QUESTION:
Does it make sense to use "weld-free" contactors in safety relevant
controllers?
ANSWER:
Apart from the assignment types 1 and 2, there are no test
conditions for weld-free short-circuit protection of contactors in
the regulations for contactors and motorstarters (IEC 60947-4-1).
(Expensive) self-directed tests taking into account only the two
standardized test currents Ir and Iq would not reflect real life
conditions.
The manufacturer specification "weld-free" for contactors is only
valid in case of short-circuits. Every contactor welds at the end
of the contacts' service lives or with faulty control commands
(chatter commands). For this reason, in our opinion safety when
switching dangerous movements is only possible with redundancy and
self-monitoring but not by using weld-free contactors.
Entry ID:21384983
Date:2005-04-04
This entry is available in the following languages: chinese
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