Is multiway switching at two locations with SPST switches possible? Normally SPDT switches are used for this, right?
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!
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:
Either switch can be used to change the light state.
If both switches are SPST, then the following options exist:
- both switches closed to enable the light; one open to disable
- one switch closed to enable the light; both open to disable
To demonstrate this:
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.