Mechanical switches come in two basic types depending on the switching action. Permanent or Momentary.
Switches are also categorised by the arrangement of the switch contacts.
With the Permanent type, the switch changes from On to OFF (or OFF to ON) and remains permanently changed. Another switching action is necessary to change the switch back. Permanent Mechanical switches use either a hinged arm or sliding contacts.
Toggle, Rocker, Slide, Rotary and Key switches are examples.
The simplest switch has a movable arm pivoted at one end moving between two positions, ON or OFF. When the switch is ON, a contact on the arm is touching a fixed contact allowing current to pass. When the switch is OFF the contacts are not touching.
The arm is sprung so that it rapidly snaps open and close. The arm is moved by a Toggle or Rocker.
|Toggle Switch||Rocker Switch|
To control circuits, it is necessary to have different arrangements of switch contacts from the simple On/Off to a Double Pole, Double Throw reversing slide switch with a centre OFF.
|Double Pole Single Pole|
The majority of switches are used to control one wire in the circuit, switching On and Off one current flow. These are called SINGLE POLE switches or SP.
Switches can be made that combine two separate switches in one housing switched with only one operation. These control two separate conductors in the circuit, switching ON and Off two current flows at exactly the same time. Theses are called DOUBLE POLE switches or DP.
The dotted line shows that the two arms operate together. In some circuit diagrams, the two parts of the switch are positioned in different parts and the dotted lines will show that they operate as one.
Perhaps the name comes from the arm being moved or thrown from one contact to another.
Double Throw DT moves between two contacts. Single Throw ST only moves to one contact.
Double Throw Toggle switches also come with a centre OFF position. Look at the manufacturer's specifications for switches in a catalogue.
In this type of switch, a moving contact is made to slide over fixed contacts either in a straight line or in a rotary motion.
Slide switches are supplied in three main contact arrangements.
|3 Pole 4 Way||4 Pole 3 Way|
POLES = Number of Inputs.
WAYS = Also called Throws are the number of switched outputs.
With the momentary type, a force has to be applied to change the switch from ON to OFF (or OFF to ON). When the force is removed, the switch immediately returns to its original position.
Push, Reed and Micro switches are examples.
|Push Switch||Interlocking Push Switch|