A double rocker switch (technically a duplex stacked Decora switch, like the Leviton 5643-W) allows you to control two independent 120V loads from a single-gang electrical box. This is the standard solution for bathroom vanity lights and exhaust fans, or kitchen under-cabinet lighting pairs. The direct answer to the most common bench question: the top two brass terminals control the top rocker, the bottom two brass terminals control the bottom rocker, and the green terminal is ground. There are no silver (neutral) terminals on a standard 120V double rocker because the switch only breaks the ungrounded (hot) conductor.

⚠ Mains Voltage Safety Warning: This procedure involves 120V AC mains wiring. De-energize the circuit at the breaker panel, apply a lockout/tagout device per OSHA hazardous energy standards, and verify the wires are dead with a non-contact voltage tester before touching any terminals.

Terminal Mapping and Diagram Symbols

Before stripping wires, you need to understand the physical layout of the device. A duplex rocker is essentially two Single-Pole Single-Throw (SPST) switches sharing one plastic strap and one ground screw. In wiring diagrams, you will see two distinct SPST symbols stacked vertically. The 'Line' side is where power enters from the panel; the 'Load' side is where power exits to the fixture.

Physical Terminal Diagram Symbol Wire Color (US NEC) Multimeter Continuity Test
Top Rocker Line (Brass) SPST-1 Input (Left side) Black (or Red) Hot 0 Ω to Top Load when ON; OL when OFF
Top Rocker Load (Brass) SPST-1 Output (Right side) Black (Switched Hot) 0 Ω to Top Line when ON; OL when OFF
Bottom Rocker Line (Brass) SPST-2 Input (Left side) Black (or Red) Hot 0 Ω to Bottom Load when ON; OL when OFF
Bottom Rocker Load (Brass) SPST-2 Output (Right side) Red or Black (Switched Hot) 0 Ω to Bottom Line when ON; OL when OFF
Ground (Green) Earth Ground Symbol Bare Copper or Green Always 0 Ω to metal wall box / panel ground

Understanding the Breaking Fin: On the 'Line' side of most duplex rockers, the two brass screws are connected by a small metal tab (the breaking fin). If you are feeding both rockers from the exact same 15A or 20A breaker, you leave this fin intact and land your single hot wire on either Line screw. If you are feeding the top and bottom rockers from two separate breakers, you must use needle-nose pliers to snap this fin off, isolating the two circuits.

Node-by-Node Current Trace (Source to Load)

To read a double rocker switch wiring diagram correctly, you must trace the current path node-by-node. Below is the exact trace for a standard bathroom setup: Top Rocker controls the vanity light, Bottom Rocker controls the exhaust fan. Both are fed from a single 15A, 120V AFCI/GFCI breaker.

Trace 1: Top Rocker (Vanity Light)

  1. Panel Breaker (15A): 120V AC (nominal 114V-126V) exits the breaker on a 14 AWG black hot wire.
  2. Wall Box Entry: The black hot wire enters the single-gang box and lands on the Top Rocker Line brass terminal.
  3. Internal Contacts: When the top rocker is pressed ON, the internal brass wiper bridges the Line and Load contacts.
  4. Switched Hot Exit: Current exits the Top Rocker Load brass terminal onto a 14 AWG black (or red) switched-hot wire.
  5. Fixture (Vanity): The switched-hot wire connects to the black lead on the vanity light fixture.
  6. Neutral Return: Current flows through the fixture and returns via the fixture's white neutral wire, which is wire-nutted directly to the panel's 14 AWG white neutral wire in the back of the box. (The neutral never touches the switch).

Trace 2: Bottom Rocker (Exhaust Fan)

  1. Shared Feed: Because the breaking fin is intact, the same 120V source feeds the Bottom Rocker Line brass terminal.
  2. Internal Contacts: Pressing the bottom rocker ON bridges the bottom Line and Load contacts.
  3. Switched Hot Exit: Current exits the Bottom Rocker Load terminal onto a 14 AWG red switched-hot wire.
  4. Fixture (Fan): The red wire connects to the fan motor's hot lead, returning via the shared neutral bundle.
ⓘ Polarity and Ground Path Callout: NEC Article 404 strictly requires that switches only break the ungrounded (hot) conductor. Never wire a switch to break the neutral. The ground path is entirely separate from the switching mechanism: the bare copper ground wire from the panel connects to the metal wall box (via a 10-32 green ground screw) and pigtails to the green ground screw on the double rocker switch strap. This ensures the plastic Decora faceplate and switch strap remain at 0V potential during a fault.

Installation Steps and Meter Verification

Follow this sequence to wire the device and mathematically verify your work before energizing the panel.

  1. De-energize and Verify: Turn off the breaker. Test the existing wires with a Non-Contact Voltage Tester (NCVT). Follow up with a Digital Multimeter (DMM) set to VAC, measuring between the black hot and the bare ground. It must read 0.0V.
  2. Prepare the Wires: Strip 3/4 inch of insulation from your 14 AWG THHN or NM-B wires. Use a wire gauge hole on your strippers to avoid nicking the copper, which creates a hot spot.
  3. Establish the Ground: Connect the bare copper ground to the green screw on the switch. Torque to roughly 14 in-lbs (snug, but do not strip the soft brass threads).
  4. Land the Neutrals: Wire-nut the incoming white neutral, the vanity white neutral, and the fan white neutral together using a yellow or red winged wire nut. Push this bundle deep into the back of the box.
  5. Connect the Line (Hot): Land the incoming black hot wire on one of the Line-side brass screws. Ensure the breaking fin is intact if sharing the feed.
  6. Connect the Loads: Land the vanity switched-hot on the Top Load brass screw, and the fan switched-hot on the Bottom Load brass screw. Use the side-wiring saddle or the back-wire clamps (if your model has them), avoiding the old 'push-in' stab holes which degrade over time.
  7. Pre-Power Continuity Test: Set your DMM to Continuity/Ohms (Ω). Place probes on the Top Line and Top Load screws. Toggle the top rocker. You should see OL (Open Loop) when OFF, and <1 Ω when ON. Repeat for the bottom rocker.
  8. Energize and Voltage Test: Turn the breaker on. Set DMM to VAC. Measure between the Top Load screw and the ground box. It should read 0V when OFF, and ~120V when ON. Repeat for the bottom load.

Common Wiring Mistakes and Box Fill Violations

When working with double rocker switch diagrams, DIYers frequently run into physical and electrical constraints that aren't obvious until the drywall is cut.

Mistake Consequence The Fix
Leaving the breaking fin intact on a Multi-Wire Branch Circuit (MWBC) Dead short between two 120V legs (240V across the fin), tripping both breakers instantly and potentially welding the contacts. Snap the fin off with pliers. Ensure the two hot wires are on opposite legs (240V between them) and share a single neutral.
Exceeding NEC 314.16 Box Fill limits A single-gang box with a duplex switch, 2 loads, and a neutral bundle requires massive volume. Wires get crushed, damaging insulation. Use an extra-deep single-gang box (minimum 22.5 cubic inches for 14 AWG with a duplex device). Calculate 2 cu in per wire, 4 cu in for the duplex device.
Using back-stab push-in terminals The internal spring clips loosen over time due to thermal expansion/contraction, causing arcing and flickering lights. Always use the side-binding screw terminals or the screw-clamp plate terminals. Bend a proper J-hook in the wire.

For complete code compliance regarding switch placement and box fill calculations, always refer to the latest edition of NFPA 70 (National Electrical Code), specifically Articles 314 and 404. Remember that local Authority Having Jurisdiction (AHJ) inspectors have the final say on whether a specific stacked device installation passes inspection in your municipality.