A load wire is the conductor that carries electrical current away from a switch, receptacle, or breaker toward the downstream device or appliance consuming the power. If you are asking what color wire is the load, the direct answer is that the National Electrical Code (NEC) does not assign a unique color exclusively for load conductors; instead, load wires use the same colors as the line (hot) wires—typically black, red, or blue—depending on the circuit phase and wiring method.
Unlike the grounded neutral (white) or the equipment ground (bare/green), the load wire is simply the continuation of the ungrounded hot conductor. In a standard residential branch circuit, identifying the load wire correctly is critical for ensuring downstream protection on GFCI/AFCI devices and proper operation of smart switches. Below, we break down exactly how to identify, size, and terminate load conductors based on current NEC guidelines.
Line vs. Load: What Changes in the Circuit?
To understand the load wire, you must distinguish it from the line wire. The line wire brings power from the source (the breaker panel or an upstream device). The load wire carries power away from the current device to the next destination. Think of the line as the main water feed entering a room, and the load as the branch pipe continuing to the next sink.
What does distinguishing line from load actually change in a real installation? For a standard single-pole switch or a standard duplex receptacle, the device does not care which side the line and load are connected to; current flows bidirectionally through the brass terminals. However, for protective and electronic devices, line and load are strictly directional:
- GFCI and AFCI Receptacles: These devices monitor the current differential between line and load. If you connect downstream outlets to the LINE terminals instead of the LOAD terminals, those downstream outlets will not receive ground-fault protection.
- Smart Switches and Dimmers: Electronic switches contain internal relays and power supplies. Reversing line and load can cause the switch to remain permanently energized, fail to dim, or destroy the internal triac.
- Meter Sockets and Main Disconnects: Utility power enters the line lugs; the bus bars feed out through the load lugs to the branch breakers.
Standard Wire Colors for Load Conductors (NEC Guidelines)
Because the load wire is an extension of the hot line wire, it follows the NEC color rules for ungrounded (hot) conductors. According to NFPA 70 (NEC) Article 210 and Article 404, here is how load wires are colored across common residential scenarios:
| Wiring Scenario | Load Wire Color | NEC Rule / Convention |
|---|---|---|
| Daisy-chained Receptacle (120V) | Black | Matches the line hot color; continues the 120V ungrounded conductor to the next outlet. |
| Switch Loop (Power at the light) | White (Re-identified) | NEC 200.7(C)(2) requires a white wire used as a hot load return to be painted or taped black/red at both ends. |
| Multi-wire Branch Circuit (MWBC) | Red or Blue | Used for the second phase (240V split-phase) load continuation to ensure opposite legs share a neutral. |
| 3-Way Switch Traveler/Load | Red, Black, or Blue | Travelers carry the load between switches; the final load to the fixture is typically black. |
A Worked Numeric Example: Sizing and Terminating a 15A GFCI Load
Let us look at a real-world installation to see how line and load interact with wire sizing and terminal specifications. Suppose you are installing a 15A GFCI receptacle in a bathroom to protect a downstream standard receptacle near the mirror.
- Breaker: 15A single-pole AFCI/GFCI breaker at the panel.
- Wire: 14 AWG NM-B (Romex) copper cable. Per NEC Table 310.16, 14 AWG copper is rated for 15A in the 60°C temperature column, which is the standard rating for residential receptacle terminals.
- Voltage: 120V nominal (acceptable operating range 114V–126V).
The Wiring Sequence:
- Identify the Line: Using a non-contact voltage tester, identify the black wire carrying 120V from the panel. Strip 5/8 inch of insulation.
- Terminate Line: Connect the line black wire to the brass screw marked LINE. Connect the line white wire to the silver screw marked LINE.
- Prepare the Load: The black and white wires continuing to the mirror outlet are your LOAD conductors. Strip 5/8 inch of insulation.
- Terminate Load: Connect the downstream black wire to the brass screw marked LOAD. Connect the downstream white wire to the silver screw marked LOAD.
- Torque Specification: Using a calibrated torque screwdriver, tighten the terminal screws to the manufacturer's specification—typically 14 in-lbs for Leviton GFCI devices. Under-torquing causes arcing; over-torquing strips the brass threads.
In this scenario, both the line black wire and the load black wire are exactly the same color and gauge (14 AWG black). The only difference is their physical direction: one comes from the breaker, the other goes to the next outlet.
Where You Meet This in Practice
While standard switches forgive line/load reversals, modern electrical work constantly forces you to identify the load wire correctly. Here is where confusing line and load causes the most headaches on the jobsite:
1. Smart Switches Requiring a Neutral
Most Wi-Fi and Z-Wave smart switches (like Lutron Caséta or Kasa Smart) require a neutral wire to power their internal radios. If you mistake a load wire for a neutral wire and connect it to the switch's neutral terminal, you will create a direct short circuit through the downstream light fixture the moment the switch closes, instantly destroying the smart switch's internal fuse.
2. Old Switch Loops (Pre-2011 NEC)
In older homes, power often went to the light fixture first, and a single 2-wire cable (black and white) was dropped down to the switch. The white wire was used as the hot line down to the switch, and the black wire was used as the hot load back up to the light. Because the white wire was acting as a hot conductor, it was supposed to be wrapped in black electrical tape. If you are replacing a switch in an older home and see a white wire connected to a brass screw, treat it as a hot line or load wire, never a neutral.
3. Troubleshooting Dead Downstream Outlets
If a standard outlet in a bedroom is dead, but the breaker is on, the issue is often a failed "load" connection at the upstream GFCI or a backstabbed receptacle. The load wire has simply lost continuity. Tracing the load wire from the last known working outlet is the standard diagnostic path.
Frequently Asked Questions
What color is the load wire on a GFCI outlet?
The load wire on a GFCI outlet is the same color as the line hot wire—almost always black for standard 120V circuits, or red if it is carrying the second leg of a 240V multi-wire branch circuit. The GFCI receptacle itself uses brass-colored screws for the hot load terminal and silver-colored screws for the neutral load terminal. Always look for the "LOAD" sticker on the plastic housing next to the terminal block.
Can I use a white wire as a load wire in a switch loop?
Yes, but only if you re-identify it. According to NEC 200.7(C)(2), if a white wire is used as an ungrounded (hot) conductor—such as a load wire returning from a switch to a light fixture—it must be permanently re-identified at both ends with black or red paint, or wrapped in black/red electrical tape. This warns future electricians that the white wire is carrying line voltage, not acting as a neutral.
What happens if I wire line and load backwards on a standard switch?
Electrically, nothing happens. A standard single-pole mechanical switch simply bridges two brass terminals; current flows through it in either direction. The light will turn on and off normally. However, it is considered poor practice because it violates standard wiring conventions, which can confuse future troubleshooters who expect the line to enter the bottom terminal and the load to exit the top.
How do I test which wire is the line and which is the load?
Turn off the breaker, disconnect the wires from the device, and separate them so they are not touching. Turn the breaker back on and use a non-contact voltage tester (NCVT) or a multimeter. The wire that registers 120V (or lights up the NCVT) is the line wire bringing power from the panel. The wire that registers 0V is the load wire going to the downstream fixture or outlet. Always verify your meter is functioning on a known live source before and after testing, as recommended by OSHA electrical safety guidelines.
