Line vs Load Wire: What You Need To Know

If you're planning an electrical project—whether it's installing a GFCI outlet, replacing a breaker, or upgrading your electrical panel—understanding the difference between line vs load wires is critical. These terms aren't just technical jargon—they affect how power flows through your system, the safety of your setup, and the functionality of your devices.


At A&R Electric Louisiana, we help homeowners and business owners alike make informed decisions when it comes to their electrical systems. In this guide, we’ll explain what line and load wires are, how to identify them, common use cases, and why mixing them up can be dangerous.

What Does Line vs Load Mean?


At its core, "line vs load" refers to the direction in which electricity flows through a circuit.



  • Line wire brings incoming power from your electrical service panel or breaker box.

  • Load wire sends electricity out from the device to power downstream outlets or fixtures.

You’ll often hear this terminology used when dealing with GFCI outlets, smart switches, breakers, or surge protectors—essentially any device that sits in the middle of an electrical pathway.


What Is a Line Wire?


The line wire is the live wire that feeds power directly from the electrical panel. It's the source of electricity and is always "hot" unless turned off at the breaker.


Key Traits of a Line Wire:


  • It carries incoming power from the service panel.

  • It is typically connected to the top terminal in outlets or switches.

  • It supplies energy to the device where it is connected.

If you connect a device to the wrong terminal thinking it’s the line, it may not work—or worse, it may seem off but still be energized and dangerous to touch.


What Is a Load Wire?


The load wire carries power from a device to another device further down the line. In simpler terms, it allows you to daisy-chain multiple outlets, lights, or appliances while protecting everything downstream.


Key Traits of a Load Wire:


  • It delivers power to additional devices after the one you're wiring.

  • It is usually connected to the bottom terminal in switches or GFCI outlets.

  • It may only be energized when the upstream device is working properly.

So if you're installing a GFCI outlet and want it to protect outlets further down the line, you would connect those downstream wires to the load terminals.


Line vs Load: Why It Matters


Understanding line versus load is crucial for both safety and functionality. Connecting the wrong wire to the wrong terminal can result in:


  • Loss of protection: GFCI outlets won't protect downstream outlets if the line/load configuration is incorrect.

  • Device failure: Smart switches or receptacles may not function as intended.

  • Electrical hazards: Miswiring can leave a seemingly dead outlet energized, increasing the risk of electric shock.

In short, misidentifying line and load wires can cause damage to your electrical system—or worse, put you or your property at risk.


Where You'll Encounter Line and Load Wires


1. GFCI Outlets


These Ground Fault Circuit Interrupter outlets have clearly marked terminals for line and load connections. The line side is where power enters; the load side allows you to protect other outlets.


2. Smart Switches and Dimmers


Smart home devices often need to know where the power is coming from and going to. Line goes to the switch, while load connects to the light or fixture being controlled.


3. Circuit Breakers


In some breaker panel setups, the breaker is connected to the line side and feeds circuits through the load wires to devices or outlets throughout your home.


4. Surge Protectors


Whole-house surge protectors or advanced panels rely on correct line/load wiring to safeguard your appliances and electronics.


How to Identify Line and Load Wires


Correct identification is essential before making any connections. Here’s how to distinguish between them:


Use a Voltage Tester


  • Turn off power at the breaker box before working on any wires.

  • Disconnect both sets of wires.

  • Turn the power back on and carefully use a non-contact voltage tester or multimeter to test for voltage.

  • The wire showing voltage is your line wire.

  • The other one—without power unless the device is activated—is the load wire.

Check Labels


Manufacturers often label terminals in GFCI outlets or switches:


  • LINE = Incoming power (from the panel)

  • LOAD = Outgoing power (to other devices)

If there's no label, refer to the instruction manual or consult a licensed electrician.


Common Mistakes When Wiring Line vs Load


1. Reversing Terminals on GFCIs


If you wire a GFCI backward—putting the incoming power on the load side—the outlet may appear to work, but downstream protection is lost. Worse, it may leave other outlets hot even if the GFCI trips.


2. Assuming Top or Bottom = Line


While many outlets are designed with line on top and load on bottom, this is not universal. Always verify before wiring.


3. Skipping Testing


Failing to confirm which wire is hot can lead to improper installation and dangerous outcomes. Testing should never be skipped.


Load vs Line: Practical Use Cases


Let’s look at some real-life examples to reinforce why knowing load vs line matters.


Scenario 1: Installing a GFCI in a Kitchen


You install a GFCI to protect two more outlets in the same circuit. The first GFCI must be connected with the incoming power on the line side, and the outgoing wires (to other outlets) on the load side. This ensures that if the GFCI trips, the other two outlets will shut off too.


Scenario 2: Replacing a Light Switch with a Smart Switch


A smart switch requires the line wire to be correctly connected to ensure constant power for Wi-Fi functionality. The load wire connects to the light fixture itself. If reversed, the switch may malfunction or not work at all.

Line vs Load in Troubleshooting


Understanding line and load also helps during diagnostics. For example, if you're troubleshooting a dead outlet or tripped breaker:


  • Check the line side to ensure power is being delivered.

  • Check the load side to ensure the device is passing power correctly.

  • A failed GFCI may not let power pass to the load side, leaving downstream outlets dead.


Safety First: When to Call a Professional


Electrical work is not a DIY experiment. If you're unsure about identifying line vs load wires or lack the proper tools, it’s always best to leave it to professionals.


At A&R Electric Louisiana, our licensed electricians provide accurate diagnostics, safe installations, and thorough testing for all your wiring needs—residential or commercial. Our team ensures your systems are compliant with code, correctly wired, and fully functional.


Final Thoughts on Line vs Load


Knowing the difference between line vs load wires is more than just technical trivia—it’s a foundational element of electrical safety and performance. From powering outlets to protecting entire circuits, how you connect these wires determines whether your home’s electrical systems run smoothly or face hidden dangers.


Whether you’re replacing a switch, upgrading an outlet, or planning a more complex renovation, take the time to verify which wire is which. And if in doubt, don’t guess—call a licensed electrician.


Need help with your electrical wiring project?
Let the professionals at A&R Electric Louisiana take the guesswork out of your installation. From diagnosing load vs line issues to upgrading entire panels, we offer expert service you can trust.


Contact us today for a consultation or to schedule your next electrical service.