how to connect an emergency stop to a 3phase motor

[bob1]

I understand the concept(I think) but would like to have some input on this please,
when the e/stop is depressed it brakes the line hence cutting power,but when twisted it restores power
as the machine must be stopped totally by the e-stop im assuming I would have to connect across the contactors to de-energise them after pressing e-stop requiring a full system re-start


now.....how do i achieve that?
many thanks in advance,to any that take the time to reply

 

[Lectrician]

In series with red stop bottom om contactor Simple.

Dont wire it to any of the supply phases etc - insert it in the control cct.

 

[lazygit]

The best way would be to use a safety relay, try searching Farnell or RS components for one. If you interupt the coil of the contactor using the e-stop, you may have issues about automatic startup when the e-stop is reset.
However one way of fixing this issue is by placing the e-stop in series with a momentary start button for the contactor. Then have a spare set of normally-open contacts from the contactor across the start button.
This will latch the relay when you press the button, then when the estop is pressed, it will not resume untill the start button is pressed again.
If that makes any sense

 

[Taylortwocities]

This might help. Its 115v but the same wiring.

http://support.automationdirect.com/docs/an-mc-004.pdf

 

[Lectrician]

If you interupt the coil of the contactor using the e-stop, you may have issues about automatic startup when the e-stop is reset.

A DOL or Stardelta starter will usually be setup in a way that the green button starts (momentary push) and the red stops. Interupting the control cct will stop the machine, and the machine will not start again until the green button has been pressed.

Bypassing the green button to make the machine constantly live is very bad practice as there is then no undervoltage release provided.

 

[lazygit]

Bypassing the green button to make the machine constantly live is very bad practice as there is then no undervoltage release provided.

All I was trying to do was describe the circuit arrangement as illustrated in Taylowocities link.

 

[GaryMo]

If you interupt the coil of the contactor using the e-stop, you may have issues about automatic startup when the e-stop is reset.
However one way of fixing this issue...............

The issue wouldn't need fixing if an emergency stop button was installed correctly.

 

[ricicle]

Consideration is also required as to what is required of the emergency stop.

-Is it ok for the motor to just coast to a stop or is there a requirement for a brake

-Is there an invertor or the like which can be used to do the controlled stop and then the power needs removing from the drive after this has occured

-If the system needs to be fail-safe then the use of a safety relay is recommended

Just a few thoughts................................

 

[Spark123]

Yeah, some emergency stops start a DC injsection sequence which locks the 3 phase motor causing it to stop almost instantly. Commonly used on things like lathes and drills.

OP, what application is this for? In a DOL (direct on line) When you press the green button the contactor should energize pulling in a retaining contact. Pressing any stop button or another N/C item installed in series in the control circuit such as an overload will interrupt the supply to the contactor and it should drop out breaking the retaining contact.

 

[briwire]

We need to know the application so we can assess which type of safety circuit is required.

If it is something, say an extract fan, it still needs a starter (box containing a contactor, overload and having a green and red start and stop buttons. This ensures that if the power fails, the motor won't start once the power is restored. Its green button will have to be pressed manually. An emergency stop button is wired in series with the red stop button, as stated previously.

Other applications with more serious consequences may require safety relays, double pole emergency stops, motion detecting units, the list is endless.

 

[ricicle]

We need to know the application so we can assess which type of safety circuit is required.

If it is something, say an extract fan, it still needs a starter (box containing a contactor, overload and having a green and red start and stop buttons. This ensures that if the power fails, the motor won't start once the power is restored. Its green button will have to be pressed manually. An emergency stop button is wired in series with the red stop button, as stated previously.

Other applications with more serious consequences may require safety relays, double pole emergency stops, motion detecting units, the list is endless.

Not all motors require overloads (<370W don't and some safety applications)

Not all motors have to stay de-energised after a power failure if there would be greater danger if they did not automatically restart or if there is no danger if they did (eg submersed sewage pumps)
Warning signs need to be fitted so it is made known that there is automatically starting machinery.