What does positive opening mean?
Positive opening is a safety principle that describes the mechanically forced opening of contacts. In contrast to conventional switching contacts, where closing or opening processes can fail due to wear or sticking, positive opening ensures that a contact opens reliably in the event of a fault.
The technical basis is the standard DIN EN 60947-5-1, which precisely describes the behaviour of positively driven contacts in Appendix K. It states the following:
The separation of the contact must be triggered directly by the defined movement of the actuating element - and must not depend on components such as springs. This is the only way to ensure that the contact opens reliably every time it is actuated.
Why is positive opening so important?
In practice, high inrush currents, inductive loads or long switching cycles can lead to welding or contact erosion.
However, in safety-critical applications - such as in machine control systems, emergency stop circuits or door monitoring systems - it is crucial that circuits are reliably interrupted in the event of a fault.
If a contact remains closed, a safety risk arises and this can have serious consequences:
- Danger to human life
- Damage to machines and systems
- Increased fire risk
This is why positive opening is an indispensable element in the safety design of modern machines and systems.
How do you recognise switches with positive opening?
In safety-related applications, it is crucial that only switches with documented positive opening are used. But how can these switches be reliably identified?
- Symbol labelling on the switch housing
Every auxiliary current switch with positive opening must be permanently and easily legibly labelled on the outside with the following symbol:
IEC 60617-S00226 (2001-07) - Information in technical data and catalogues
The data sheets, catalogue pages or type code declarations from BERNSTEIN also state which contacts are positively driven. There you will find formulations such as
"Contacts, positive opening" or "Suitable for safety applications in accordance with DIN EN 60947-5-1 (positive opening)"
Practical tip:
If you want to be on the safe side, pay attention to the symbols on the housing during the selection process, check the information in the data sheet and clarify with the manufacturer whether positive opening is present if you are unsure - a must, especially for safety-related control circuits.
Understanding positive openingProducts, knowledge and practical solutions from BERNSTEIN
If you are interested in the subject of positive opening in industrial safety technology or are looking for suitable products for your application, you will find a selection of additional materials and product ranges from BERNSTEIN here.
Tip: For specific applications or support in selecting suitable switch types, our sales team will be happy to advise you.
