How To Identify Line And Load 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 identify if your line and load wires are connected with the right polarity?

No one wants to be at risk of fatal shock hazards and if your answer to these is yes, then you have come to the right place.

Our article presents you whole process of how to identify line and load wires.

Let’s get right in.

how to identify line and load wires

What Are Line And Load Wires

“Line” and “Load” are terms used in electrical connections that involve a device receiving and sending out current to other devices.

The line wire is the upstream wire coming from the main power source that supplies power to the receptacle.

It is always hot (always carries current) when there is power supply from the power source. 

The load wire, on the other hand, is the downstream wire that takes current away from the receptacle and supplies it to other electric devices. It is only hot when the receptacle switch is turned on (signaling a closed circuit that allows current to flow through).

There is usually a third wire, which is an idle ground connection that specifically works with the line wire and protects against fatal electric shocks.

A bad connection of the line and load in a GFCI socket wiring in your house, for example, makes its circuit breaker useless and presents you with a fatal shock hazard.

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

Tools Required To Identify Line And Load Wires

The tools required to identify your line and load wires include

  • A multimeter
  • Multimeter probes
  • Non contact voltage tester
  • Neon screwdriver

These help to provide more accurate results.

How To Identify Line And Load Wires

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

There is more to these identification methods as well as other ways you may identify the line and load wires. We will get into them now.

line and load wires

Identifying Line And Load Wires Through Color

The easiest way to distinguish between your line and load wires is through the use of color codes. 

Generally, wires are insulated with rubber to safeguard us from electrical shock hazards. These rubber insulation also come in a barrage of colors and have a specific meaning to them.

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

However, there’s still an issue. Since the color of the wire doesn’t have anything to do with whether they work or not, color codes may be interchanged.

For instance, the red rubber may be alternatively used for the line instead of the load and vice versa. 

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

Identifying Line And Load Wires Using Position

The line and load wires are peculiar to wall outlets and switches and have different positioning due to their functions within these receptacles.

The line is usually positioned at the bottom of the switch as it supplies power to it, while the load is usually positioned at the top of the switch. 

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

Additionally, as a situation many people may find themselves in, what if the wires are idle and not even connected to a switch in the first place? How then do you accurately identify them?

Identifying Line And Neutral Wires Using A Non contact Voltage Tester

One of the most unfailing methods of identifying your line and load wires is with the use of a non contact voltage tester.

A non contact voltage tester is a device that gives off a beep or illuminates a light when its tip comes close to electricity or voltage. This is regardless of whether the copper wires carrying the electricity are exposed or not.

Now, when the line and load wires are idle or disconnected from the switch, or when the switch is turned off, only one of them carries current. This is the 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 gives off a beep or light is your line wire and the other wire is your load wire.

Making use of a voltage tester is a safer method than making use of a multimeter to identify your wires. Nonetheless, the multimeter is more readily available to everyone as it serves a variety of purposes.

Identifying Line And Load Wires Using A Multimeter

With the multimeter, you have to make contact with exposed wires, so you want to be really careful here. Make sure you wear insulated rubber gloves to avoid shock hazards.

Plug your black negative multimeter probe into the “COM” port and plug your red positive probe into the “VΩmA” port.

Proceed to turn the multimeter dial to the 200 AC voltage range which is represented by “VAC” or “V~” on the multimeter.

Now, place the black lead on any metal surface close by and place the red lead on an exposed part of your wires. This means that if they are connected to a switch, you may have to disconnect them to see these exposed parts.

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

Once you do all these, the multimeter is expected to present a 120 volt reading on one of the wires. The wire you get this reading from is your line while the other wire that doesn’t give any reading is your load wire. 

Just like the volt tester, the multimeter also gives you results that are as accurate as possible. There are no changes that may be made to this.

Identifying Line And Load Wire Using A Neon Screwdriver

A neon screwdriver is a tool that works just like the volt tester but requires contact with exposed wires. It is a screwdriver that gives off a common red light when in contact with electricity.

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

The wire that makes the neon screwdriver illuminate is your line wire while the other is your load wire.

Remember that when carrying out procedures with your volt tester, multimeter, or neon screwdriver, the switch is expected to be turned off. This cuts off the power supply within the circuit (or between line and load).


There are multiple methods of differentiating between the line and load wires in a switch.

Using color codes and positioning is easier but isn’t entirely reliable, while the multimeter, volt tester, and neon screwdriver tests are more dependable.

Frequently Asked Questions

How Do You Identify The Line And Load Wires Of A GFCI?

In a GFCI socket, you use a non contact voltage tester, multimeter, or neon screwdriver to check for voltage from the wires. The wire that has voltage is your line wire and the other is your load wire.

What Happens If I Reverse Line And Load?

The outlet and electrical appliance still work but hold a potentially fatal shock hazard. This is because the circuit breaker is disabled and the live line wire isn’t connected to ground anymore.

Alex Klein Author


Alex Klein is an electrical engineer with more than 15 years of expertise. He is the host of the Electro University YouTube channel, which has thousands of subscribers.