Kill Switch

A kill switch is a nickname for an emergency stop button. The nickname is perfect, as an emergency stop literally is meant to kill the machine it is connected to. Emergency stop buttons should not be mistaken with a regular shutdown button. Shutdown buttons are meant to stop a machine or process in steps, so as to not damage anything, while an emergency stop is meant to stop the process as soon as possible even if it means damaging the machine. Companies do this to prevent injury or further injury even at the cost of losing a machine.

These switches can take many different forms but most kill switches we are used to seeing today are usually the big red buttons with EMERGENCY STOP, that is visually noticeable for everyone. They are meant to push in, so anybody can operate it even if impaired.

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Digi-key uses a rope system connected to an emergency stop button all around the belt system, so no matter where you are, you should have access to the red rope to pull in an emergency.

Kill switches are not only in industrial settings but can be used with your own products. Many people place kill switches in vehicles to prevent them from being stolen, basically using a toggle switch like the S301T from NKK Switches.

EAO, one of Digi-keys suppliers for emergency stop switches, has provided a Digital Product Selector Tool for Emergency Stop Switches. EAO makes it easy by choosing from a variety of options to fit your application.

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Digi-key provides Emergency Stop buttons in many different styles to fit your needs.

Digi-key also provides accessories such as the emergency stop plate.

If you would like to design something simple you can find our switch category here.

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More specific requirements about emergency stop switches are specified in the European standard EN 418 (International Standard: ISO13850) as follows:

All Emergency OFF devices must be “self-latching” (maintained) devices. With regard to emergency stop switches, this means it must be either a “push-pull” or “twist-to-release” device.
The latching mechanism must be engaged prior to the electrical contact change-of-state to avoid a momentary OFF signal.
All devices must have a “mushroom” head that is red in color.
The background immediately surrounding the Emergency OFF device must be yellow in color.
All Emergency OFF devices must have positive opening (direct opening) operation. This means there must be a direct mechanical link between the operation of the mushroom head and the contacts to drive the electrical contacts open. This protects against a potentially unsafe condition should contacts weld. A spring action contact does not comply with this requirement.
The devices must not be reset automatically; manual reset is a requirement.

Regarding the function of the normally open contact, there is no difference between a general-purpose button switch and an emergency button switch.

The general button switch has no direct disconnection mechanism on the normally closed contact. If the contacts are soldered, they will remain conductive and the device cannot be stopped under dangerous conditions (load). If this happens, the device may continue to be in a dangerous state. Therefore, for safety applications, please use the normally closed contact of the emergency stop button switch.