If you’ve ever installed a GFCI outlet or breaker, you’ve probably noticed two terminals labeled “Line” and “Load.” Mixing them up is one of the most common DIY electrical mistakes—and it can render your GFCI useless, leaving you vulnerable to electric shock. In this guide, we’ll clarify what Line and Load mean, how they work, and why getting them right is critical for protecting your home, family, and devices.
What Is a GFCI?
Before diving into Line vs. Load, let’s recap: A GFCI (Ground Fault Circuit Interrupter) is a life-saving device that shuts off power in milliseconds if it detects even a tiny current leak (as little as 5 milliamps)—the difference between a harmless tingle and fatal electrocution. Found in bathrooms, kitchens, garages, and outdoor outlets, GFCIs are legally required in most wet or high-risk areas.
GFCI Line vs Load: The Basics
At their core, Line and Load are terminals that control how power flows through the GFCI. Here’s the simple breakdown:
What Is the “Line” Terminal?
Line refers to the incoming power supply—the wires that bring electricity from your main electrical panel to the GFCI. Think of Line as the “source” terminal: it’s where the GFCI gets its power to monitor for ground faults.
- Wires connected to Line: Typically black (hot) and white (neutral) wires from the main panel. Some GFCIs also have a green ground terminal, but Line specifically handles the live power.
- Job: Feeds power into the GFCI so it can detect faults in both itself and (if Load is used) downstream devices.
What Is the “Load” Terminal?
Load refers to the outgoing power—the wires that carry electricity from the GFCI to other outlets, lights, or devices downstream (after the GFCI). This is what makes GFCIs unique: they can protect not just themselves, but also multiple devices on the same circuit.
- Wires connected to Load: Black (hot) and white (neutral) wires leading to other outlets or fixtures (e.g., a string of bathroom outlets).
- Job: Sends power out from the GFCI, but only if no ground fault is detected. If the GFCI trips, it cuts power to both itself and all Load-connected devices.
Why Line vs. Load Matters: A Real-World Example
Let’s say you’re installing a GFCI outlet in your bathroom. Here’s what happens if you mix up Line and Load:
Correct Wiring (Line In, Load Out)
- Line terminals: Connected to the black/white wires from the main panel.
- Load terminals: Connected to the black/white wires leading to a second bathroom outlet.
- Result: The GFCI protects itself and the second outlet. If you drop a hair dryer in water, the GFCI trips, cutting power to both.
Incorrect Wiring (Load In, Line Out)
- Line terminals: Accidentally connected to the downstream outlet wires.
- Load terminals: Connected to the main panel wires.
- Result: The GFCI won’t protect anything. It might not trip during a ground fault, leaving you at risk of shock. Worse, downstream devices won’t be protected either.
Key Differences at a Glance
| Feature | Line Terminal | Load Terminal |
|---|---|---|
| Purpose | Brings power into the GFCI | Sends power out to downstream devices |
| Connected To | Main electrical panel wires | Other outlets, lights, or devices |
| Protection Scope | Powers the GFCI itself | Extends GFCI protection to Load-connected devices |
| If Miswired | GFCI won’t work at all | GFCI works but doesn’t protect downstream |
How to Identify Line vs. Load Wires
If you’re unsure which wires are Line (incoming) and which are Load (outgoing), here’s how to tell:
1. Check the Electrical Box
- Line wires: Come directly from the wall/ceiling (leading back to the main panel). They’re the “source” wires.
- Load wires: Lead to other outlets or fixtures (e.g., a wire nut connecting to another outlet’s wires).
2. Use a Voltage Tester
- Turn off power at the breaker.
- Disconnect all wires and turn power back on.
- Touch the tester to the black wires: The one with voltage is Line (incoming power). The dead one is Load (outgoing).
3. Read the GFCI Instructions
Most GFCI outlets/breakers have clear diagrams: Line terminals are usually labeled “Line” with a power icon (⚡), while Load has an arrow pointing away (→) to show downstream flow.
Common Mistakes to Avoid
- Skipping the Load Terminal: Even if you don’t have downstream devices, leaving Load terminals empty is fine—just cap the wires with wire nuts. But never connect Line wires to Load!
- Overloading the Load Circuit: The Load terminal powers downstream devices, but GFCI outlets have a maximum load (usually 15–20A). Don’t daisy-chain too many devices on one GFCI.
- Forgetting the Ground Wire: Both Line and Load circuits need a ground wire (green or bare copper) connected to the GFCI’s ground terminal for full protection.
FAQs: Line vs. Load on GFCIs
Q: What happens if I swap Line and Load on a GFCI?
A: The GFCI won’t detect ground faults properly. It might not trip when it should, leaving you unprotected. In some cases, the GFCI itself won’t even power on.
Q: Do I have to use the Load terminal?
A: No! The Load terminal is optional. If you’re only protecting the GFCI itself (not downstream devices), just connect the Line wires and cap the Load wires.
Q: Can I connect multiple devices to the Load terminal?
A: Yes, as long as the total current doesn’t exceed the GFCI’s rating (e.g., 15A for most outlets). A good rule: Limit to 8–10 devices per GFCI.
Q: Does a GFCI breaker have Line and Load terminals?
A: Yes! GFCI breakers (installed in your main panel) also have Line (incoming from the panel) and Load (outgoing to circuits) terminals. The same rules apply: Line = power in, Load = power out.
Final Tip: When in Doubt, Call a Pro
Wiring a GFCI is manageable for DIYers, but Line vs. Load mix-ups are dangerous. If you’re unsure, hire a licensed electrician. A 30-minute visit could save you from a shock or fire.
Post time: Aug-29-2025
