Individually Isolated Outputs


Thread Starter

Pascal Poirier

Hi everyone,

I would like to have your opinion about the use of individually isolated outputs in a PLC application. Should i use it for motor control? even if the motors are all in the same MCC?

Also, what are the good practices for emergency stop on those motors? Since the control voltage comes from each starter, the MCR has to interrupt
each output individually, requiring one set of contact for each. How can i avoid a hard relay panel inside a PLC panel?

Thank you for any comment...

Pascal Poirier
[email protected]

Blunier, Mark

Since each starter has its own control voltage transformer, use isolated inputs and outputs. This avoids setting up ground loops. As far as emergency stops, run the output in series with the E-stop, to the starter. Set the PLC up to latch the output on, when it has the auxillary
contact showing that the motor is running.

Mark Blunier
Any opinions expressed in this message are not necessarily those of the
If I understand your application, the normal approach is all outputs that require E-Stop integrity is to have these on a separate power supply and the MCR merely deenergizes this power supply effectively deactivating these outputs.
For the e-stop, use a shunt-trip main breaker in the MCC. A N.O. contact on your e-stop pushbutton will open the main breaker. Very effective and simple.

Al Boake P.E.