Emergency Stop Circuits and controls


Instrument (andheri)

In my opinion, an Emergency Stop should be accompanied by an audio / visual indication using perhaps a hooter and a beacon especially in a noisy shop floor environement or when large areas are involved. This is necessary so that the others
concerned are aware that some emergency exists. A normal operational stop does not require such indication.

Any emergency stop system should be tested at fixed intervals and this testing should be documented. After all Fire Drills are mandatory in many places? So why should Emergency Stops be
treated differently? Similarly, nobody would sound the fire alarm to announce the end of the day's work, although both may result in the employees leaving the building. So the normal operational stop and Emergency Stop functions should be segregated whenever practical.

Even in chemical plants, though the complete closing of an Emergency Shutdown Valve for testing may not be possible, it is still possible to design a system for 'Partial' Movement of the
valve to test the circuit.

Operating a switch once a month should not wear it out very much. I have known switches to malfunction just because they were not used.


Michael, start with dictionary definition of "emergency". Then embellish with definitions from IEEE Std 100-1992 "The IEEE Standard Dictionary of
Electrical and Electronics terms".

Phil Corso, PE
Trip-A-Larm Corp
To List members:
In answer to those requesting additional information on the article referenced in my Feb 22 Email "To E-Stop or not to E-stop"

The article entitled "e-stop" was authored by:

Tim Park, Product Manager
Electronic Brakes Division
TB Wood's Inc.
Chambersburg, PA

His article covered rotating machinery braking systems. However, he intelligently addressed the difference between "normal" stop and "emergency" action. For the former, time of response is unimportant, while for the latter, fast response is mandatory. This philosophy can be easily extrapolated to cover process SIS/ESD's.

As an example, taking a steam user "offline" doesn't require "slam-bam" action of its inlet valve. Instead, ramp the valve closed... unless a
potential damaging problem has occurred (eg, ruptured tube, lubricant loss, hi-vibration, etc). Then use the "slam-bam" plan!

Mr. Park's article was presented in the Magazine "PTdesign". Their web address is:


Phil Corso, PE
Trip-A-Larm Corp
I don't know of a specific regulation that requires a seperate stop button from the E-stop, I bet that an industrial lawyer could tell you right away.
Whilst not a direct answer to Anthony Kerstens' original question, I recently noticed the following statement in an Allen-Bradley "white paper" entitled "Emergency Stop Push Buttons" (Publication 800-WP008A-EN-P - May 2003), available in PDF format on the Web:


Mechanical Life

One of the more interesting parts of the European standards is the mechanical life requirements. Emergency stop push buttons are only required to be tested to 6,050 operations. This implies that emergency stop push buttons are not meant for everyday use. They are only to be used in emergencies.


I assume the above quote is referring to EN 418: 1992 and/or EN/IEC609457-5-5: 1998.

I hope this is of some help.

W.J. Hill
Airport Baggage Handling and Screening Specialist
Independent Consultant
By either NEC code and/or OHSHA regulation. An E-STOP must remove all electrical control of rotating equipment. This is why an E-STOP can cause severe damage, it is an uncontrolled stop, all regeneration of power "electric braking" is disabled, due to manditory opening of motor contacts.

Thus, a very sinple way to test an E-STOP system regularly is to test duing "OFF RUN" hours, when no physical damage can occur. Hit the E-STOP and check for power loss when no equipment is running.
Anthony... overlooking the fact your question was raised many, many years ago, are you still interested in a simple logic-circuit to implement the correct shutdown sequence regardless of the operator's contrary procedure?

Regards, Phil Corso (cepsicon [at] aol [dot] com)
Something that you might try to discourage the practice of hitting the e-stop button is to place an irritation such as a horn or strobe near the control desk that is initiated by the e-stop and has to be silenced or acknowledged in some way.