Last edit: 09/01/2026
Why are well-tried components important in Machinery Safety?
The concept is defined in both ISO 13849-1 and IEC 62061. Here is the definition:
[ISO 13849-1] 3.1.50 well-tried component
Component successfully used in safety-related applications
A well-tried component for safety-related applications is a component which shall be
- Either widely used in the past with documented successful results in similar applications. This aspects opens the door to the “proven in use” concept of IEC 61508-2, or
- Listed in the informative annexes A to D of ISO 13849-2:2012, or
- Made, verified and validated using principles which demonstrate its suitability and reliability for safety-related applications according to relevant product and application standards.
It remains as a key guideline that a particular component can be considered as well-tried only if suitable for the specific application, considering for example the environmental influences.
A switch with positive mode actuation is a well-tried component if it complies with IEC 60947-5-1, Annex K. That means if a manufacturer has a new switch in his product range and it complies with the above standard, it is a well-tried component from the first unit produced. However, if a manufacturer has a new component not mentioned in the annexes of ISO 13849-2 and he wants it to be defined as well-tried, he needs to use it extensively first.
Those types of components are compulsory for Category 1 (ISO 13849-1) and in Architecture A (IEC 62061), architecture without redundances and Diagnostic Coverage. In all other Categories and Architectures not well-tried components can be used, provided they have Reliability data.
Despite opening the door to the Proven in Use concept, both standards make it clear that complex electronic components (e.g. PLC, microprocessor, application-specific integrated circuit) cannot be considered as equivalent to “well-tried”.As a generak rule, the concept of well-tried components is not the same as Proven in Use according to IEC 61508 or Prior Use according IEC 61511-1.
There are PLC manufacturers that have input, and output Digital modules with reliability data, but only if used in a redundant (1oo2) configuration. The reason is that in a single configuration it would be a Category 1 according to ISO 13849-1 safety subsystem or Basic subsystem Architecture A according to IEC 62061. In which case, only well-tried components can be used.
Examples of well-tried components are:
- Power contactors built in conformity to IEC 609474-1
- Auxiliary contactors built in conformity to EN 50205 or IEC 609475-1 and IEC 60947-4-1:2001, Annex F
- Relay but only built in conformity to IEC 618103
- Pressure switch built in conformity to IEC 609475-1 for the electrical part and to the Annex B/C for the pneumatic/hydraulic part.
Conclusions
Use of Well-tried components is compulsory in single channel safety systems without diagnostics. They are “simple” components having predictable failure modes. Complex electronics, as well as Inductances, Resistors, Capacitors, Discrete semiconductors and Optocouplers, cannot be considered well-tried components.