Application examples using the modular safety relay system
102597_en_03 PHOENIX CONTACT 117 / 136
7.2 Contact extension/force-guided contacts
Often more contacts are required than are available as standard. For these applications, the
force-guided contact extension modules are used. They can be activated module-by-mod-
ule, if required.
Forced guidance Standard EN 50205 makes a distinction between two groups of relays with force-guided
contacts:
– Application type A: relay with a set of force-guided contacts
– Application type B: relay with a set of force-guided contacts and other contacts which
are not force-guided, as well as a set of contacts with changeover contacts
The definition of “forced guidance” in accordance with EN 50205 is:
The relay must be designed so that none of the mechanically connected N/C contacts can
close if an N/O contact is closed and that none of the mechanically connected N/O contacts
can close if an N/C contact is closed.
These requirements apply for the entire service life of the relay and for reasonably foresee-
able 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 may close if an N/O contact does not open for the non-activated
relay. In addition, none of the N/O contacts may close if an N/C contact does not open when
the relay is activated.
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