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enter image description hereI would just like to ask a question about a SPDT switch. In general, just considering the regular generic SPDT switch only, the 'tip' (example only) of the switch has only two possible 'contact' points (options) that it can pivot to ----- with no stable (third) 'off' position.

There appears to be another sort of SPDT switch that has a stable (third) 'OFF' position, where the tip can remain - where the tip is not contacting the two optional contact points. That is, a three-way switch that has a central stable 'off' position, but would otherwise be a SPDT. Is there a regular name for this variation (with the stable third 'off' position)? That's only if it really is a variation of a SPDT switch. Thanks!

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It's also known as a '3-way, centre-off' switch.

The following edit is necessary to correct the above erroneous answer and furnish more details for clarity:

The above answer is incorrect with respect to usage of the term 'way'.

The correct answer would be 'It's an SPDT, centre-off toggle switch'.

The following are standard configurations of toggle and rocker switches:

SPST: single-pole, single-throw

SPDT: single-pole, double-throw

DPST: double-pole, single-throw

DPDT: double-pole, double throw

SPDT, centre-off: single-pole, double-throw with centre-off

DPDT, centre-off: double-pole, double throw with centre-off

Here are some commonly used terms:

Pole: number of switch contact sets or number of circuits that are controlled by the switch

Throw: lever movement that establishes a terminal contact (used for standard toggle and rocker switches)

Way: lever movement that establishes a terminal contact (used for rotary and slide switches)

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    \$\begingroup\$ 'Single-pole, 3-way, centre-off switch' would be more appropriate. \$\endgroup\$
    – vu2nan
    Oct 7, 2021 at 7:03
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    \$\begingroup\$ Hi Kenny, The word 'throw' is relevant to toggle & rocker switches. It refers to the lever movement that establishes a terminal contact (e.g. 'single-throw', 'double-throw'). The word 'way' is used with rotary and slide switches in which more contact positions are possible. The word 'pole' is used to refer to the number of circuits that are controlled by the switch. \$\endgroup\$
    – vu2nan
    Oct 7, 2021 at 9:58
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    \$\begingroup\$ n-way when refering to toggle/rocket switches seems to be a term mostly used by electricans, not by people designing electrical equipment. Worse it's used differently by british electricians and american electrians. \$\endgroup\$ Oct 7, 2021 at 16:50
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    \$\begingroup\$ Hi Peter & Kenny, I have to thank Peter for his comment which opened my eyes to an error in my answer with respect to usage of the term 'way'. It is essential that I correct it and furnish more details for clarity. My sincere apologies for the inconvenience. \$\endgroup\$
    – vu2nan
    Oct 7, 2021 at 17:58
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    \$\begingroup\$ I mean it's not "wrong" wrong to use "way" that way. Many people would say 3 way switch and would understand what was meant. \$\endgroup\$
    – Passerby
    Oct 8, 2021 at 2:19
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I would call an SPDT switch with a center off position an "SPDT, center off" toggle switch.

You can also get toggle switches that are momentary in one position.

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  • \$\begingroup\$ Thanks so much Peter! That sounds good. Definitely happy with that description. I will go with that description. Nice! Much appreciated. \$\endgroup\$
    – Kenny
    Oct 7, 2021 at 5:22
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    \$\begingroup\$ You can get them momentary in both positions too. (Momentary On / Off / Momentary On) \$\endgroup\$
    – Passerby
    Oct 7, 2021 at 5:27
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These are known as On-Off-On switches. Though it is not specific to SPDT switches. The same applies to center off DPDT and nPDT switches.

Also spelt On/Off/On or (ON)OFF(ON) or any number of variations in punctuation.

Oh, and there are Off / On / On, Momentary On / Off / On, Momentary On / Off / Momentary On switches as well. These are less common but still available as off the shelf parts.

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    \$\begingroup\$ Thanks as well Passerby. So we can call them On-Off-On SPDT ? Much appreciated also. \$\endgroup\$
    – Kenny
    Oct 7, 2021 at 5:25
  • \$\begingroup\$ Yes. Even big distributors like Mouser use that the On off On phrasing for these. \$\endgroup\$
    – Passerby
    Oct 7, 2021 at 5:26
  • \$\begingroup\$ That was super helpful. Thanks again Passerby. Greatly appreciated. \$\endgroup\$
    – Kenny
    Oct 7, 2021 at 6:00
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    \$\begingroup\$ Parentheses are often used to denote a momentary position. So on-off-(on) would have a permanent on position, center is permanent off and the other position is a momentary on. \$\endgroup\$
    – rve
    Oct 7, 2021 at 14:56
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    \$\begingroup\$ For example uk.rs-online.com/web/c/switches/rocker-switches-accessories/… if you go to "switch configuration" you will see various permutations of what is being discussed here \$\endgroup\$
    – Rodney
    Oct 8, 2021 at 10:59
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Not exactly what you are searching for, but the variant where the third position also has a contact is widely called "SP3T". "SP4T" is used as well, anything above that is just "N-way switch".

You can buy an SP3T and just have one contact not connected.

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  • \$\begingroup\$ Thanks Vladimir. Definitely --- the SP3T is certainly closely related to the right-hand switch in my diagram. The SP3T could definitely serve to perform the same functions as the switch on the right-hand-side of my diagram ----- for the case where the central contact is just left alone - such as not connected to anything significant. \$\endgroup\$
    – Kenny
    Oct 8, 2021 at 9:53
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At least in the case of semiconductor analog multiplexers, most suppliers and manufacturers seem to have SPDT parts available that have an additional 'enable', or 'output enable' pin. However, many part selectors don't allow you to filter on this feature. Furthermore most multichannel SPDT parts only have a single 'enable' switch for all of the channels grouped together.

An example of this would for instance be the TI TMUX1575: the enable pin is only mentioned in the diagram, and in the datasheet only on the third page and beyond.

TMUX1575

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  • \$\begingroup\$ With 'output enable' ----- that would probably be equivalent to having an SPST switch in series with one of channels. Eg. for channel #1 ---- having an SPST switch somewhere between the existing SPDT and the pin D1. \$\endgroup\$
    – Kenny
    Oct 8, 2021 at 22:31

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