Peter, Following on from Nick's response, he is correct in stating that the device should be easily actuated. In some jurisdictions, like Ontario, Canada where I am located, the regulations go on to say that the emergency stop devices should be located "within easy reach" of the operator when they are in the "normal operating position", in other words, at the intended work stations. This would not cover the situation that you are describing, since the machine is in a service mode, not normal operating mode.
To cover this condition, my first recommendation is to carry out a job hazard analysis, basically a risk assessment, of the work that the service operator is expected to do. Include specific conditions where power may be required on the equipment for fault-finding or other diagnostic activities. Once the hazards are identified and the risk analyzed, the next question to address is "Will provision of an emergency stop device provide the operator with the opportunity to avoid or limit the harm that could occur?" If the answer is YES, only then would I consider adding the emergency stop. It might be worthwhile looking at using a pendant style of device, particularly if the service operator will need to be able to jog the equipment. If there are no conditions where power would be required during service, then the use of lockout procedures and suitably located energy isolating devices is the best solution. By the way, it is important to understand that emergency stop systems are NOT safeguarding devices, which is why they can have lower control reliability requirements than safeguarding systems. They are complementary protective systems. The difference is this: a safeguarding device operates automatically, without any intentional act on the part of the person being protected. For example, a pressure relief valve is a safeguarding device because it will open automatically in the event that the pressure behind it exceeds its relief pressure. Likewise, a light curtain will act to stop the protected equipment when the field is breached without the person breaching the field doing anything intentional to stop the equipment. An emergency stop device must be intentionally activated by someone in order for anything to happen. Lockout of energy sources is preferred over safeguarding systems which are preferred over complementary protective devices. I'm available to discuss this offline if you need more information. -- Doug Nix, A.Sc.T. IEEE PSES Kitchener-Waterloo Section, Ontario, Canada d...@ieee.org mobile (519) 729-5704 fax (519) 653-1318 Find me LinkedIn at http://www.linkedin.com/in/dougnix On Aug 28, 2008, at 16:15, Nick Williams wrote: > You need to refer to EN ISO 13850 (which recently replaced EN 418). > Clause 4.4.1 states "The emergency stop device shall be designed to > be easily actuated by the operator and others who could need to > actuate it." In this context "the emergency stop device" should be > taken to mean the complete e-stop system, not just a particular > actuator. > > It's perfectly acceptable to daisy-chain emergency stop devices so > long as this does not reduce the reliability of the system (which is > won't if it's properly designed). Of course, NO contacts will need > to be in series and NC contacts will need to be in parallel. In > practice, most of the E-stop systems I have seen use two NC contacts. > > Nick. > > > > At 21:43 +0200 28/8/08, Peter wrote: >> Date: Thu, 28 Aug 2008 21:43:48 +0200 >> MIME-Version: 1.0 >> Content-Type: text/html >> >> Hi experts, >> >> I have a question about requirements for emergency switches used in >> machinery placed on market in EU. >> The machine complies to MD by compliance with amongst others EN >> 60204-1:2006 and has a full compliant emergency switch installed >> for USERS easy activation during normal use. >> >> Now my question is i have no where seen a requirement that another >> emergency switch should be available for SERVICE personel on say >> the back side or other place of the machine, as he/she might not >> have easy access during a service situation. The machine is not >> very large but a service person might not be able to reach the >> normal users switch when working on the back f.ex. >> >> Can anyone point out a requirement in EN 60204-1 or any other MD >> related standard that states the need for this ? >> The service person can of course disrupt the power using the main >> safety switch off device (lockable), and further he is expected to >> be somewhat more aware of dangers related to his job. >> >> Another question, is it allowed to add several emergency switches >> in parallel with the existing if wanted (currently it has one NC >> and one NO contact connected through a safety relay), but it would >> be possible to add screw terminals for further expansion (limited >> only by relays capacity) if needed. >> >> Hopefully above makes somewhat sence and a machinery experts likes >> to comment on this, have a nice day. >> >> Best regards >> Peter >> > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. Website: http://www.ieee-pses.org/ > > To post a message to the list, send your e-mail to emc-p...@ieee.org > > Instructions: http://listserv.ieee.org/request/user-guide.html > > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > > Scott Douglas emcp...@ptcnh.net > Mike Cantwell mcantw...@ieee.org > > For policy questions, send mail to: > > Jim Bacher: j.bac...@ieee.org > David Heald: emc-p...@daveheald.com > > All emc-pstc postings are archived and searchable on the web at: > > http://www.ieeecommunities.org/emc-pstc - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.org Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
