MCD 200 Design Guide
MG.17.C3.02 – VLT is a registered Danfoss trademark 11
MCD 200 Series Overview
Trip output:
The relay operates when the MCD 202 trips on
any fault. This can be used to operate a shunt-
trip mechanism of an upstream circuit breaker to
isolate the motor branch circuit. It could also be
used to signal MCD 202 “Trip” status to an
automation system.
Run output:
The relay operates on completion of start ramp.
This can be used to operate a contactor for
power factor correction capacitors. It could also
be used to signal MCD 202 “Run” status to an
automation system.
• Is the MCD 202 suitable for flying start
application?
Yes. There is a built-in 2 second delay between
the end of one stop and the beginning of the
next start. This delay allows the motor flux to
decay, eliminating any chance of the MCD 202
tripping on Power Circuit fault (x 1 Ready LED
flash) due to detection of motor back EMF when
the start signal is applied. The major effect of a
flying start is on the actual time the MCD 202
“current limits”. The ramp-up time will be
reduced and is determined by the motor speed
on re-application of the start signal.
• What is the remote start and stop input
impedance? Are any special precautions
necessary during installation?
The N1/N2 input impedance is approximately
400 kΩ @ 300 VAC and 5.6 kΩ @ 24 VAC/VDC.
All control wiring, for long runs, should be either
twisted pair or shielded cable with the screen
earthed at one end. Control wiring should be
separated from power cables by a minimum
distance of 300 mm.
If long cable runs cannot be avoided, the best
assurance against noise interference is to install
an interposing relay in close proximity to the
MCD 200 soft starter.
• Why is it necessary to apply control voltage
before (or with) mains voltage?
There is a possibility the soft starter could arrive
at site with the internal bypass relays in “closed”
state. On first application of control voltage, the
bypass relays are commanded to open. If mains
voltage is applied without control voltage, this
step is missed, and the motor may start DOL
without warning (see Product Note for more
detail).
• What are the under- & over-frequency trip points
for MCD 200 soft starters?
The trip points are 40 Hz and 72 Hz. If the
frequency falls below 40 Hz or rises above 72
Hz, the soft starter will trip (x 6 Ready LED
flashes). These trip points are not adjustable.
A supply frequency trip will also occur if all three
phases from the mains supply are lost, or fall
below approximately 120 VAC while the soft
starter is running.
A supply frequency trip will occur if the line
contactor drops out during running.
• Will the motor start DOL if the start ramp of MCD
201 open loop soft starter is set to “full voltage”?
No, the MCD 201 will still provide a limited soft
start. The voltage is ramped up from 0 to 100%
in approximately 0.25 seconds.
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