Emergency Stop Relay

Hi Everybody

Could you please clarify the following:

For Emergency Stop Relays, during a power cut and restore, should the relay be reset or this does not affect the system.

My point is that during a power cut/restore, the system should resume to work without any manual intervention/reset except that when the Emergency stop is pressed and upon release of the E/stop, a manual reset should be performed to make the circuit healthy.

Does the Emergency stop relay operate like this.

Thanks

http://www.plctalk.net/qanda/showthread.php?t=69246

http://www.plctalk.net/qanda/showthread.php?t=749

http://www.plctalk.net/qanda/showthread.php?t=44309

http://www.plctalk.net/qanda/showthread.php?t=7932

99% of the time, any automated system should never restart after a power outage, I'm talking manufacturing systems not self contained simple processes etc that can restart Al lot of the time.

Safety relays will drop out on power loss, requiring user intervention to reset.

("should the relay be reset?") You state.
Speaking purely of E-stops here following a plant "power cut/restore",
In my experience. it is not required to "reset the E-stops."

As to the question of whether or not a machine, motor or device is to power up immediately following said power fail or require manual action to restart, my experience says this is not an issue concerning an Emergency stop button or an emergency stop relay, but an issue of "2 or 3 wire control" wiring AND OR PLC Logic and/ or Power Up Handler Programming and "output state upon power up" configurartion.
As to purely control wiring; you are most likely aware that, 2 wire controls are like an "off-on" which will resume last state upon power returning and 3 wire controls are like a "start-stop" which WILL require operator input to restart after power fail then return.

http://www.plctalk.net/qanda/showthread.php?t=60476
discusses concepts surrounding Load states upon power up.
The above is my humble 2 cents,
Regards

To be clear, in my experience, an E-Stop is a specialized, (i.e... Red/ Clearly labelled and required to be located near the equipment) normally closed pushbutton that de-energizes the controller or feeds a relay that de-energizes the controller of a machine, motor or device INDEPENDENT of PLC control.
Kill it now! Someone is IN the machine!
I see debate in the thread I posted as to whether a VFD should be allowed to "stay powered" to brake a machine when an E-stop is pressed. I have rambled enough and will stay out of that.
Regards

My point is that during a power cut/restore, the system should resume to work without any manual intervention/reset...

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In the majority of cases, the system should NOT resume work without manual intervention. Most moving equipment can be dangerous if it starts suddenly and unexpectedly. But this system restarting may not be controlled by the Emergency Stop relay. The Emergency Stop relay should only activate during an emergency, not during a power outage.

Lancie1 said:

In the majority of cases, the system should NOT resume work without manual intervention. Most moving equipment can be dangerous if it starts suddenly and unexpectedly. But this system restarting may not be controlled by the Emergency Stop relay. The Emergency Stop relay should only activate during an emergency, not during a power outage.

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I've not come across an E. Stop relay that works like this though, all the ones I've used will need resetting after a power outage. Some of the Schneider ones actually work by removing power to the relay.

The rest I agree, in fact it is in the relevant EU standard that a system must not restart after an E. Stop without manual intervention.

The system not restarting is a function of the control design, not the Emergency Stop relay. We were doing that function a hyndred years before Emergency Stop relays were invented. That E-Stop relay may reset during a power outage, but that is not its main function.

As to purely control wiring; you are most likely aware that, 2 wire controls are like an "off-on" which will resume last state upon power returning ...

Click to expand...

Having worked as an electrician, I know what you mean by 2-wire controls, but there are ways to use 2 wires (with a PLC or an alternator relay - Allen Bradley 700-HTA) so that the control circuit does not resume the last state upon power returning. On example is by using a momentary Start/Stop pushbutton (press once to Start, press again to Stop). If you use non-retentive contacts in the PLC for the alternator logic, then this 2-wire control acts like 3-wire controls would. So defining control circuits by the number of wires used may not completely define the situation.

Lancie1 said:

You still missed the point. The system not restarting is a function of the control design, not the Emergency Stop relay. We were doing that function long before Emergency Stop relays were invented. That E-Stop relay may reset during a power outage, but that is not its main function.

Click to expand...

Yes of course manual restart predates E.Stop relays and is relevant to non safety critical control systems too. But then the OP asked this:

a_rishi said:

...My point is that during a power cut/restore, the system should resume to work without any manual intervention/reset except that when the Emergency stop is pressed and upon release of the E/stop, a manual reset should be performed to make the circuit healthy.

Does the Emergency stop relay operate like this...

Click to expand...

In reality most E. Stop relays will not operate the way he seems to want them to operate i.e. they will need resetting after loss of power. I assumed, perhaps wrongly, he was after some practical information.

good point

well taken

In reality most E. Stop relays will not operate the way he seems to want them to operate i.e. they will need resetting after loss of power.

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Read closely to what A-Rishi said. The word EXCEPT changes the meaning to the opposite: "...except that when the Emergency stop is pressed and upon release of the E/stop, a manual reset should be performed to make the circuit healthy".

That sounds like exactly the way the typical Emergency Stop relay operates. In other words, he wants the equipment not able to restart until the Estop is reset. But that function should also be done by proper design of the control logic. The emergency stop relay should be the last resort. Depending on the Estop to correct poor control design is not smart. Unfortunately there is a lot of that going on.

Lancie1 said:

Read closely to what A-Rishi said. The word EXCEPT changes the meaning to the opposite: "...except that when the Emergency stop is pressed and upon release of the E/stop, a manual reset should be performed to make the circuit healthy".

That sounds like exactly the way the typical Emergency Stop relay operates. In other words, he wants the equipment not able to restart until the Estop is reset.

Click to expand...

ehh, no. He wants the equipment to restart automatically after power loss... except when a estop-button is actually pressed.

Anyway. what about risk assessment and regulations? the real questions asked was, may a system restart automatically without user actions.