Light Switch Wiring Diagram: Single-Pole Switch Connections

A single-pole light switch is the most common electrical device in residential wiring. It interrupts the hot conductor to a fixture -- nothing more. But a surprising number of DIY mistakes trace back to confusing the two main wiring methods (power-to-switch vs. power-to-fixture), misreading wire colors in a switch loop, or missing the NEC neutral-in-box requirement that has applied to new construction since 2011. This guide covers both methods, when you will encounter each, and how to wire them correctly.

How a Single-Pole Switch Works

A single-pole switch has two screw terminals (plus a ground) and controls one circuit from one location. It simply connects or disconnects the hot conductor. When the switch lever is up and ON, the contacts are closed and current flows to the fixture. When the lever is down and OFF, the hot conductor is interrupted.

The switch must be wired in series with the hot (black) conductor only. The neutral (white) wire must never be interrupted by a switch -- breaking the neutral while leaving the hot connected would leave the fixture socket energized even when the switch is off, which is dangerous.

Wire Color Code (US/NEC)

Standard 14/2 or 12/2 NM-B cable contains:

• Black: Hot (ungrounded conductor)
• White: Neutral (grounded conductor)
• Bare copper: Equipment ground

In a switch loop (see Method 2 below), the white wire is repurposed as a hot conductor and must be re-identified with black tape or paint at each visible end.

Method 1: Power-to-Switch (Most Common in Modern Wiring)

In this configuration, the power source cable (from the panel) runs to the switch box first, and a second cable runs from the switch box to the fixture.

Cable Layout

• Cable 1: 14/2 from panel to switch box (power in)
• Cable 2: 14/2 from switch box to fixture (switch leg out)

Wiring Steps

At the switch box:

1. The incoming black (hot) wire from the panel connects to one of the switch's brass screws (either screw -- single-pole switches are not polarized between the two hot terminals).
2. The outgoing black wire (going to the fixture) connects to the other brass screw.
3. The incoming white (neutral) wire and the outgoing white (neutral) wire connect together with a wire connector -- they pass straight through the box without connecting to the switch.
4. All ground wires (bare copper) connect together and a pigtail connects to the switch's green ground screw.

At the fixture:

1. The black wire connects to the black (or brass-terminal) fixture wire.
2. The white wire connects to the white (or silver-terminal) fixture wire.
3. The bare ground connects to the fixture ground wire or green screw.

This method is cleanest -- neutral is always present in the switch box, which satisfies the 2011 NEC requirement for neutral at switch locations and makes smart switch installation straightforward.

Method 2: Power-to-Fixture (Switch Loop)

In older homes, the power sometimes ran to the ceiling box first, and a separate cable dropped down the wall to the switch. This is called a switch loop.

Cable Layout

• Cable 1: 14/2 from panel to fixture box (power in at ceiling)
• Cable 2: 14/2 from fixture box down to switch box (switch loop)

How It Works

The switch loop cable carries both the switched hot (down to switch and back) in a 2-conductor cable:

• The white wire in the switch loop cable runs from the fixture box HOT to the switch (acting as the unswitched hot going down to the switch). It must be re-identified with black tape or marker at both ends.
• The black wire in the switch loop cable carries the switched hot back from the switch to the fixture.

Wiring Steps

At the fixture box:

1. Connect the incoming black (hot) from the panel to the re-identified white wire of the switch loop cable (tape this wire black at both ends).
2. Connect the black wire of the switch loop cable to the fixture's black (hot) lead.
3. Connect the incoming white (neutral from panel) to the fixture's white lead.
4. Connect all grounds together and to the fixture ground.

At the switch box:

1. The re-identified white wire (now treated as hot) connects to one switch terminal.
2. The black wire connects to the other switch terminal.
3. No neutral is present in a traditional switch loop box -- this is why smart switches that require a neutral cannot be installed without rewiring.
4. Connect the bare ground to the switch's green screw.

The 2011 NEC Neutral Rule

Section 404.2(C) of the 2011 NEC requires that a neutral conductor be present in all new switch boxes, not just connected to the switch, but present and available. The switch loop method does not provide a neutral at the switch box. For new construction and renovations requiring permits after 2011, power-to-switch wiring (Method 1) is the compliant approach. Existing switch loops in older homes remain legal to leave as-is when replacing a switch.

