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Entry type: FAQ Entry ID: 69778886, Entry date: 02/15/2017
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3SE7 cable-operated switches: Achievable safety integrity level SIL (IEC 62061) or performance level PL (ISO 13849-1)

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This entry contains information about the use of 3SE7 cable-operated switches in safety circuits.

QUESTION:

Which safety integrity level SIL (IEC 62061) or performance level PL (ISO 13849-1) can be achieved with 3SE7 cable-operated switches?



ANSWER:

Cable-operated switches with latching and button reset can be regarded as EMERGENCY STOP command devices.

They have a B10d value of 200 000 switching cycles at 10% of the rated load and a maximum service life T1 of 20 years.

The electrical interconnection can be implemented with one channel or two, whereby both contacts are integrated in a switch enclosure.

With single-channel interconnection, a maximum of PL c or SIL 1 is attainable.
With two-channel interconnection, a maximum of PL e or SIL 3 can be attained since the fault detection (diagnostic coverage DC) resulting from the two-channel structure is then 99 %.
This applies both to the processing of 2NC and 1NC/1NO.

Since cable-operated switches are mechanically usually only single channel, from PLd or SIL2 and higher it is necessary to have fault exclusions for the mechanical part of the tripping chain to prevent the cable from getting contaminated and stuck, damage to the switch from external forces etc. This must be carried out individually for every application. When using fault exclusions for a PL e or SIL 3 application, it is advisable to contact the accepting authorities since the use of fault exceptions can result in restrictions in the attainable safety level.

The use of 2 cable-operated switches on one cable is both possible and permissible
and can result in a further improvement in the ratings since fault exclusions on the mechanics are not longer necessary. However this can also make setting the cable tension more difficult or even impossible in some applications.

You can also adjust this constellation with the TÜV-approved Safety Evaluation Tool (SET).


In the Safety Evaluation Tool under the menu item "Library > IEC 62061 or ISO 13849-1" you can find the sub-item "EMERGENCY-STOP".

If you work through the entire application, you will receive at the end a TÜV-certified protocol listing the parameters attained.
This is the equivalent of the written confirmation which some customers require and ask for.
The SET is available to all users after free-of-charge registration.
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