I had a very similar situation. Are you using a C&K or Omron switch? I also remember seeing the switch and thinking it looks like the door light switch from an old refrigerator. I have a very similar-looking switch in my home oil furnace (which is from the 1980s)
What we did was put the switch inside a little metal enclosure with a small hole on the top. The panel then had a small metal protrusion which reached inside the hole, this way the test finger could never actuate the switch. You could try to take your designer's argument to your NRTL, but I doubt they will accept it; I think the point is not that someone's finger slips onto the switch accidentally and activates it, but rather - a service person wants to see if the product he just worked on will start up and so pushes in the interlock to see if what he fixed/replaced worked. -Ken On Tue, Jun 10, 2014 at 11:39 PM, Nyffenegger, Dave < [email protected]> wrote: > Hi folks, > > I'm reviewing a design for some medium duty office/business equipment > which handles mail and is subject to the Machinery and Low Voltage > Directives i.e. EN 60950-1 and EN 60204-1. The design is using an > interlock switch which I think is more suitable for turning the light > on/off in a refrigerator. The switch is in the secondary low voltage > circuit to operate the main contactor coils. It's only rated for 50K min > operations (electrical) and is approved to UL 1054 and VDE EN 61058-1. > The electrical specs are fine for the application. I'm not familiar with > these standards so one question is if those standards in anyway qualify or > disqualify (by using the switch in a way not intended) the switch for use > as a safety interlock. > > I thought I read in one of the safety standards that interlock switches > should be designed/rated to last the lifetime of the equipment (based on > some estimate of number of operations in application). But I haven't been > able to find that. Does that sound familiar to anyone? My estimate is > that 50K operations is much lower than the number of operations over the > lifetime of the equipment. > > A similar older switch is only rated by the manufacturer for 6K > operations. EN 60950 2.8.7 basically requires a minimum of 10K operations > the way I read it. Am I right in thinking the 6K switch would not be > suitable for interlock usage regardless of other aspects? > > These switches have plungers that can be easily finger operated once the > guards are opened. EN 60950-1 says that interlocks must be designed to > prevent inadvertent reactivation and that the ability to operate the > interlock with a test finger is considered likely to cause inadvertent > reactivation of the hazard. The argument from the designer with this > switch is that once the guard/interlock is open, reclosing the interlock by > itself will not re-energize the protected circuit and therefore there is no > inadvertent reactivation. This is because the control circuit requires > operation of another start switch in order to energize. This assumes there > is no concurrent failure of the control circuit while the interlock is > being manually overridden, one person can't operate/reach the start switch > and override the interlock at the same time, and no second person operating > the start switch while someone is overriding the interlock. My question is > if this argument actually holds with! > out violating the EN 60950 requirement. > > thanks > > David P. Nyffenegger, PMP, SM-IEEE > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. To post a message to the list, send your e-mail to < > [email protected]> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.org/ > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe) > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <[email protected]> > Mike Cantwell <[email protected]> > > For policy questions, send mail to: > Jim Bacher: <[email protected]> > David Heald: <[email protected]> > - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
