Question:

What is the difference between an emergency stop switch and a standard push button switch?

Answer:

Standard push button switches, such as the A22N series pictured below, are typically used for machine controls, such as starting operation or changing modes.

They also have a range of options as to their appearance and operation. For example, the A22N can be fitted with illumination, different colours, and Normally Open or Normally Closed operation.

In contrast, an emergency stop switch, such as the A22NE series pictured below, are used as a safety device to stop hazardous elements of machines.

As such, an emergency stop switch must be highly visible in colour and appearance, as well as easy to locate and operate in emergency situations. 

Emergency stop switches operate using Normally Closed circuitry, though they may have a Normally Open element for auxiliary controls. Once operated, the button must remain engaged until disengaged by a deliberate action (such as twisting the button clockwise). The button must also be red, with a yellow background.

It is important that standard push button switches are not used where emergency stop switches are required. This can lead to the failure of a safety system, and expose workers to hazards.

Note that the appearance and operation of an emergency stop switch is only one element in a broader safety system. For advice on a complete safety system, please contact Omron directly.