Glossary · Stopping functions and safe states
Emergency switching off
Also known as: emergency power-off, EPO
German: Not-Aus
In machine safety, emergency switching off is an emergency action intended to remove electrical energy from all or part of an installation where electrical hazards, such as a risk of electric shock, are involved.
- Machine safety
- Technical documentation
In one sentence
Emergency switching off cuts electrical energy in an emergency where electrical hazards exist. It is not the same as an emergency stop.
Example
In an electroplating plant with exposed live conductors, an emergency switching-off device at the entrance disconnects the incoming supply to the bath rectifiers when someone is at risk of electric shock.
How it applies
- Machine safety: Emergency switching off is provided where the risk assessment identifies electrical hazards that call for it. Removing the supply usually results in an uncontrolled stop comparable to stop category 0, so check whether that stop creates new hazards, for example falling loads.
- Technical documentation: Name the function precisely. Operating manuals often label every red button “emergency off”; state which device stops motion and which disconnects power, and what stays live.
- Maintenance: Emergency switching off is an emergency action. It does not isolate the machine for work; that needs energy isolation with lockout/tagout.
- Evidence: Wiring diagrams and test records should show which circuits the device disconnects.
Emergency switching off vs. emergency stop
The emergency stop stops hazardous operation, and power may remain available to achieve a controlled stop. Emergency switching off removes electrical energy because electricity itself is the hazard. Using one term for both leads to wrong device selection and misleading instructions.