The LINE terminals on a GFI (Ground Fault Interrupter) receptacle receive incoming power from the breaker panel, while the LOAD terminals pass that power and ground-fault protection to downstream outlets on the same circuit. If you are staring at the back of a 15A or 20A receptacle wondering which screws to use, this single sentence dictates your entire wiring strategy. Getting it wrong doesn't just break the circuit; it can leave downstream devices dangerously unprotected or cause the receptacle to refuse to reset.
LINE vs LOAD Terminal Specifications (Standard 120V 20A Receptacle)
| Feature | LINE Terminals | LOAD Terminals |
|---|---|---|
| Primary Function | Receive incoming 120V AC from the branch circuit breaker | Feed power to subsequent standard receptacles downstream |
| Internal Sensor Path | Current passes into the toroidal current transformer | Current returns out of the toroidal current transformer |
| Downstream Protection | N/A (Source of power) | Extends Class A (4-6mA) ground-fault protection downstream |
| Wire Connection Rule | Must be connected for the GFCI to function and reset | Optional; leave empty if protecting only the local device |
| Max Continuous Current | 16A (80% rule for 12 AWG THHN on a 20A breaker) | 16A (shared cumulatively with LINE loads) |
The Core Difference: LINE vs LOAD in a 120V Circuit
To understand what wiring to the LOAD terminals actually changes in a real installation, you have to look inside the device. A GFI receptacle contains a differential current transformer (a toroidal iron core). The internal hot and neutral conductors pass directly through the center of this donut-shaped core.
When you wire a downstream outlet to the LOAD terminals, the current flowing to that downstream outlet must travel through the GFCI's internal sensor. If a ground fault occurs at the downstream outlet, the sensor detects the missing current and trips the entire circuit. If you instead pigtail the downstream outlet directly to the LINE terminals (bypassing the LOAD screws), the downstream outlet gets power, but its current never passes through the GFCI's sensor. It will have zero ground-fault protection.
What People Commonly Confuse This With
- Confusing LOAD with Ground: Novices sometimes assume the "LOAD" terminal is for the equipment grounding conductor. It is not. The bare copper or green wire always goes to the green grounding screw. LOAD is strictly for the current-carrying neutral (silver) and hot (brass) conductors feeding the next device.
- GFI vs. GFCI Terminology: People often ask if a "GFI" is different from a "GFCI". In residential and commercial wiring, they are functionally identical. GFCI (Ground Fault Circuit Interrupter) is the formal NEC (NFPA 70) terminology, while GFI is an older, colloquial abbreviation still stamped on some device faces and used by veteran electricians.
- The "Pass-Through" Myth: Many DIYers assume LOAD is just a convenient set of extra screws to daisy-chain power. It is not a passive pass-through; it is an active, monitored extension of the protection circuit.
Worked Numeric Example: A 20A Bathroom Branch Circuit
Let's look at a real-world numeric scenario to see how the LINE and LOAD terminals handle current and faults.
The Loads: You plug a 14A hair dryer directly into the GFCI (drawing through the LINE side internally). You plug a 2A exhaust fan into the downstream standard receptacle (drawing through the LOAD terminals). The total circuit draw is 16A, well within the 20A breaker limit and the 16A continuous rating of the 12 AWG wire.
The Fault Event: The exhaust fan's internal insulation degrades, and 6mA of current leaks from the hot winding to the grounded metal housing.
The Math and the Trip:
1. The LINE hot conductor carries 16A out from the panel.
2. The hair dryer returns 14A on the internal neutral.
3. The downstream fan should return 2A on the LOAD neutral, but because of the fault, it only returns 1.994A (2A minus the 0.006A leakage to ground).
4. The GFCI's toroidal sensor sees 16A going out, but only 15.994A coming back.
5. The sensor detects the 6mA (0.006A) imbalance. According to OSHA and UL 943 standards, a Class A GFCI must trip at 5mA ±1mA. The internal silicon-controlled rectifier (SCR) fires, tripping the mechanical latch in under 25 milliseconds, cutting power to both the hair dryer and the fan before the leakage can cause a lethal shock.
Where You Meet This in Practice: Multi-Outlet Feed-Through
You will encounter LINE and LOAD decisions primarily in areas where the NEC mandates ground-fault protection for multiple receptacles on a single branch circuit. This is known as "feed-through" protection.
- Bathrooms: A single 20A GFCI at the first outlet position can protect all subsequent standard receptacles in the same bathroom via the LOAD terminals. (Note: It cannot protect receptacles in a different bathroom under current NEC rules).
- Kitchen Countertops: Small-appliance branch circuits often use a GFCI at the start of the counter run, feeding through to standard duplex outlets further down the counter.
- Garages and Outdoors: A single GFCI in the garage panel area might feed through to exterior weather-resistant (WR) receptacles under the eaves.
The Feed-Through Rating Caveat: Not every GFCI is legally rated to protect downstream devices. Before wiring to the LOAD terminals, look at the face or the back of the receptacle. You must see the printed text: "FOR GFCI PROTECTION OF DOWNSTREAM CIRCUITS" or "FEED-THROUGH". If a device lacks this marking (common in some specialized industrial or older 2-pole GFCIs), the LOAD terminals are strictly for mechanical daisy-chaining and do not extend fault protection. Always verify the manufacturer's spec sheet.
Troubleshooting FAQ: Swapped Connections and Reset Failures
When a GFCI refuses to cooperate, the LINE/LOAD relationship is almost always the culprit. Here is how to diagnose the most common bench and jobsite failures.
Why won't my new GFCI reset out of the box?
Modern GFCIs (manufactured after the mid-2000s) feature built-in miswire protection. If you accidentally connect the incoming panel power to the LOAD terminals and leave LINE empty, the internal sensing circuit detects that the hot wire is on the wrong side of the toroid. It physically blocks the reset button from latching. The fix: Turn off the breaker, swap the wires so the incoming power is on LINE, and try again.
The GFCI resets, but the downstream outlets don't work. What happened?
You likely have a broken neutral connection on the LOAD terminal, or the downstream cable was wired to the LINE terminals via a pigtail, but the hot wire was dropped. If you want the downstream outlet to work and be protected, the downstream cable's hot and neutral must be securely clamped under the LOAD brass and silver screws, respectively. Torque the terminal screws to the manufacturer's spec (usually around 14-16 in-lbs for 12 AWG) to prevent cold solder joints or arcing.
I want to daisy-chain power to the next outlet, but I DON'T want it GFCI protected. How?
If local code or a specific appliance requirement (like a dedicated sump pump or medical freezer) dictates that the downstream device must not be on a GFCI, you cannot use the LOAD terminals. You must use a wire nut to pigtail the incoming panel wires and the outgoing downstream wires together, and then connect a single short jumper wire from that bundle to the LINE terminals of the GFCI. The LOAD terminals remain completely empty and capped with electrical tape.
