A Double Pole Double Throw (DPDT) switch controls two separate circuits simultaneously, routing each between two distinct paths. Physically, it contains six terminals: two common inputs (or outputs) and four throws. If you are wiring a 120V AC workshop circuit, the direct answer for your terminal mapping is: the center row is your Common (source/load), the top row is Throw 1, and the bottom row is Throw 2. Never switch the neutral or ground through the toggle mechanism.

MAINS VOLTAGE WARNING: This guide assumes a 15A, 120V AC branch circuit. Before touching any conductors, turn off the breaker, lock out the panel if possible, and verify the circuit is dead using a non-contact voltage tester and a multimeter. Local NEC-style guidance requires switching only the ungrounded (hot) conductor. Your local Authority Having Jurisdiction (AHJ) has final authority on code compliance.

Decoding the Diagram Symbols and Terminal Map

On a schematic, the DPDT switch symbol looks like two Single Pole Double Throw (SPDT) switches drawn side-by-side, linked by a dashed mechanical line. That dashed line is critical: it tells you that moving the physical actuator shifts both internal wipers at the exact same time.

Physical toggle switches rarely have "L1" or "T1" printed on the plastic housing. Instead, they rely on spatial positioning. Below is the exact terminal mapping for a standard 6-terminal heavy-duty toggle like the Hubbell HBL1286.

Physical Location Left Pole (Pole 1) Right Pole (Pole 2) Schematic Symbol Equivalent
Top Row Terminal 1 (Throw A1) Terminal 4 (Throw A2) Normally Open (NO) / Path 1
Center Row Terminal 2 (Common 1) Terminal 5 (Common 2) Wiper / Common (COM)
Bottom Row Terminal 3 (Throw B1) Terminal 6 (Throw B2) Normally Closed (NC) / Path 2
Bench Tip: If you are holding the switch with the toggle lever pointing UP, the internal wipers (Center Row) are physically touching the Top Row terminals. Lever DOWN connects Center to Bottom.

Node-by-Node Trace: Source to Load

To wire this correctly, you must trace the current path from the panel to the load, explicitly separating the switched hots from the continuous neutral and ground paths. Here is the exact node-by-node trace for switching two separate 120V loads from a single source.

  1. Panel to Switch Box: A 15A breaker feeds a 14/2 NM-B cable (or two 14 AWG THHN hots in conduit) into the switch box. The black hot wire lands on Terminal 2 (Common 1).
  2. Internal Jumper: A 4-inch pigtail of 14 AWG black wire jumps from Terminal 2 to Terminal 5 (Common 2). Both poles now share the same line-side voltage.
  3. Switch to Load A: A 14 AWG black wire runs from Terminal 1 (Top Left) to the hot terminal of Load A (e.g., a dust collector).
  4. Switch to Load B: A 14 AWG black wire runs from Terminal 3 (Bottom Left) to the hot terminal of Load B (e.g., an air compressor).
  5. The Neutral Path (Bypass): The white neutral wire from the panel does not touch the switch. It is wire-nutted directly to the white neutral pigtails of both Load A and Load B inside the back of the box.
  6. The Ground Path (Bypass): The bare/green equipment grounding conductor (EGC) bypasses the switch entirely. It lands on the green ground screw inside the metal switch box, and a pigtail continues to bond the metal switch yoke and the downstream load enclosures. Never route the EGC through the switch terminals.

Decision Tree: Pick Your DPDT Configuration

A DPDT switch is highly versatile, but the wiring topology changes entirely based on your goal. Use this decision matrix to determine your wiring layout and select the correct hardware.

If Your Goal Is... Wire Sources To... Wire Loads To... Special Wiring Notes
Dual Load Switching (One source, choose between two devices) Center Row (Commons) Top & Bottom Rows Requires internal jumper between the two Center terminals.
Dual Source Switching (One device, choose between Grid vs. Inverter) Top & Bottom Rows Center Row (Commons) Do NOT jumper the sources together. Center terminals jumper to the single load.
DC Motor Reversing (Polarity swap for forward/reverse) Center Row (DC +/-) Top & Bottom Rows (Motor leads) Requires an "X" cross-wire pattern between the top and bottom throws to reverse polarity.

The Concrete Pick: For 120V/277V AC home and workshop applications (Dual Load or Dual Source), buy the Hubbell HBL1286 (15A, Heavy-Duty DPDT Toggle, approx. $38-$45). It features high-abuse thermoplastic housing and robust side-wire clamps that accept up to 12 AWG wire. If you are doing 12V/24V DC motor reversing, bypass the AC toggles and buy a Bodine 300-series DPDT toggle rated specifically for DC inductive loads, as AC switches will arc and weld shut when breaking DC current.

Step-by-Step Installation and Torque Specs

Assuming you are installing the Hubbell HBL1286 for a standard 15A AC dual-load circuit, follow these physical installation steps.

  1. Strip the Conductors: Strip exactly 3/4 inch of insulation from your 14 AWG THHN or solid copper wires. Do not nick the copper.
  2. Form the Jumper: Create your Center-to-Center jumper using a piece of 14 AWG solid black wire. Strip both ends to 3/4 inch.
  3. Terminate the Commons: Insert the main hot wire and one end of the jumper into the side-clamp plates of Terminal 2 and Terminal 5. Ensure no bare copper is exposed outside the clamp, and no insulation is trapped inside.
  4. Terminate the Throws: Land your Load A hot on Terminal 1 and Load B hot on Terminal 3. (Leave 4 and 6 empty if you only need one throw per pole, or use them if wiring a dual-source setup).
  5. Torque the Screws: Tighten the terminal screws to 14 in-lbs (1.6 Nm). If you lack a micro-torque screwdriver, tighten until the screw is snug, then give it an additional quarter-turn. Undertorquing causes high-resistance arcing; overtorquing strips the brass threads.
  6. Dress the Box: Fold the wires in a Z-pattern. Hots in the back, neutrals in the middle, grounds pushed to the very back of the metal box. Secure the switch yoke with the provided 6-32 machine screws.

Pre-Energization Verification with a Multimeter

Never throw the breaker without verifying the internal switching logic. Grab a multimeter (like a Fluke 117 or equivalent) and set it to Continuity mode (the diode/soundwave symbol).

  1. Verify Isolation: With the switch in the UP position, place one probe on Terminal 1 (Top Left) and the other on Terminal 3 (Bottom Left). The meter must read "OL" (Open Loop). If it beeps, you have a short circuit.
  2. Test Throw 1 (Up): Place probes on Terminal 2 (Center Left) and Terminal 1 (Top Left). The meter should beep (read < 1 ohm). Move the right probe to Terminal 3 (Bottom Left); it must read OL.
  3. Test Throw 2 (Down): Flip the toggle DOWN. Place probes on Terminal 2 and Terminal 3. The meter should beep. Move the right probe to Terminal 1; it must read OL.
  4. Repeat for Pole 2: Perform the exact same continuity checks on Terminals 4, 5, and 6 to ensure the right side of the switch is tracking mechanically with the left side.
  5. Ground Bond Check: Place one probe on the metal switch yoke and the other on the bare ground wire pigtail. The meter must beep, confirming the yoke is bonded to the equipment grounding conductor.

Once all continuity tests pass, and you have confirmed the neutrals and grounds are wire-nutted securely outside the switch terminals, you can safely re-energize the 15A breaker. For further reading on switch enclosure and mounting requirements, consult NFPA 70 (NEC) Article 404 regarding snap switches and box fill calculations.