Since this shutdown method might be considered normal operation, have you considered the consequences of rating your wiring, switches, thermal contactor etc. for the short circuit current capacity? A non-autoreset thermal switch (thermal fuse) would be a much better solution. Bob Johnson ITE Safety
Kunde, Brian wrote: > Instead of shorting the AC Mains, have you considered using a breaker > with a trip coil? We used one in a product where as a safety measure, if > something bad happened, we wanted to cut power to the entire machine. > All we had to do is short out a set of contacts which powered up the > trip coil to trip the mains breaker and all power was shut down. > > Going a different way, in my shop class in High School there were these > boxes with big red buttons hanging from cords from the ceiling all over > the shop. If you pushed any one of the red buttons, the power to the > entire shop would go off shutting down all the machines. Someone said > that when you pushed the red buttons, that it shorted out the AC and > popped the breaker for the entire room. Is that really how that was > done? > > Yet another story from my past. I know an electrician who if he is > going to work on a receptacle, he just takes a piece of wire and shoves > it in the receptacle to deliberately pop the circuit breaker. He says it > is faster than switching the breakers off and on one at a time till you > find the right one. That can't be good for the breaker, right? > > The other Brian. > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On Behalf Of Don Gies > Sent: Thursday, October 05, 2006 3:17 PM > To: [email protected]; [email protected] > Subject: RE: shorting the mains prohibited - Help > > Gregory, > > You should recommend thermal overtemp cutouts in each power lead (if AC > mains) that open upon overtemp rather than closing upon overtemp, with > reference to IEC 60950-1, Clause 4.3.7 (Heating elements in earthed > equipment). > > Shorting the mains is probably going to annoy someone, if not your > safety certification engineer. > > We once did have a small dc secondary heater circuit with an overtemp > device that closed upon overtemp. Doing so shorted out the dc supply, > thereby opening a 7 A fuse in front of the overtemp device. I don't > remember exactly the reason for this (maybe we couldn't find a > Recognized dc thermostat that opened), but the design was OK'ed by our > NRTL engineer. > > Regards, > > Don Gies, N.C.E > Senior Product Compliance Engineer > Lucent Technologies > Holmdel, NJ 07733 USA > > -----Original Message----- > From: Gregory H. McClure [mailto:[email protected]] > Sent: Thursday, October 05, 2006 12:25 PM > To: [email protected] > Subject: shorting the mains prohibited - Help > > Gentlemen, > > I need your collective memory. > > I have an engineer that wishes to design a protection mechanism to apply > a short circuit across the mains in order to open a protection device > upstream to stop an over-heating fault. The protection device would be > in the product, we are not talking about depending on the protection in > the service panel. I will not let them go there. > > I remember somewhere in the past that one of the standards, or perhaps a > country deviation, specifically forbid shorting the mains as a means of > protection but I cannot find it. I think it is from the era when we were > using IEC 380 or 435 and UL 478 but I am not sure. > > Can someone out there point me to the standard and clause? or perhaps > the deviation or an OSM decision? > > I am looking for all of the arguments against this practice I can pull > together because I do not feel it is sound. It is one thing to crowbar > the output of a power supply to protect an expensive logic board from a > power supply over-voltage failure. It is quite another to short the > mains input. > > Many thanks, > > Gregory H. McClure > Lexmark Product Safety > 859 232 3240 office > 859 232 6882 fax > > Confidentiality Notice: > This e-mail message, including any attachment, is for the sole use of > the intended recipient(s) and may contain confidential information. Any > unauthorized review, use, disclosure or distribution is strictly > prohibited. If you are not the intended recipient, please contact the > sender, by e-mail, and destroy all copies of the original message. > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. 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