Application manual for YRB-4EML-31S safety relay
Contrinex AG Industrial Electronics
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4.6 Contact extension/forcibly guided contacts
Often more contacts are required than are available as standard. For these applications, the
forcibly guided contact extension modules are used. They can be connected as modules as
required.
Forced guidance
Standard EN 50205 makes a distinction between two groups of relays with forcibly guided
contacts:
– Application type A: relay with forcibly guided set of contacts
– Application type B: relay with a forcibly guided set of contacts and other contacts which
are not forcibly guided, as well as a contact set with PDTs
The definition of
“forced guidance” according to EN 50205 is:
The relay must be designed so that none of the mechanically connected N/C contacts can
close if a N/O contact is closed and none of the mechanically connected N/O contacts can
close if a N/C contact is closed.
These requirements apply for the entire service life of the relay and for reasonably
foreseeable failure conditions.
The effects of reasonably foreseeable breaks and/or wear on parts of the elementary relay
must not cause the (mechanical) forced guidance to fail.
During the entire relay service life specified by the manufacturer, the contact distances of
opened contacts must be greater than 0.5 mm for a single N/C contact and greater than
0.3 mm each for a double interrupt. (Mechanical) forced guidance of contacts means that
none of the N/C contacts can close if a N/O contact does not open for the non-activated
relay. In addition, none of the N/O contacts can close if a N/C contact does not open when
the relay is activated.
