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Is multiway switching at two locations with SPST switches possible? Normally SPDT switches are used for this, right?

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No it isn't. A simple multiway system such as both ends of a corridor relies on normally closed and normally open switches operating in tandem at each end. I hope I'm wrong because it's more important to learn than be correct.

If of course you use an SPST to control a changeover relay contact then I'm presuming that would be cheating!

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  • \$\begingroup\$ Normally open or normally closed has (to my mind) nothing to do with SPDT switches, because one throw is closed while the other is open at all times, making the label "normally" ambiguous. Also "in tandem" implies that the switches somehow operate simultaneously, but they are completely independent. \$\endgroup\$ – JYelton Oct 7 '13 at 3:00
  • \$\begingroup\$ @JYelton A normally open and normally closed switch (in tandem) can form an SPDT switch as shown in your drawing i.e. NO and NC with a common connection to each = SPDT. \$\endgroup\$ – Andy aka Oct 7 '13 at 7:18
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Yes! It can be done with four sPsT switches:

diag 1 Switches need to be connected from the opposite poles and each pair needs to be actuated simultaneously.

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  • \$\begingroup\$ This should be the accepted answer. Very creative! \$\endgroup\$ – jdk1.0 Aug 2 at 21:33
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As phrased, your question doesn't specify how the switches are expected to operate.

I'll assume you are referencing a three-way switch arrangement, commonly used in residential wiring to control a light from two distinct locations. In this scheme, the switches are SPDT and are arranged such that the light may be turned on or off from either location:

3-way switch wiring

(From ezdiyelectricity.com)

Either switch can be used to change the light state.

If both switches are SPST, then the following options exist:

  1. both switches closed to enable the light; one open to disable
  2. one switch closed to enable the light; both open to disable

To demonstrate this:

schematic

simulate this circuit – Schematic created using CircuitLab

The use of SPST switches to control a single load is typically used when safety or security is a factor, rather than convenience.

In example 1, this arrangement is used to allow multiple emergency stop buttons to disable a machine. Example 2 would be less for safety and more for convenience, but is rarely used because all switches must be open to disable the device. It would be more useful using momentary switches, for example, where it might be used to allow the starting of equipment from various convenient locations.

You wouldn't want to do this for a light in a hallway because you would sometimes have to travel to both switches to get the desired result.

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No, multiway switching requires two SPDT switches. Multiway wiring methods like staircase wiring, carter wiring, coast 3-way wiring, etc are by using two SPDT switches.

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