An SPDT switch is a single pole, double throw device with one common terminal and two throws. In each stable position of a conventional two-position changeover switch, the circuit is redirected from one throw to the other rather than left open. Catalogues write the same configuration as 1P2T, changeover, or COM/NO/NC depending on region and product line. The code carries no information about momentary action, terminal numbering, rating or shorting behaviour. Swiclick builds this arrangement in selected G series micro switches, which use a snap-action mechanism with a changeover contact providing COM, NO and NC terminals, and across the MSK, SK and SS slide switch series in through hole and surface mount. Published micro switch ratings in this configuration run up to 16A at 125/250VAC, depending on part number. Contact form and terminal numbering vary by part number, so the contact diagram matters more than the abbreviation.
What the Three Terminals Do
Three terminals, three jobs, and only one of them is fixed.
The common terminal, usually marked COM or C, is the one your signal or supply enters through. In each stable position of a conventional two-position maintained switch, COM is connected to one throw. It may be open during a break-before-make transition, during contact bounce, or in a centre-off position on variants that have one.
The two throws are the destinations. In a micro switch they are usually marked NO and NC, meaning normally open and normally closed, where normally describes the unactuated state rather than the powered state. In a slide switch they are more often just numbered.
Which throw sits closed at rest is a property of the part, not of the abbreviation. A part described as SPDT tells you there are two destinations. It does not tell you which one the switch rests on.
The Same Configuration Under Several Names
Buyers reading across suppliers meet the same arrangement written four ways.
SPDT is the Western convention, from single pole double throw. 1P2T is the same thing written as one pole, two throws, and it appears throughout Asian catalogues including parts of the Swiclick range. Changeover is the European term, sometimes abbreviated CO. COM/NO/NC describes the terminals rather than the topology and is standard in micro switch and relay work.
None of these is more correct than the others. The pole and throw notation is consistent enough that a drawing will translate, but the terminal numbering will not. Two suppliers can both call a part SPDT and number the pins in opposite order.
Verify against the contact diagram before you commit a footprint.
Across the Product Families
The same configuration behaves differently depending on which mechanism carries it.
Micro switches (G series). Selected G series parts use a snap-action mechanism with a changeover contact, giving COM, NO and NC terminals. SPST-NO variants also exist in the same series and do not expose all three. Terminals come as solder pin, PCB mount, quick-connect and 90-degree bend foot. An SPDT PCB micro switch in the G15 series is one example where the switch sits on the board.
Slide switches (MSK, SK, SS). Three-terminal bodies with the common in the middle on most conventional layouts. Lower switching ratings than the micro bodies because contact transfer depends more on actuator movement. The SPDT slide switch page covers the format in detail.
Tact switches. No tact switch product name reviewed in July 2026 explicitly stated an SPDT or changeover configuration. Because many product names do not state their contact configuration, confirm availability with Swiclick before treating this as a complete configuration audit. If a finger presses a button and the circuit needs two destinations, the answer is usually a micro switch rather than a tactile one.
Manufacturer-specific note: ratings, contact forms and terminal layouts quoted on this page apply only to the identified Swiclick models and must be verified against the exact datasheet.
Wiring It as an On and Off Switch
An SPDT part wired to two of its three terminals behaves as a simple SPST switch. Use the common and one throw, and leave the third terminal unconnected.
This is a normal thing to do. In some series the changeover version is the higher-volume part and may quote similarly to or below the two-terminal variant, so compare both part numbers at RFQ. It is worth keeping the unused pad on the board so a later revision can pick up the second throw without a layout change.
The reverse is not possible. A two-terminal SPST part cannot be made into a changeover, so if there is any chance a future revision needs a second destination, buy the third terminal now.
What the Abbreviation Does Not Tell You
Four specifications sit outside the configuration code and get left off RFQs.
Momentary or maintained. Whether the switch returns when released. This is independent of poles and throws.
Shorting or non-shorting. Whether the common touches both throws briefly during transition. It matters when the two throws are separate supplies.
Ratings and load type. Requirements and rating rules for mechanical switches of this class sit in IEC 61058-1-1. The configuration code carries no rating information at all.
Terminal numbering. Discussed above, and the most common cause of a mirrored assembly.
Choosing between SPDT and DPDT is a separate decision that depends on whether a second circuit has to move at the same time.
Specifying One
- Poles and throws, plus which throw is closed at rest
- Momentary or maintained
- Shorting or non-shorting, if the two throws are separate sources
- Load type, current and voltage, including whether it is DC
- Terminal style, orientation and mounting method
- Ambient temperature range and required certifications with destination market
- Annual volume
Selected Swiclick part numbers in this configuration may be covered by UL, TÜV Rheinland or ENEC files. Approval is granted per model, rating and construction, so confirm the exact part against the current certificate before writing it into a compliance document.
FAQ
Single pole double throw. One circuit, two possible destinations, three terminals in the usual package.
Yes, they describe the same configuration. 1P2T is common in Asian catalogues and SPDT in Western ones. Terminal numbering still has to be read from the specific datasheet.
On most conventional three-terminal bodies it is the middle one, and on micro switches it is usually marked COM. Confirm against the contact diagram rather than assuming.
In a stable position on a conventional two-position part, no. It can be open during a break-before-make transition, during contact bounce, or in a centre-off position on variants built with one.
Yes. Wire the common and one throw and leave the third terminal open. Keep the pad on the board for future use.
No. Momentary and maintained action is a separate specification from poles and throws, and both exist in SPDT form.
