Key switch is a type of switch that can only be turned on and turned off by using a key. Only a key partner and the right locking device which can be used to operate the switch. Key switch can be used in applications that require high levels of security, such as electrical control circuit in the industry.
Examples of key switch as shown in the picture below
Toggle switch, rocker switch, and slide switch, can also be made in a Double Pole Double Throw version, which is abbreviated with DPDT switch. Form of this switch combine two separate switches in one unit, but they operated together.
DPDT switch can be used to connect two circuits at the same time. These switches can also be connected to the neutral wire line and the line wire voltage of the source at once. When a switch is in off state, the electrical equipment connected to the switch is totally isolated from the source voltage.
Symbol of DPDT switch as shown in the picture below