What do you call a pair of SPDT switches controlled by one toggle?

Question

I need a toggle switch which allows me to switch the poles of two separate single-pole-double-throw switches together. It would work like the diagram below. Note that the dotted line represents a physical connection not an electrical one.

diagram of double SPDT

I need to find one online (for UK shipping). What are they called?

score 18 · Accepted Answer · answered Feb 26 '15 at 15:18

18

We call it a "DPDT" (Double Pole, Double Throw).

answered Feb 26 '15 at 15:18

Ignacio Vazquez-Abrams

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Now that was a hard one to figure out after knowing its *two* SPDT ;) – PlasmaHH Feb 26 '15 at 15:21
3PDT and 4PDT toggle switches are also readily available. The same terminology also applies to relays. – Peter Bennett Feb 26 '15 at 16:34
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Actually Digi-Key lists 6PDT pushbuttons in stock, and 8PDT and 10PDT (but not in stock). – tcrosley Feb 26 '15 at 18:16
There was a recent question with [these](http://www.lightcountry.com/download/slide/Slide%20Switch%20SS%20Series-11.pdf), and then there's [these](http://www.taydaelectronics.com/electromechanical/switches-key-pad/rotary-switch.html). – Ignacio Vazquez-Abrams Feb 26 '15 at 18:22
It's all good until the DPDT is on on on, and then smoke starts coming out of my ears. – Scott Seidman Feb 26 '15 at 22:49

score 13 · Answer 2 · answered Feb 26 '15 at 17:04

The term xPyT [or "x pole y throw"] generally refers to a switch assembly which has x ganged-together switches, all of which have y active positions, but when x or y would be 1 or 2, the letters "S" and "D" are used instead. Thus, DPDT is two switches each with two active positions.

Generally y will indicate the number of positions to which a switch may be set, even if some or all of the ganged-together switches don't have contacts for all positions, but there are a few notable exceptions:

A switch assembly which has two positions, and one of those positions doesn't connect anything, will be referred to as "ST" [single throw] if the switch will stay put in either the connected or unconnected position, "NO" [normally open] if it is spring-loaded to the open state, or "NC" if it is spring-loaded to the closed state.
It's common for switch assemblies to have two positions that close contacts, and a stable center position which doesn't close anything. Such a switch assembly with e.g. two switches would be referred to as "DPDT center off".

While most switch assemblies fit the xPyT nomenclature or one of the two patterns above, some do not. Some contacts may be missing, and some combinations of contacts may be permanently wired together. A few combinations have special names. For example, the term "reversal switch" [or, in residential lighting, "four-way switch"] is often used to describe a DPDT switch assembly where the upper contact for one switch is connected to the lower contact for the other and vice versa. Some other combinations may be easily described as being a like a xPyT switch assembly but with some changes (e.g. a "3P3T switch with no connections for a far-left "off" position, or a "12PST" switch assembly where all of the switches have one contact in common. If an assembly deviates too much from any "normal" pattern, however, a schematic may be the clearest way of describing it.

+1 because I remember how painful this notation was before I actually understood it — Greg d'Eon, Feb 26 '15 at 17:44
a really fun common oddball switch is the three position bidirectional three phase switch. It has three poles and six connections. when set to off everything is open, when set forward the three inputs are connected to the three outputs, when set to reverse, Two of the outputs are swapped and the third connects as normal. — hildred, Feb 26 '15 at 20:11

What do you call a pair of SPDT switches controlled by one toggle?

2 Answers2