Normally open (NO) and normally closed (NC) are different terms used widely in the electrical world when referring to switches. Plash is familiar with this part of electrical components, so we will explain what each of these means, how they work, and give some examples of where they can be used.
Now let's dive deeper into normally open vs. normally closed switches.
What Does Normally Open Switch Mean?
Normally open means that the switch or contact (when it is not compressed or activated) doesn't let current flow through in its normal state. The diagram below shows that when the switch is in its unpowered/original state, it allows the current to flow through it. When the switch becomes activated or compressed, it opens the circuit and causes the flow of currents to stop.
Normally open contacts and switches can either be momentary or latching switches:
- Momentary Switches - These only change state for the duration it is pressed or activated.
- Latching Switches - These change state when it is pressed once, then pressed again to change it back to the original position.
Where Are Normally Open Switches Used?
When a switch is normally open, the power and electrical current flow through. Normally open switches are used in many different ways. Below are a few examples of normally open switches.
When a light switch is in the ‘On’ position, the power flows, and the switch is open. Then when it is turned off, the power and current stop and no longer flow through the switch.
Normally open switches can be push buttons that, in their default state, make no electrical contact with a circuit. This means that when a start button is pressed, whatever device or machine it controls will power up.
A reset button is another example of a normally open push button. Similar to a power button, it will only close or reset when the button itself is pressed.
Other applications are:
- Normally open contact blocks.
- Normally closed relays.
What Does Normally Closed (NC) Mean?
A normally closed switch or a contact switch is a switch that allows electrical current to flow through when it is in its normal state (not compressed or activated). In the diagram below, you will be able to see what the switch looks like in its normal state and when it is activated. Current is always flowing through the switch until it is activated or compressed, then the flow stops.
Where Are Normally Closed Switches Used?
Normally closed switches are used in many different applications. Emergency stop buttons are some of the most common. Once the button is activated or compressed, the power is cut off, and the machine or equipment will shut down.
Emergency Stop Buttons
Emergency stop buttons used normally closed switches for safety reasons. It is a safety device that will power down machines instantly in the case of an emergency.
The normal default for stop buttons is using a normally closed switch. Based on the normal state and active state of this type of switch, pressing the ‘stop’ button will then activate the switch causing the electrical current to stop flowing through.
Other applications are:
- Normally Closed Contact Blocks.
- Normally Closed Relays.