare wire or the screws connecting the wire to the meter box. The neon glows if you’re touching the line wire. This means that the current is flowing in that wire. However, when touching a wire which has no current flowing, then the neon light doesn’t glow.
The above ways are quite easy as well as reliable. You can use either way to help differentiate between a load wire and a line wire in an electrical circuit.
What Happens if I Mix Up Line and Load wire?
If the load or line wires get mixed up, then the GFCI protection will no longer be there. This means a ground fault won’t trip the GFCI. While there will be an appearance of protection, there’s no actual protection.
The GFCI outlet contains a breaker that interrupts the current when it detects a sudden current surge. If you interchange the line and load wires on a conventional outlet, it’ll have no such effect on the outlet.
However, if you interchange them on a GFCI outlet, then that’ll cause the breaker to be ineffective. This could be potentially very dangerous because the outlet then won’t be able to provide the protection that it’s designed to give. It’ll be exposed!
The load wires from one upstream in the circuit must always be connected to the line terminals of the one downstream. Otherwise, the downstream one won’t function properly.
Therefore, it’s really important to know the difference between load and line wires. You may also seek help from professionals in this field if you can’t understand it yourself.
Is Hot Wire a Load or a Line?
Typically, the line wire is the hot wire. It goes from a source to a switch and it’s upstream of the switched device. Hotwires are used as initial power feeders to a circuit.
These carry currents from the power source to the outlet. As they’re the first instance of a circuit, they’re always carrying electricity which is why they’re hot. It’s dangerous to touch a hot wire when it’s connected to a power supply.
Basically, line wires comprise three wires. These are hot, neutral, and ground wires. The ground ones are bare, whereas, the hot and neutral ones are both insulated.
When the hot wire has taken the power from a source, there’s another wire to complete the circuit. This is the neutral wire which carries the circuit back to the original power source. They bring the circuit to a ground usually connected to the electrical panel.
Hotwire can be identified by its black casing. This is the main color of the hot wire in most homes.
However, they can also be red, blue, or yellow. These colors can indicate a different function besides that of powering an outlet.
Like hot wires, most electric wires are insulated to protect users from shocks. Each color on these electric wires has a different meaning. Although, the colors can be used interchangeably depending on different countries.
Use this table listing the range of colors and the wires that they represent as a guide:
| Wires | Insulation Colors |
| Neutral Wire | White and Grey |
| Ground Wires | Green with yellow stripes or green and copper |
| Line/Upstream Wire | Black casing |
| Load/Downstream Wire | Red or black casing |
Do All Light Switches Have a Load Wire?
A switch always has to have a load wire. Otherwise, it wouldn’t be able to turn anything on and off.
However, people often get confused between wires when dealing with a three-way switch. In such switches, the white wire is used to carry the current.
Therefore, it can be understood that white wires don’t always mean neutral wires. Sometimes they can also be load wires.
Moreover, the standard single-pole light switch will require you to attach the load wire to it. Then the other wire which is leaving the switch to your lights.
So basically, a load wire in a light switch is the one that connects your switch to your light bulb or other types of load. Usually, the load wire’s color is black. However, in some countries or in a three-way switch it can also be white.
Load is also a general term that is used to describe the electrical demand or power draw a device puts on an electrical circuit.
Take a quick look at this video explaining how single pole switches work:
Final Thoughts
To summarize, the main difference between a line wire and a load wire is that the former carries power from the current source to a switch. Whereas, the latter carries this power from the switch to a device or an appliance.
The line wire is always the hot wire and it’s upstream of the switched devices. On the other hand, a load wire is downstream on a circuit. A load wire will only be hot if the switch is closed.
There are many ways you can use to identify the load and line wires in an electrical panel. These include using a neon screwdriver, a digital multimeter, or simply checking the positions of the wired on the meter box.
Each wire has insulation that has different colors. These colors vary from country to country. The line wire is usually always the black wire. I hope this article helped clarify the difference between the two electrical wires!
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