Electronic – I’m having trouble understanding SPST terminology

switchesterminology

Before someone LMGTFYs me, let me get this straight: I HAVE DUCKDUCKGO'ed this already, but I still cannot understand what switch 'pole' and 'throw' mean. I really just need a clearer explanation of switch terminology please!

Best Answer

Think of "Poles" as a piece of wire you want to connect somewhere. And "Throws" as places where you can connect that wire to.

N Poles = N wires

M Throws = M places where you can connect each of the N wires to.

SPST

(Note that on a SPST there isn't necessarily a side which is the Pole or the Throw.)

The following might help you understand the terminology better:

  • To add a "Throw" you just add an extra connection on the right side. (therefore one pin at least, becoming SPDT)
  • To add a "Pole" you duplicate the entire thing, therefore at least 2 pins, becoming DPST.

enter image description here

SPDT

Following is a SPDT. Which means you have a piece of wire you can connect to two places.

  • To add a "Throw", you just need to add a new place to connect it to (one more pin on the right side, having a SP3T).
  • To add a "Pole", you would have to add a piece of wire and two places to connect it to, therefore at least 3 pins and duplicating the entire thing. (Assuming you are maintaining it as Double Throw)

enter image description here

Images are from Sparkfuns explanation.