DPDT Switch Symbol

The DPDT Switch symbol (IEC 60617 / ANSI Y32.2).

Definition: The DPDT Switch symbol represents a double-pole, double-throw switch — two electrically independent SPDT changeover contacts operated by one actuator — drawn per IEC 60617 as two stacked single-pole changeover contacts joined by a dashed mechanical-link line, with six terminals: In 1 and In 2 (the poles/commons) and Out 1A/1B and Out 2A/2B (the throws).

Also known as: DPDT switch, double-pole double-throw switch, DPDT toggle, polarity-reversing switch, 2P2T switch, changeover switch (2-pole), ON-ON switch.

What the DPDT Switch symbol means

The DPDT symbol denotes one mechanical action switching two separate circuits simultaneously, each between two alternative paths. 'Double pole' means two independent commons (In 1, In 2) that never touch each other inside the switch; 'double throw' means each common connects to one of two outputs (A or B) depending on lever position. The dashed line linking the two contact arms is essential grammar: it says the poles are mechanically ganged — they always move together — while remaining electrically isolated.

The DPDT's celebrity application is polarity reversal: cross-wire the two B throws to the opposite A throws and a DC motor connected to the commons runs forward in one lever position and backward in the other — the mechanical ancestor of the H-bridge. Beyond that, DPDT switches route stereo audio (both channels at once), transfer a load between two sources, select between two instruments sharing one output, and implement true two-circuit isolation switching that a single-pole switch cannot.

How to identify the DPDT Switch symbol

Look for two SPDT contact symbols — each a pivoting arm (pole) that can rest on either of two contact dots (throws) — drawn one above the other, with a dashed vertical line tying the two arms together. The dashed line is the identifier: solid lines are conductors, dashed lines are mechanical linkage carrying no current. Six terminals total confirms DPDT; four terminals with ganged arms and single throws would be DPST, and three terminals a lone SPDT.

IEC 60617 and ANSI Y32.2 / IEEE 315 draw the contacts almost identically for this device; ANSI toggle-switch forms sometimes show the throws as small circles and the IEC form as bare line ends, and centre-off (ON-OFF-ON) variants add a middle rest position. On physical switches the six solder lugs are arranged in two columns of three, with the commons in the middle row — matching the symbol's geometry.

Function in a circuit

Each pole works as an independent changeover: In 1 connects to Out 1A or Out 1B, never both (in a standard break-before-make switch), while In 2 simultaneously connects to Out 2A or Out 2B. This lets one flick of a lever redirect two conductors at once — both legs of a DC supply, both channels of a stereo pair, or a signal plus its ground/return. Because the two poles are isolated, they can even carry unrelated circuits: one pole switching a 12 V motor while the other switches a 5 V indicator LED.

In the reversing configuration, the motor (or other polarised load) connects across In 1 and In 2; supply positive feeds Out 1A and Out 2B, supply negative feeds Out 1B and Out 2A (the familiar 'X' cross-wiring on the switch lugs). Position 1 delivers +/− to the motor, position 2 delivers −/+, reversing rotation. An ON-OFF-ON centre-off variant adds a stop position, forming a complete forward-off-reverse motor controller from one component.

Standards: IEC vs ANSI

IEC 60617	IEC 60617 builds the DPDT from two single-pole changeover contact symbols with the dashed mechanical-coupling line defined in the standard's general contact rules; IEC 61058-1 governs switch performance for appliances and IEC 60947-3 for industrial switching devices.
ANSI/IEEE 315	ANSI Y32.2 / IEEE 315 defines the equivalent double-pole double-throw form with ganged SPDT contacts; UL 61058-1 (harmonised) and legacy UL 1054 cover North American component-switch safety ratings.
Key difference	The drawn forms are near-identical; both rely on the dashed line for mechanical ganging. Terminology differs more than the drawing: IEC literature says 'two-pole changeover switch' where North American catalogues say 'DPDT'; toggle-position nomenclature (ON-ON, ON-OFF-ON, (ON)-OFF-(ON) with parentheses meaning momentary) is a North American catalogue convention now used globally.

Terminals / pins

Pin	Name
in1	In 1
out1a	Out 1A
out1b	Out 1B
in2	In 2
out2a	Out 2A
out2b	Out 2B

Typical values

Common miniature DPDT toggles and slide switches are rated 5–6 A at 125 V AC / 3 A at 250 V AC, with DC ratings much lower (typically 20–28 V DC at rated current) because DC arcs don't self-extinguish; sub-miniature PCB types run 0.5–3 A. Contact resistance is specified ≤10–50 mΩ; mechanical life 25,000–100,000 operations; electrical life 6,000–25,000 at full load. Standard variants: ON-ON, ON-OFF-ON (centre off), momentary (ON)-OFF-(ON); heavy-duty DPDT rockers and knife switches reach 15–30 A for battery and PV changeover duty.

