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POWER CIRUCITS
12 ME00070B TMS7 SERIES
5.7 Line contactors
The TMS7 is designed to operate with or without a line
contactor. In many regions there is a statutory requirement that
a line contactor be employed with electronic motor control
equipment. From a safety point of view, this is the preferable
option, however is not necessary for starter operation. An
additional benefit gained by use of a line contactor is isolation of
the starter SCR’s in the off state, when they are most
susceptible to damage from voltage transients.
The TMS7 can directly control a line contactor via the Main
Contactor Control output.
As an alternative to a line contactor, either a circuit breaker with
a no volt release coil operated by the TMS7 trip output, or a
motor operated circuit breaker can be considered. If a motor
operated circuit breaker is used as a line contactor, the potential
delay between the breaker being told to close and phase power
being applied to the TMS7 could cause the TMS7 to trip on
installation faults. Closing the motorized breaker directly and
using the breaker’s auxiliary contacts, or preferably a slave relay
with gold flash contacts, to control the TMS7 can avoid this.
Line contactors must be selected such that their AC3 rating is
equal to or greater than the full load current rating of the
connected motor.