2026-09-11 The four common toggle switch contact arrangements are SPST, SPDT, DPST and DPDT. SPST switches one circuit on or off; SPDT selects between two paths; DPST switches two separate circuits on or off together; and DPDT changes over two separate circuits with one lever.
But those abbreviations do not tell you everything. Two switches with the same number of terminals may behave differently: one stays where you leave it, another springs back, and a third includes a center-off position. Before ordering a replacement, match the contact arrangement, operating action, electrical ratings and mounting details.
Toggle switch types at a glance
A pole is an independently switched circuit. A throw is a contact path that each pole can select. The lever can operate more than one pole mechanically without connecting those circuits electrically.
| Type | Full name | Typical contact terminals | Basic function |
|---|---|---|---|
| SPST | Single pole, single throw | 2 | Open or close one circuit. |
| SPDT | Single pole, double throw | 3 | Connect one common terminal to either of two contacts. |
| DPST | Double pole, single throw | 4 | Open or close two separate circuits together. |
| DPDT | Double pole, double throw | 6 | Change over two separate circuits together. |
These terminal counts apply to basic, non-illuminated contact arrangements. Lamps, duplicated terminals and other construction details can change the total. Terminal count is a useful clue, not proof of the switch function. For more on the terminology, see TE Connectivity’s explanation of switch poles and throws.
Contact diagrams: what connects in each position?
The simplified diagrams below show electrical continuity, not physical pin locations. A solid line means connected; a gap means open. Letters are reference labels for this guide, not manufacturer terminal numbers. Lever direction and terminal orientation must be checked against the exact switch drawing.
SPST: one circuit on or off
OFF: A o o B ON: A o-----o B
SPST is appropriate when the required function is simply connected or disconnected. It does not select a second path. Whether it can switch a particular load depends on its rating, not the size of its lever.
SPDT: one common, two selectable paths
Position A: C o-----o A B open Position B: C o-----o B A open Center OFF*: C disconnected from A and B *Only on a center-off version.
An SPDT ON-ON switch selects one path or the other. An SPDT ON-OFF-ON switch adds a center position in which neither path is connected. Buying an ON-ON version when the circuit needs center OFF changes the way the equipment operates.
DPST: two separate on/off circuits
OFF: A1 o o B1
A2 o o B2
ON: A1 o-----o B1
A2 o-----o B2
Both contact sets operate from the same lever, but they remain separate electrical paths. DPST does not provide the alternative connections available from DPDT.
DPDT: two changeover circuits
Position A: C1 o-----o A1 B1 open
C2 o-----o A2 B2 open
Position B: C1 o-----o B1 A1 open
C2 o-----o B2 A2 open
Center OFF*: Both commons disconnected
from their selectable contacts.
*Only on a center-off version.
Think of DPDT as two SPDT contact sets operated by one actuator. These diagrams show the settled positions only; they do not specify what happens during the transition. If switching sequence matters, check whether the manufacturer specifies break-before-make or another contact sequence.
ON-ON, ON-OFF-ON and momentary operation
Contact arrangement and operating action answer different questions. SPDT tells you which paths are available. ON-OFF-ON tells you the position functions. Momentary or maintained tells you what happens when you release the lever.
| Common notation | Position functions | Typical release behavior |
|---|---|---|
| ON-OFF | Connected / disconnected | Maintained when specified without momentary action. |
| ON-ON | Path A / path B; no center OFF | Stays in the selected position. |
| ON-OFF-ON | Path A / disconnected / path B | Maintained positions unless otherwise specified. |
| (ON)-OFF-(ON) | Momentary path A / OFF / momentary path B | Returns to center OFF from either side. |
Parentheses commonly indicate momentary action, but manufacturers may use other notation, including MOM. In a three-column function table, NONE can mean that no center position exists; it is not the same as OFF. The C&K T Series datasheet provides examples of these function tables and their associated terminal connections.
Does a 3-pin or 6-pin switch identify the wiring?
Not by itself. A simple three-terminal switch may be SPDT, but an illuminated on/off switch can also have three terminals because its lamp needs a separate connection. Similarly, six terminals suggest a common DPDT arrangement without proving the terminal assignment.
Start with the manufacturer name, part number and contact drawing. Check whether the drawing shows a terminal-side or actuator-side view. Do not assume the center terminal is common, or that moving the lever toward a terminal connects that terminal.
For an unpowered, electrically isolated plain mechanical switch, a continuity check can help confirm which terminals connect in each position. Disconnect all power and isolate the switch from other circuit paths first; never use continuity mode on an energized circuit. A meter check does not establish voltage rating, load suitability or safe use with mains power.
Choosing between similar-looking replacements
Once the function is right, compare the specifications that determine whether the replacement will work in the actual assembly:
- Electrical load: match the manufacturer’s AC or DC rating at the required voltage. Do not assume an AC rating applies to DC, or that a resistive-load rating covers motor inrush and other demanding loads.
- Signal level: for a low-level control input, check the contact material and any minimum-load requirements. A higher current rating is not automatically better for a small signal.
- Mechanical fit: check the panel cutout, bushing thread, permitted panel thickness, lever length and clearance behind the panel. For PCB mounting, compare the complete footprint and orientation.
- Operating environment: verify the required temperature range and sealing conditions. A terminal seal for assembly cleaning does not automatically make the installed panel waterproof.
Keep the two poles of a double-pole switch within their specified use. Do not parallel them to claim twice the current rating unless the manufacturer explicitly permits that arrangement.
A specific example: TMS3T5B2M6RE
TE Connectivity identifies TMS3T5B2M6RE under part number 2267078-6. Its SPDT, ON-OFF-ON function illustrates why “three-position toggle switch” is not a complete ordering description: the full part number identifies the particular component, not just its broad function.
Use the TE product information and linked drawing to verify the contact configuration, dimensions and ratings. This is an example for understanding selection, not a universal replacement recommendation.
When requesting a quote, include both the manufacturer’s ordering code and any corresponding part number on your approved BOM. If alternatives are acceptable, ask for them to be listed separately for engineering review.
Questions that come up before ordering
Can an SPDT switch replace an SPST switch?
It may provide an on/off function by using the common and one selectable contact, leaving the other unused. That does not make it a drop-in replacement: ratings, action, mounting and terminal layout must still match the application.
Is a three-position switch always DPDT?
No. An SPDT switch can have three positions, such as ON-OFF-ON. Position count and pole count describe different properties.
Are DPST and DPDT interchangeable?
No. DPST opens or closes two circuits; DPDT provides two changeover contact sets. A DPDT device can sometimes be wired for an on/off function, but the complete electrical and mechanical requirements still need to be checked.
Is ON-OFF-ON the same as ON-ON-ON?
No. ON-OFF-ON specifies an open center position. ON-ON-ON uses a connected center configuration that must be read from the exact model’s contact table. Do not infer that configuration from terminal count.
Request the right switch, not just the same shape
For an existing part, send the full manufacturer part number, quantity and required delivery date. For an unidentified switch, include photographs of its markings and terminals, the required operating action, load details and mounting dimensions. Photographs alone are not enough to approve a replacement.
If you are preparing a larger component enquiry, our BOM sourcing guide explains how to organize part numbers and purchasing requirements.
Send EASYIEE your toggle switch part number or BOM for a quote. State whether you need the exact part or would consider engineering-approved alternatives. Availability, lead time and packaging should be confirmed for the specific enquiry.
