Many industrial processes utilize motor control circuits and a number of switches. However, there are two basic types of switches used, momentary contact and maintained contact types. Illuminated push button switchesare typical momentary contact mechanisms and toggle switches are examples or maintained contact switches. Let’s look at what momentary contact is and why it is so important to industry today.
Standard Switch (Maintained Contact)
A standard single pole switch is easy to understand. For example, when you enter a room and flip the light switch up, the light comes on. Power to the light is fed through the switch and the “up” position connects the circuit, while the “down” position disconnects power. This is done by either connecting or breaking a set of contacts which is in series with the light circuit. Most non-illuminated and illuminated push button switches do not work in this manner.
Pushing a Button (Momentary Contact)
A push button switch works with a button connected to a contact. When pushed, it makes connection with another contact but a spring mechanism releases the button once you remove pressure from it, breaking the connection. This can also work in reverse. For example, non-illuminated and illuminated push button switches can be used as emergency stop buttons, breaking contact when pressed.
Why Momentary Contact?
Momentary contact switches are used in situations like motor control and AC/heat circuits. Pushing a button (or turning a switch) energizes a magnetic coil, bringing two sets of contacts together. Once the button is released, the circuit remains closed and the motor or compressor keeps running. When a thermostat is wired in series, it can continually open and close (in response to a temperature sensitive spring mechanism) and this allows for an automatic operation. This is how an AC system turns itself on and off.
