Peter, I do not find your question specific enough: which standards, what fault(s), where in the world? Are you considering equipment connected only by domestic ac mains plugs or also hard-wired or connected using industrial plugs? It is certainly common for product safety standards, such as IEC 60950-1, to permit the branch protector to protect the power cord in the event of a phase to earth fault in the equipment, for example. The need to cater for a variety of possible time-current characteristics that also vary with rated current is why we have gone from a simple 1.5 times over-current protector (e.g. fuse or circuit breaker) rating with no time specified but a maximum of 25A in the first and second editions to the more complicated test conditions that we have in the third edition of IEC 60950 and the first edition of IEC 60950-1. Consider also that a building may be protected by fuses or circuit breakers. Both fuses and circuit breakers are typically available in a variety of time-current characteristics. The fuse standards in the USA are different >from those used in Europe: ditto for circuit breakers. At extremely high overload conditions the mechanical inertia of circuit breakers means that there is a minimum time below which they will not trip, irrespective of how high the current goes - this is not true of fuses. So what fuse or breaker were you thinking of using to guarantee that a fault in the equipment will always pull out the building over-current protective device ? Note also that EN 60950-1 has a Common Modification as compared to IEC 60950-1 in this regard (see 2.7.1). Richard Hughes
From: peter merguerian [mailto:[email protected]] Sent: 28 January 2003 19:54 To: [email protected] Subject: Circuit Breaker Tripping Dring Fault Tests Dear All, For safety, it is not clear from the standards whether the main branch circuit breaker tripping during fault conditions is an acceptable result. I see no reason why this should not be acceptable. What is your view? Some third party labs find it acceptable and others do not. Anyone can lead me to some inernational decisions regarding this issue? Thanks, Peter _____ Do you Yahoo!? Yahoo! Mail <http://rd.yahoo.com/mail/mailsig/*http://mailplus.yahoo.com> Plus - Powerful. Affordable. Sign up < ttp://rd.yahoo.com/mail/mailsig/*http://mailplus.yahoo.com> now
