How to identify the load line and wires

Do you want to install a new wall socket or switch in your home but don't know which wire is the line and which is the load?

Are you trying to determine if your line and load wires are wired correctly?

No one wants to be in danger of a fatal electric shock, and if you answered yes to this question, then you've come to the right place.

Our article presents the entire process of identifying line and load wires.

Let's get started.

What are line and load wires

"Line" and "Load" are terms used in electrical connections in which a device receives and sends current to other devices.

The line wire is the upstream wire from the main power supply that supplies power to the outlet.

It is always hot (always conductive) when there is power from the power supply. 

A load wire, on the other hand, is a downstream wire that diverts current from an outlet and supplies it to other electrical devices. It is only hot when the socket switch is turned on (indicating a closed circuit with current flowing through it).

There is usually a third wire, which is an unused ground connection that works specifically with line wire and protects against fatal electrical shock.

A poor line-to-load connection at a GFCI outlet in your home, for example, renders its circuit breaker useless and exposes you to a fatal electric shock hazard.

This is why you need to identify wires before making any connections.

Tools needed to define line and load wires

The tools you need to identify your line and load wires include:

• Multimeter
• Multimeter probes
• Non-contact voltage tester
• neon screwdriver

They help provide more accurate results.

How to identify the load line and wires

The line is usually a black insulated wire that goes to the bottom of the switch, and the load is a red wire that goes to the top of the switch. Alternatively, you can use a voltage tester or multimeter to check the voltage reading on one of the wires.. 

These identification methods, as well as other ways you can identify line and load wires, are broader. We'll take care of them now.

Identification of line and load wires by color

The easiest way to distinguish a line wire from a load wire is to use color coding. 

As a rule, the wires are insulated with rubber to protect us from the danger of electric shock. This rubber insulation also comes in different colors and has a special meaning to them.

When it comes to line and load wires, black rubber is commonly used for the line and red rubber for the load. If you have wires in this color code, your problem is solved.

However, there is still a problem. Since wire color has nothing to do with whether they work or not, color codes can be interchanged.

For example, red rubber can alternatively be used for a rope instead of a load and vice versa. 

In some cases, the line and load wires may even be the same color. This is where other identification methods come in handy.

Line and load wire identification using position

Line and load wires are specific to wall outlets and switches and have different locations depending on their function within those outlets.

The line is usually located at the bottom of the switch, since it supplies power to it, and the load is usually located at the top of the switch. 

This is another easy way to distinguish between these two wires. However, there can still be confusion. You may not be able to tell which part of the switch is top and which is bottom. 

Also, in a situation that many people may find themselves in, what if the wires are not used and not even connected to the switch? How then can they be accurately identified?

Determination of linear and neutral wires using a non-contact voltage tester

One of the most infallible methods of identifying your line and load wires is to use a non-contact voltage tester.

A non-contact voltage tester is a device that beeps or lights up when its tip comes close to electricity or voltage. This does not depend on whether the copper wires carrying electricity are exposed or not.

Now, when the line and load wires are idle or disconnected from the breaker, or when the breaker is turned off, only one of them is carrying current. This is a line wire.

You simply use the tip of your voltage tester to touch the insulation of each of the wires to be identified. The wire that emits the beep or light is the line wire and the other wire is the load wire.

Using a voltage tester is a safer method than using a multimeter to identify your wires. However, the multimeter is more accessible to everyone as it serves multiple purposes.

Identifying line and load wires with a multimeter

With a multimeter, you must be in contact with bare wires, so you need to be very careful here. Make sure you wear insulated rubber gloves to avoid electrical hazards.

Connect the black negative lead of the multimeter to the "COM" port and the red positive lead to the "VΩmA" port.

Continue turning the multimeter dial to the 200 VAC voltage range, which is represented on the multimeter by the letter "VAC" or "V~".

Now place the black wire on any metal surface nearby, and the red wire on the exposed part of the wires. This means that if they are connected to a switch, you may have to unplug them in order to see those exposed parts.

Alternatively, you can also place your probes on the screws that hold the wires in place on the switch or meter box.

Once you have done all this, the multimeter is expected to show 120 volts on one of the wires. The wire you're getting this reading from is your line, while the other wire that doesn't give any reading is your load wire. 

Like a voltmeter, a multimeter gives the most accurate results. There are no changes that can be made to this.

Line and load wire identification with a neon screwdriver

A neon screwdriver is a tool that works in the same way as a voltage tester, but requires contact with bare wires. This is a screwdriver that emits a normal red light when in contact with electricity.

Place the tip of your neon screwdriver on the exposed wires or on the screws that hold them in place on the switch or meter box. 

The wire that makes the neon screwdriver glow is your line wire and the other is your load wire.

Remember that when performing procedures with a voltmeter, multimeter, or neon screwdriver, the switch must be off. This cuts off power to the circuit (or between the line and the load).

Conclusion

There are several ways to distinguish between line and load wires in a switch.

Using color codes and positioning is easier, but not entirely reliable, while multimeter, voltmeter, and neon screwdriver tests are more reliable.

F.A.Q.

How to identify GFCI line and load wires?

At a GFCI outlet, you use a non-contact voltage tester, a multimeter, or a neon screwdriver to check the voltage on the wires. The wire that has voltage is the line wire and the other is the load wire.

What happens if I reverse the string and upload?

The outlet and electrical appliance still work, but are a potentially lethal electrical shock hazard. This is because the circuit breaker has tripped and the live line wire is no longer connected to ground.