DPDT Switch Diagram: Complete Wiring Reference for Double Pole Double Throw Switches

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A DPDT switch diagram maps all six terminals of a double pole double throw switch and shows how to wire it for motor direction reversal, supply selection, and dual-circuit control applications.

DPDT stands for double pole double throw — a switch architecture with six terminals arranged as two independent poles, each pole having one common (C) terminal that connects to either of two throw positions (throw 1 / throw 2). Both poles are mechanically ganged, so a single actuation simultaneously switches both poles between the same throw positions. This ganged action is what makes the DPDT uniquely useful: two separate circuits can be routed or reconfigured simultaneously without requiring two separate actuations.

The six terminals are commonly labelled: C1 (common pole 1), T1a and T1b (throws for pole 1), C2 (common pole 2), T2a and T2b (throws for pole 2). In position A: C1 connects to T1a and C2 connects to T2a. In position B: C1 connects to T1b and C2 connects to T2b. At no point do the two poles connect to each other internally — they are electrically isolated from each other within the switch body.

The motor direction reversal circuit is the most widely referenced DPDT application and the one most clearly illustrating the switch's unique capability. The permanent-magnet DC motor is connected between C1 and C2. The positive supply rail connects to T1a and T2b. The negative supply rail connects to T1b and T2a (cross-connected). In position A, current flows: positive → T1a → C1 → motor → C2 → T2a → T2b → negative — establishing forward rotation. In position B, current flows: positive → T2b → C2 → motor (reversed) → C1 → T1b → negative — reversing rotation. The cross-connection is the key: the motor leads are always connected to the two COM terminals, and it is the supply polarity at those terminals that reverses.

For relay-type DPDTs (DPDT relays), the switch contacts described above are controlled by an electromagnetic coil rather than a manual actuator. The coil draws a small control current (typically 10–200 mA) to energise the relay, while the contacts switch much larger currents independently. This provides galvanic isolation between the control circuit and the load circuit, an important property in industrial and safety-critical applications.

DPDT switch packages exist as panel-mount toggles, slide switches, rocker switches, PCB-mount push buttons (momentary DPDT), and relay modules. Physical dimensions, terminal pitch, current rating, and AC versus DC ratings all vary by package — always verify the datasheet for the specific component before designing the circuit.

How to wire dpdt switch diagram

Confirm the switch is genuinely DPDT using a continuity tester With no circuit connected, use a multimeter in continuity mode. In position A, confirm C1-T1a continuity and C2-T2a continuity, and no continuity between C1-T1b or C2-T2b. In position B, confirm the opposite. Also confirm no continuity between any terminal of pole 1 and any terminal of pole 2.
Draw the circuit diagram for the intended application Sketch the complete circuit showing all six switch terminals and the connected supply and load. For motor reversal: label positive supply, negative supply, motor terminal A, and motor terminal B, and show exactly which switch terminal each connects to before beginning physical wiring.
Install the switch in the panel or enclosure Mount the switch in the panel cutout. For toggle switches, ensure the toggle lever travel is not obstructed by adjacent components or the enclosure door. Tighten the panel nut to the manufacturer's specified torque — overtightening cracks the switch body on plastic-bodied types.
Connect the load (motor, circuit) to the two COM terminals Connect the two leads of the motor (or circuit) to C1 and C2. Use correctly gauged wire with crimped terminals or appropriate insulated connectors. Verify wire gauge is adequate for the full load current.
Connect the supply to the throw terminals with cross-wiring for motor reversal For motor reversal: connect positive supply to T1a and T2b. Connect negative supply to T1b and T2a. This cross-connection is what achieves polarity reversal. Use colour-coded wire (red for positive, black for negative) and label T1b and T2a with a flag label indicating they are negative supply connections despite being connected on the 'positive side' of pole 1.
Test without load current, then test under load Verify switch action with a multimeter before connecting supply voltage. Then connect supply, operate the switch to position A, and confirm the motor turns in the expected direction. Toggle to position B and confirm reversal. Measure current in both positions to confirm the motor is drawing within its rated range.

