Railwayscenics list various different types of switches and it is easy to be confused by the sheer variety.

TECHNICAL DEFINITIONS:
• Pole - number of switch contact sets.
• Throw - number of conducting positions, single or double.
• Way - number of conducting positions, three or more.
• Momentary (non-latching) - switch returns to its normal position when released.
• Open - off position, contacts not conducting.
• Closed - on position, contacts conducting, there may be several on positions.

SLIDES, TOGGLES, ROTARIES & PUSH SWITCHES

With Slide Switches the switching movement is in a linear to and fro motion. They cost little, the range is limited and they mount discreetly.

Toggle Switches have a to and fro switching movement but through an arc. They cost more than ‘sliders’ but the bigger range will cover almost any switching situation. They are easy to install and look good on a track diagram or switchboard.Toggle switches are the most familiar switches. The simple toggle switch is available in various configurations depending on the number of poles and switching positions.

Rotary Switches, needless to say, have a rotary switching movement. They will be needed when the number of circuits that need to be changed simultaneously exceeds the capacity of a toggle or slide switch.

Push Switches can be either latching or momentary (non-latching). They are usually a simple on-off switch.

POLES AND THROWS

SPST or Single Pole Single Throw – The single throw electrical switch is an "on-off" type switch. One flip of the switch turns the light on, Flip the switch the other way and it turns off. Used mainly to interrupt current for a single pole of a circuit.

DPST or Double Pole Single Throw - -A double throw switch is an "either-or" type switch. You have either one light on or another but not both. Or you have either one section of track powered on or another but not both at the same time. In other words, if you flip the switch one way, Light A comes on and Light B goes off. Flip it the other way, Light B comes on and A goes off.  This switch could isolate both live and neutral poles or one could use it for switching two different circuits simultaneously.

SPDT or Single Pole, Double Throw (ON-ON) - This switch can be on in both positions, switching on a separate device in each case. It is often called a changeover switch. For example, a SPDT switch can be used to switch on a red lamp in one position and a green lamp in the other position.  A SPDT toggle switch may be used as a simple on-off switch.

SPDT Centre Off - ON-OFF-ON - A special version of the standard SPDT switch. It has a third switching position in the centre which is off. Momentary (ON)-OFF-(ON) versions are also available where the switch returns to the central off position when released.

DPDT or Double Pole Double Throw - Dual ON-ON - A pair of on-on switches which operate together.

DPDT or Double Pole Double Throw Centre-Off - These can be very useful for motor control because you have forward, off and reverse positions. Momentary (ON)-OFF-(ON) versions are also available where the switch returns to the central off position when released.

Rotary (Multi-way) Switches have many conducting positions. They may have several poles (contact sets). They are available with a range of contact arrangements from 1-pole 12-way to 4-pole 3-way.For different variants of the rotary switch, the number of ‘ways’ (switch positions) are reduced with a different ‘stop’ under the fixing nut, limiting the movement where there are more poles to be served.

REED SWITCHES

Magnetic Reed Switches are long thin wire-like switches that are activated by the presence of a magnet. You can place one of these under the track rails between the ties and place a small magnet on the bottom of a railcar, so that when the railcar with the magnet travels over the switch, the device that the switch is connected to will be activated (e.g, a light in a building, a section of track or an animated device).

Normally open
In a reed switch, the two contacts (which look like metal reeds) are made from magnetic material and housed inside a thin glass envelope. (You can see this quite clearly in our top photo.) As you bring a magnet up to a reed switch, it magnetizes the contacts in opposite ways so they attract and spring together and a current flows through them. A reed switch like this is normally open (NO) (normally off), unless a magnet is positioned right next to it, when it switches on.

Normally closed

You can also get reed switches that work the opposite way. The two contacts are normally snapped together. When you bring a magnet up to the switch, the contacts magnetize, repel one another, and split apart, opening the switch and breaking the circuit. Reed switches like this are called normally closed (NC) (normally switched on), and they switch off when you bring a magnet up to them.