Safety First

Turn off the circuit breaker before any work on a switch or fixture. Use a non-contact voltage tester to verify the circuit is dead -- test at the switch box before touching any wires. Test more than once.

Do not assume the white wire is neutral. In a switch loop, the white wire is re-identified as hot. Always verify with a voltage tester.

Ground connections are required. NEC 404.9(B) requires all replacement switches to be grounded. If you are replacing an ungrounded switch in an old box, the switch must either be a grounding type connected to the metal box via a bonding jumper, or GFCI-type switches may be permitted in some situations.

Choosing Wire Gauge

• 15A circuit breaker: Use 14 AWG wire (14/2 NM-B cable). The NEC does not permit 15A circuits to use smaller wire.
• 20A circuit breaker: Use 12 AWG wire (12/2 NM-B cable).

Mixing wire gauges on the same circuit -- for example, splicing 14 AWG onto a 12 AWG/20A circuit -- creates a hazard. The 14 AWG section becomes the weakest point and can overheat at currents the breaker will not trip at.

Single-Pole vs. 3-Way Switches

A single-pole switch controls one light from one location. If you need to control a light from two locations (top and bottom of stairs, both ends of a hallway), you need 3-way switches -- a different wiring method entirely. See our 3-way switch wiring guide for that configuration.

For three or more control points, 4-way switches are added between the two 3-way switches.

Common Mistakes

Switching the neutral instead of the hot: Wiring the white (neutral) through the switch while leaving the black (hot) connected to the fixture permanently. The light works correctly, but the socket is energized when the switch is off -- a shock hazard when changing bulbs.

Connecting the neutral to the switch terminal: In the power-to-switch method, the neutral wires should be joined together in the box, not connected to the switch. A neutral connected to the switch terminal creates an unintended path.

No ground on the switch: Replacing an old ungrounded switch without bonding the ground to the box. NEC requires grounded switches.

Switch loop with no re-identification: Leaving the white switch loop wire unmarked. A future electrician -- or you -- may assume it is neutral and receive a shock when the circuit is live.

Wrong wire gauge: Using 14 AWG on a 20A circuit.

Smart Switch Installation Note

Most smart dimmers and smart switches require three things at the switch box:

1. A hot (line) wire
2. A load wire (switched hot to fixture)
3. A neutral wire

Power-to-switch wiring (Method 1) provides all three. A traditional switch loop (Method 2) does not provide a neutral, so smart switches requiring neutral cannot be installed without rewiring or using a no-neutral smart switch (which uses a tiny trickle current through the load for power -- only works with some fixture types and loads).

You can map out both wiring methods in CircuitDiagramMaker before starting your project -- trace the hot, neutral, and ground paths for each method to make sure you understand the circuit before you pick up a screwdriver.

Create Your Own Light Switch Wiring Diagram

CircuitDiagramMaker makes it straightforward to document residential wiring:

• Draw switch boxes, fixture boxes, and panel with accurate wire routing
• Color-code black, white, and bare ground conductors
• Show neutral pass-through in Method 1 and switch loop re-identification in Method 2
• Annotate wire gauges and breaker ratings
• Export as a PDF for permit applications or future reference

Create your own light switch wiring diagram -- free

Key Takeaways

• A single-pole switch interrupts the hot conductor only -- never switch the neutral.
• Power-to-switch (Method 1) brings power to the switch box first and provides a neutral at the switch -- required for new construction under 2011 NEC and needed for smart switches.
• Power-to-fixture with a switch loop (Method 2) is common in older homes; the white switch loop wire must be re-identified as hot with black tape at both ends.
• Always verify the circuit is dead with a non-contact voltage tester before touching any wires.
• Use 14 AWG on 15A circuits and 12 AWG on 20A circuits -- do not mix gauges on the same circuit.
• For control from two locations, use 3-way switches; single-pole switches control only one location.
• Ground all switches per NEC 404.9(B) -- bonding the switch to the grounded metal box satisfies this requirement if no dedicated ground wire reaches the box.

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Originally published at https://circuitdiagrammaker.app/blog/light-switch-wiring-diagram.