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wiring a dpdt switch like a dpst switch Answered

i need a DPST rotary switch so that i can turn on two circuits at once but the closest i've been able to find with appropriate ratings is a DPDT switch, is it possible to wire it up to my circuits in such a way that it works like a DPST switch?

I've attached an example diagram i found of a DPDT switch, if i was to disconnect the lamp from pin 1 and the buzzer from pin 2 would the first position of the switch become Off and the second position become On powering the LED and speaker? also assuming that the LED and speaker only connected back to their respective batteries and not to each other, could i attach a low voltage battery to pin 3 for the LED and a higher voltage battery to pin 4 for the speaker without causing damage?



5 months ago

The switch at the current position as shown above will connect 3 - 1 (lamp will light up) and 4 - 2 (the buzzer will operate) - in order to convert a dpdt to a dpst do not connect to 5 and 6. On AC circuits 3 can be connected to the live wire and 4 to the neutral - this shuts off but live and neutral when in the "off" position in order to prevent a "shock" when a motor or a capacitor may have residual current in it.

Check for rotary cam selector switches in the industrial supply area.
Something like this for example:


If you go to a real shop they can show you different models.
Some come with "drums" in 1, 2, 4 or even 8 poles, others come in 1 or pole by means of push in switch blocks that are replaceable, meaning you can use NO or NC blocks.

unfortunately there isn't really anywhere locally to me that sells useful components like this so i sent an email to RS components online shop asking for DPST switch suggestions and they suggested this DPDT switch: http://uk.rs-online.com/web/p/products/0351140/ and told me that it would be fine but didn't include any info on how that would work. i tried googling to see if there were examples of DPDT switches wired up as DPST switches but so far i haven't found anything. so could i omit 2 of the contacts and use it as a DPST or would that not work for some reason?

A DPST is two independent SPST in one switch. (SPST is just on/off)

A DPDT is two SPDT switches in one. (SPDT switch one line to two different ways. If one of those ways connects to nothing, it is simply off).

You should be able to achieve your desired outcome with a DPDT. I've provided the links to the datasheets for the switch RS recommended (in case you missed them on the RS page).



thanks, i did try looking at the data sheet but i lack the knowledge to fully comprehend them, your explanation is much easier to follow so i'll purchase a switch and hopefully it'll all work out :)

If in doubt you should find switch symbols on your new switch.
Next to each dot, representing a contact point there should be a number.
Near each contact on the switch you will find these numbers.
What you see on the switch symbol is the normal state of the switch, so if a contact is shown closed it means in the neutral position this contact will have a short.
The open contact will have the short when you move the switch in the corresponding direction while the other contact of this block will open at the same time.

Should work the same way if you get the right type with two integrated switches.