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]>