Where the DPDT Switch symbol is used

DC motor direction (forward/reverse) control via cross-wired polarity reversal in toys, hoists, trolling motors and model railways
Guitar and audio gear: pickup phase switches, series/parallel switching, stereo channel routing and effects loop true-bypass (as part of 3PDT variants)
Source transfer: switching a load between two supplies, e.g. battery bank A/B or mains/inverter changeover at small scale
Instrumentation and test rigs routing a signal pair to either of two instruments or fixtures
Railway/model layout point (turnout) control and frog polarity switching
Centre-off DPDT variants as complete forward-off-reverse controllers for linear actuators, blinds and antenna rotators

Example

In a motor-reversing circuit, the DC motor's two leads connect to the switch commons In 1 and In 2; the 12 V supply positive feeds Out 1A and is cross-jumpered to Out 2B, while supply negative feeds Out 2A and cross-jumpers to Out 1B — flip the lever one way and In 1 = +12 V / In 2 = 0 V spinning the motor forward, flip it the other way and In 1 = 0 V / In 2 = +12 V reversing it; choosing an ON-OFF-ON version adds a stop position in the middle.

Key facts

DPDT = double pole (two isolated commons: In 1, In 2), double throw (each common selects Out A or Out B) — six terminals, one actuator.
The dashed line between the two contact arms is mechanical linkage, not a conductor: the poles move together but are electrically independent.
Cross-wiring the outputs (1A↔2B jumpered, 1B↔2A jumpered) turns a DPDT into a polarity-reversing switch — the classic DC motor forward/reverse circuit.
Toggle nomenclature: ON-ON (two positions), ON-OFF-ON (centre off), parentheses as in (ON)-OFF-(ON) denote momentary positions.
Standard switches are break-before-make: the common leaves one throw before reaching the other, so the two outputs are never bridged.
DC ratings are far below AC ratings for the same switch — a 6 A/250 V AC toggle is often only rated ~20–28 V DC because DC arcs don't self-quench at current zero-crossings.
On the physical six-lug package the commons are the centre row, matching the symbol; the relay equivalent of a DPDT is a two-changeover (2 Form C) relay.
Two poles may switch completely unrelated circuits at different voltages simultaneously — e.g. a load and its status LED.

Frequently asked questions

How do you wire a DPDT switch to reverse a DC motor?

Connect the motor across the two commons (In 1, In 2 — the centre lugs). Feed supply positive to Out 1A and supply negative to Out 2A, then add two crossing jumpers: Out 1A to Out 2B and Out 2A to Out 1B. Now one lever position applies +/− to the motor and the other applies −/+, reversing rotation. Use an ON-OFF-ON (centre-off) DPDT if you also want a stop position, and never flip direction at full speed on large motors — the reversing inrush is severe.

What is the difference between DPDT and DPST?

Both have two ganged poles, but DPST (double pole, single throw) is just two ON/OFF contacts — four terminals — that make or break two conductors together, like switching line and neutral simultaneously. DPDT adds a second throw per pole — six terminals — so each pole selects between two destinations rather than merely opening. Any DPDT can be used as a DPST by ignoring one pair of throws, but not vice versa.

What does the dashed line in the DPDT symbol mean?

It represents the mechanical link — the shared actuator bar — that forces both contact arms to move at the same instant. It carries no current and is deliberately drawn dashed to distinguish mechanical coupling from electrical conductors. This convention comes from IEC 60617's general rules and appears identically in relay symbols, where a coil's dashed line gangs multiple contact sets.

What do ON-ON, ON-OFF-ON and (ON)-OFF-(ON) mean on a DPDT toggle?

They describe the lever positions. ON-ON: two positions, each connecting the commons to one throw set — no off state. ON-OFF-ON: three positions with a centre off where the commons touch nothing — ideal for forward/off/reverse. Parentheses mean momentary (spring-return): (ON)-OFF-(ON) returns to centre when released, suiting jog controls. The contact arrangement is identical DPDT in all cases; only the detent/spring mechanics differ.

Can I switch mains with a DPDT toggle rated 6 A 250 V AC?

Electrically yes, within its AC rating — a DPDT is actually good practice for isolating both line and neutral together (using it as a double-pole disconnect). But observe three cautions: use the AC rating, not for DC at that voltage (DC ratings are typically only 20–28 V); ensure the switch carries the relevant safety approval (UL/ENEC to IEC 61058-1); and enclose it so no terminals are touchable. For inductive loads (motors, transformers) derate — many toggles specify roughly half the resistive current for inductive duty.

Related symbols

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