To wire one switch to control two lights, run a 14/2 or 12/2 NM-B power source to the single-pole switch box, connect the incoming hot (black) to one brass terminal, and route a 14/2 or 12/2 cable from the second brass terminal to the first light, then daisy-chain to the second light. Neutrals (white) splice together and bypass the switch. All bare grounds bond to every box and device. WARNING: This involves 120V AC mains. Turn off the breaker, lock the panel, and verify dead with a non-contact voltage tester and multimeter before touching any wires. NEC-style guidance applies; consult your local AHJ.
Decoding the Diagram: Symbols, Terminals, and Box Fill
Before pulling any wire, you need to translate the schematic into physical reality. A standard one switch two lights wiring diagram relies on a specific visual vocabulary. Straight lines represent conductors (wires). A solid black dot where two lines cross indicates a physical splice (wire nut). An open circle with a cross inside represents a light fixture. A single break in the line with a hinged lever denotes a single-pole switch.
Polarity is a critical concept here: the diagram will always show the ungrounded conductor (hot/black) being interrupted by the switch, while the grounded conductor (neutral/white) passes straight through to the silver terminal on the light fixtures. This ensures the fixture is de-energized when the switch is off, preventing shock hazards when changing bulbs.
When planning this circuit, you must calculate box fill to ensure your electrical boxes are large enough to safely dissipate heat and allow for wire bending space. Below is the specification and box fill data for a standard 15A residential lighting circuit using 14 AWG copper wire.
| Component / Location | Specification / Value | NEC Reference | Purpose in Circuit |
|---|---|---|---|
| Power Source Cable | 14/2 NM-B (with ground) | NEC 310.16 | Feeds 120V ungrounded (hot) and grounded (neutral) to the switch box. |
| Switch to Light 1 Cable | 14/2 NM-B (with ground) | NEC 300.3 | Carries the switched hot and the pass-through neutral to the first fixture. |
| Light 1 to Light 2 Cable | 14/2 NM-B (with ground) | NEC 300.3 | Daisy-chains the switched hot and neutral to the second fixture. |
| Single-Pole Switch | 15A / 120V AC (e.g., Leviton 5601) | NEC 404.14 | Interrupts the hot leg only; rated for 15A resistive lighting loads. |
| Switch Box Min. Volume | 18 cubic inches | NEC 314.16 | Accommodates 2 cables (4 current-carrying wires), 1 device, and grounds. |
| Light Box Min. Volume | 12 cubic inches (per box) | NEC 314.16 | Accommodates 2 cables and fixture wires without crowding. |
Node-by-Node Trace: Source to Switch to Loads
Abstract diagrams can be confusing on the jobsite. Let us trace the current path node-by-node, from the breaker panel to the final fixture, explicitly calling out the equipment grounding conductor (EGC) path.
- Node 1: The Breaker Panel. A 15A single-pole breaker supplies 120V AC. The black (hot) and white (neutral) wires exit the panel via the 14/2 source cable. The bare copper ground bonds to the panel's ground bus bar.
- Node 2: The Switch Box (Line Side). The source cable enters the switch box. The white neutral bypasses the switch entirely, splicing directly to the white neutral of the outgoing cable heading to Light 1. The black hot wire lands on the switch's Line (brass) terminal. The bare copper ground splices to the box ground pigtail and the outgoing ground wire.
- Node 3: The Switch (Load Side). When the toggle is flipped ON, the internal contacts close. The 120V potential transfers from the Line terminal to the Load terminal, energizing the black wire of the cable heading to Light 1.
- Node 4: Light Fixture 1. The cable from the switch enters the first ceiling or wall box. The black switched-hot connects to the black lead of the light fixture. The white neutral connects to the white fixture lead. The bare ground connects to the fixture's green ground screw. Crucially, this box also acts as a splice point: pigtails connect the incoming black, white, and bare wires to the outgoing 14/2 cable heading to Light 2.
- Node 5: Light Fixture 2. The daisy-chain cable enters the second box. The black wire connects to the second fixture's black lead, the white to the white lead, and the bare copper to the green ground screw. The circuit ends here.
The Ground Path (Equipotential Bonding): The bare copper EGC never passes through a switch or fixture's internal switching mechanism. It forms a continuous, unbroken safety net. From the panel, it bonds to the metal switch box (if metal), pigtails to the switch's green screw, and continues via wire nut splices in every light box to bond to every fixture canopy and metal housing. If a hot wire chafes against a metal box, this path provides the low-impedance route that instantly trips the breaker. For comprehensive safety protocols on de-energizing panels before working on these paths, refer to OSHA's hazardous energy control guidelines.
