Monitors contactors
September 1st 2008 A new product from Moeller
Electric is designed to eliminate
the expense of using duplicate
redundant contactors in motor
starters with safety functions. The
company says the same levels of
safety can be achieved using a
compact and inexpensive
Contactor Monitoring Device (CMD).
The CMD modules operate by
monitoring the state of the
contactors main contacts, and
comparing this with the voltage
applied to the coil. If the coil is deenergised
but the main contacts
are not open, the CMD opens a
normally-closed output contact that
can, for example,be used to trip
the starter's motor protection circuit
breaker via an undervoltage release.
This mode of operation ensures
that even if the main contacts of
the contactor weld, the motor it is
controlling is safely brought to a
stop.The CMD monitoring relay
can be used to implement
Category 3 and Category 4 safety
circuits in line with EN 954-1, as
well as safety circuits with
Performance Level d. More articles from Moeller Electric Ltd: | 