Specifications

Terminal count	6 (2 COM, 2 NC throws, 2 NO throws)
Simultaneous poles switched	2 (mechanically ganged)
Positions	2 (ON-ON) or 3 for centre-off (ON-OFF-ON)
Typical PCB-mount toggle rating	250 V AC / 6 A; 125 V DC / 3 A
Typical industrial relay DPDT contact rating	250 V AC / 10 A; 30 V DC / 10 A
Mechanical life (typical toggle switch)	10 000–50 000 operations

Safety warnings

For mains AC applications, use only DPDT switches rated for the mains voltage (minimum 250 V AC) and load current. Working on mains wiring must comply with applicable wiring regulations (NEC/NFPA 70, BS 7671, IEC 60364, AS/NZS 3000) and must be performed by a licensed electrician.
Do not switch a motor using a DPDT while the motor is running at speed without first verifying the switch's inductive load rating and ensuring adequate arc suppression. High inductive currents during motor switching can cause severe contact arcing and switch failure.
In DC circuits above 30 V, arcing at the switch contacts during switching can be persistent and energetic. Use a switch rated for DC at the operating voltage, not the AC voltage — DC and AC ratings differ significantly.
Never short-circuit the supply by connecting both T1a and T2a to positive at the same time as T1b and T2b to negative — verify the cross-wiring layout carefully before energising.

Tools needed

Digital multimeter with continuity and resistance modes
Insulated screwdrivers
Wire strippers and crimping tool
Soldering iron (for PCB-mount DPDT switches)
Fuse holder and rated fuses
Clamp ammeter or series ammeter for current verification

Common mistakes

Not cross-wiring the supply connections to the throw terminals — wiring positive to T1a and T2a (same side, not cross-connected) will not reverse the motor polarity regardless of switch position.
Connecting the motor between C1 and T1a of the same pole, rather than between C1 and C2 across both poles.
Using an AC-rated switch in a DC circuit above the switch's DC voltage rating, causing excessive arcing and premature contact failure.
Failing to use a centre-off (ON-OFF-ON) switch where the application requires the motor to be positively off between forward and reverse positions.
Selecting a switch by physical size or price without verifying the current and voltage ratings against the circuit requirements.

Troubleshooting

Motor runs in the same direction in both switch positions: Cause: Supply connections to the throw terminals are not cross-wired — both positive connections are on the same side (T1a and T2a) and both negative on the other side (T1b and T2b). Fix: Isolate the circuit. Swap either the T2a and T2b connections, or the T1a and T1b connections, to achieve the correct cross-wired layout. Verify with continuity test before re-energising.
No motor movement in either switch position: Cause: Motor connected to C1 and T1a (same pole) instead of C1 and C2 (across both poles), or open-circuit fuse. Fix: Check fuse condition. Verify motor terminals connect to C1 and C2. Measure voltage across C1 and C2 in each switch position — correct wiring should show supply voltage with reversed polarity between the two positions.
Switch contacts burn or pit rapidly: Cause: Motor inrush or inductive switching current exceeds the switch's rated contact capacity, causing excessive arcing on every operation. Fix: Measure motor stall current and verify the switch rating exceeds this. Replace with a higher-rated switch, or add an RC snubber across the switch contacts to suppress arcing. For larger motors, use the DPDT to control a relay or contactor whose contacts are rated for the motor current.

Frequently asked questions

What does DPDT mean?

DPDT means double pole double throw. 'Double pole' means the switch simultaneously controls two independent electrical circuits (two poles). 'Double throw' means each pole can connect its common terminal to one of two possible throw terminals. The result is a six-terminal switch that can route two circuits to two different destinations simultaneously.

How many terminals does a DPDT switch have?

A DPDT switch has exactly six terminals: two common terminals (one per pole) and four throw terminals (two per pole — one normally-open throw and one normally-closed throw for each common). Always verify with a continuity check because some component labels are incorrect or ambiguous on low-cost switches.

Can a DPDT switch be used as a SPDT switch?

Yes. Connect only one pole (C1, T1a, T1b) and leave the second pole (C2, T2a, T2b) unconnected. The switch will operate as a standard SPDT switch using the connected pole. This is a valid approach when only single-pole switching is required but a DPDT is the only switch available.

What is the difference between a DPDT switch and an H-bridge motor driver?

A manual DPDT switch achieves motor reversal mechanically — the operator physically toggles the switch. An H-bridge motor driver achieves the same result electronically using four transistors, allowing automated forward/reverse control from a microcontroller signal. An H-bridge also allows pulse-width modulation (PWM) for speed control, which a manual DPDT switch does not provide.

Is a DPDT relay the same as a DPDT switch?

Functionally the switch contacts behave identically to a manual DPDT switch in either position. The difference is the actuation method: a DPDT relay uses an electromagnetic coil energised by a control signal to move the switch contacts, providing electrical isolation between the control circuit and the switched circuit. A manual DPDT is actuated by hand.