Emergency Stop


Thread Starter


Hi all

I have small question about Emergency stop action.

Emergency stop shall go directly to MCC to stop the motor or is it ok route Emergency stop thru PLC to MCC??

Also, Emergency stops shall be only Hardwired? Can Emergency stop be defined at HMI?

I hope experts here can answer my question


Bob Peterson

If it is truly an emergency stop, it needs to be hard wired.

Sometimes pushbuttons or other controls labeled emergency stop really are not emergency stops, but just stops. I suspect they have acquired the label "emergency" to discourage the operators from using them as actuating them may have unpleasant consequences to the operation of the equipment or to the product.
hi Pandu,

for the first part its so important to know if this motor working within process application or just stand alone application. also can you explain what does mean hardware, still you have to have an I/o signal goes to specific controller (plc) to de-energize the motor. pls give us more info


Gerrit Jan Dreijer

> If it is truly an emergency stop, it needs to be hard wired.

Maybe in the US but not in the EU.
It's better the emergency stop circuit has minimum components to perform its function. i.e., stopping the machine at once in an emergency situation bypassing every other circuitry. Hence, it's better the circuit is hardwired and one way of accomplishing the function is to wire the `NC' (Normally closed) contact of the emergency stop switch in series in the path of main contactor's coil supply wiring.

A typical example is, you see a small fire or smoke or find a charring smell in an equipment or, someone's work clothing is getting caught in a fan blade or between a pulley and the belt and the situation demands the equipment be stopped immediately before something fatal or more dangerous consequence occurs.

Another example is, someone on a treadmill routine feeling giddiness and can not carry on further. The fall can be injurious or even fatal.

In such situations, one can not go through the routine procedures / interlocks before shutting down the equipment or look for the feeder at another location to switch off the power supply to the equipment. Situation demands immediate shut down.

Hence, do not wire it to the control wiring interlock through a PLC or relay logics. It should directly go to the feeder trip / MCC.
It is a good practice to put the Emergency stop circuit in a Normally-closed contact. This is to make sure that the wires from the E-stop button going to the actual actuator that stops the machine has no wire break. If you do it in a normally-open contact and for some reason there is some lose wires in the circuit, the E-stop won't work when you needed it.

Also try to do it both hard wired and through the PLC, meaning both will (try to) actuate your stopping mechanism.


Always worth noting, when an emergency stop is pressed, and then depressed the machine should not start up again. In my design's I always incorporate a reset push button in the MCC room. More thought must go into restarting the machine then.