Physical Wiring Steps & Terminal Mapping
When you are standing in front of the physical device, the schematic symbols translate to specific brass, silver, and green screws. Here is the exact terminal mapping for a standard single-pole switch like the Leviton 5601.
| Physical Terminal | Screw Color | Function | Wire Connected |
|---|---|---|---|
| Terminal 1 (Line) | Brass | Unswitched Hot Input | Black wire from power source |
| Terminal 2 (Load) | Brass | Switched Hot Output | Black wire heading to Light 1 |
| Terminal 3 (Ground) | Green | Equipment Ground | Bare copper pigtail from box splice |
Note: On a standard single-pole switch, the two brass terminals are electrically interchangeable. You can connect the Line hot to either brass screw and the Load hot to the other. (This is not true for 3-way switches, where the black "common" screw is strictly for the line or load).
Execution Steps:
- Prep the Wires: Strip exactly 3/4 inch of insulation from the 14 AWG solid copper wires. Use the strip gauge molded into the back of the switch yoke to verify length. Too much exposed copper creates a shock hazard; too little causes the screw to bite the insulation, leading to a high-resistance fault and melted terminal.
- Bond the Grounds: In the switch box, twist the two bare copper wires together with a 6-inch bare copper pigtail. Secure with a gray or green wire nut. Attach the pigtail to the switch's green screw.
- Splice the Neutrals: Push the two white neutral wires and a 6-inch white pigtail into a red or yellow wire nut. Do not connect this pigtail to the switch. Fold it neatly into the back of the box. (If you are using a smart switch or timer that requires a neutral, this pigtail will connect to the switch's white/neutral lead).
- Terminate the Hots: Form a shepherd's hook in the black source wire and loop it clockwise around the first brass screw. Tighten to 12-14 inch-pounds. Repeat for the black load wire on the second brass screw.
- Tuck and Mount: Fold the ground wires into the back of the box first, followed by the neutrals, and finally the hots. Mount the switch using the provided 6-32 machine screws, ensuring the yoke sits flush against the drywall or plaster ear.
Multimeter Verification & Troubleshooting
Never assume a circuit is wired correctly just because the lights turn on. A miswired neutral or a shared ground can create hidden hazards. Use a digital multimeter (DMM) to verify your work. For detailed box fill and wire routing calculations to ensure your physical layout matches the diagram, consult EC&M's guide on NEC box fill calculations.
Test 1: Continuity Check (Power OFF, Breaker Locked Out)
- Set your DMM to the continuity or resistance (Ohms) setting.
- Place one probe on the switch's Line brass terminal and the other on the Load brass terminal.
- Flip the switch ON. The meter should read < 1 ohm (or beep continuously).
- Flip the switch OFF. The meter should read "OL" (Open Loop) or infinite resistance.
- Place one probe on the brass terminal and one on the green ground screw. It must read "OL" regardless of switch position. If it reads continuity, the switch is internally shorted to ground and must be discarded.
Test 2: Voltage and Polarity Check (Power ON)
- Set your DMM to AC Voltage (V~), expecting a range of 114V to 126V.
- Turn the switch ON. Place the black probe on the Load brass terminal and the red probe on the grounded metal box (or the bare ground wire). You should read ~120V.
- Turn the switch OFF. The reading should drop to 0V. If it reads ~120V when OFF, your switch is either wired backward (if using a 3-way by mistake) or internally fused.
- At Light Fixture 1 (with switch ON), measure between the black fixture lead and the white fixture lead. You should read ~120V. Measure between the white fixture lead and the bare ground. You should read < 2V. If you read 120V between neutral and ground, you have an open neutral or a crossed neutral/ground fault upstream.
Troubleshooting: Light 1 Works, Light 2 is Dead
If the first light illuminates but the second does not, the issue is isolated to the daisy-chain splice at Light Fixture 1. Turn off the breaker and open the Light 1 canopy. Check the wire nut connecting the incoming black wire, the fixture's black lead, and the outgoing black wire to Light 2. A common mistake is failing to strip the outgoing wire, leaving insulation trapped under the wire nut, or failing to tug-test the wires, resulting in a loose connection that arcs and fails under load. Re-strip, re-twist, and secure the splice.
