What is a Normally Open Switch?

A normally open switch is a type of electrical switch. When a normally open switch is not compressed it remains "off". This is because of the electrical connections inside.

In a normally open switch, when the switch is off the contacts are open. This means the electrical connection is broken so the switch is “off”. In Normally Closed switches, the contacts are closed which connects the switch meaning that when they are not compressed they are switched “on”.

The difference between an open switch and a closed switch is shown in the drawing below

Latching and Momentary Normally Open Switches

Normally open switches can be either momentary or latching. A momentary switch requires continuous compression whereas a latching switch will require the user to press once to change state.

Examples of a Normally Open Switch

The majority of switches are normally open. A few examples are;

Light Switch – light switches can be described as normally open latching switches. They are open until they are compressed; they then remain closed until they are pressed again and switched off.

Medical bed controls– medical bed controls can either be footswitches or hand controls and are usually normally open momentary switches. When they are not being compressed the switch remains open, the user must continuously press the switch for the bed to move to the desired height, then, once the user removes the compression the switch is open again and the bed stops moving.

Medical and industrial equipment – many different types of devices within medical and industrial environments will use normally open switches – specifically footswitches. When the footswitch is compressed it will close the circuit to switch the machinery on, examples of this type of application include;

·         Sewing machines

·         Medical machinery

·         Metal cutting machines

·         Metal bending machines

·         Tattoo machines

·         Optical instruments

·         Hair removal devices

Normally Closed Switch

There are some applications where a normally closed switch would be the best option. The main use for a normally closed switch would be an emergency stop. The switch would keep the circuit closed when it has not been pressed. Once it is pressed it will open, causing the circuit to break and the power to be cut.

At Herga we provide change over contacts which allows the switch to be wired normally open or normally closed. This means the switch can be used for a wider variety of applications.

Normally open switches from Herga

Many of our switches are available as normally open or normally closed. The products in our range include;

·         Footswitches

·         Hand controls

·         Microswitches

·         Puck switches

Compare our various footswitches on our foot switch line card.

For more information on normally open switches, normally closed switches or any of the products within our range please contact us.