Clause 5.4.9 of my copy of UL 1950 states that "During the tests of 5.4.4 c), 5.4.5, 5.4.6, 5.4.7 and 5.4.8:
- if a fire occurs it shall not propagate beyond the equipment; - the equipment shall not emit molten metal; - if a wire or a printed wiring board trace in the primary circuit opens, the gap is to be electrically shorted and the test continued until ultimate results occur. This applies to each occurrence; - if a trace in a secondary circuit is designed to intentionally open in a repeatable manner, the test is to be conducted three times to determine if the circuit does open repeatedly." If the standard allows a trace to open during component fault tests, the test engineer should not consider it an unacceptable result. Patty Elliot Qualcomm, Inc. San Diego, CA USA [email protected] At 11:12 PM 1/7/99 +0200, Peter Merguerian wrote: >To Rich, Doug and All Members, > >I just got clarification from UL that opening of a trace during >Overvoltage Tests is OK as long as unit passes either the Leakage >and Dielectric Tests. However, opening of a trace during >component abnormals would be considered an unacceptable result. > >Thank you everyone for all the input. > > >Date sent: Tue, 5 Jan 1999 16:08:51 -0800 (PST) >From: Rich Nute <[email protected]> >To: [email protected] >Subject: Re: UL1950 Overvoltage Tests >Copies to: [email protected] (Product Safety Technical >Committee) >Send reply to: Rich Nute <[email protected]> > >> >> >> Hi Doug: >> >> >> > Isn't this a variation of using the traces as a fusing element >> > instead of using a real fuse? >> >> Not necessarily. >> >> In Peter's situation, the test was that of the integrity >> of the insulation between the TNV circuit and the other >> circuits. >> >> So, if the "fused" trace did not bridge the insulation, >> then there should be no consideration that the trace was >> being used as a fuse. It is simply a failure, and a >> particular kind of failure -- open-circuit. >> >> Many, many fault-condition (abnormal) tests end up with an >> open circuit. We don't treat all component open-circuits >> as fuses. So, why should we treat an open trace as a fuse? >> >> It is unlikely that fusing of a trace will bridge a safety >> insulation. On the other hand, fusing of a transformer >> winding wire may be associated with enough heat to damage >> the solid safety insulation within the transformer! >> >> On the other hand, if the fusing of the trace should >> prevent an overheating situation (fire?), then the trace >> probably should be evaluated for its fusing action. >> >> So, one needs to understand the nature of the test in >> order to evaluate the results of the test to determine >> whether the opening of a trace is a fusing action as >> opposed to simply the end of a fault-condition test. >> >> >> Best wishes for the New Year, >> Rich >> >> >> >> ------------------------------------------------------------- >> Richard Nute Product Safety Engineer >> Hewlett-Packard Company Product Regulations Group >> AiO Division Tel : +1 619 655 3329 >> 16399 West Bernardo Drive FAX : +1 619 655 4979 >> San Diego, California 92127 e-mail: [email protected] >> ------------------------------------------------------------- >> >> >> >> >> >> --------- >> This message is coming from the emc-pstc discussion list. >> To cancel your subscription, send mail to [email protected] >> with the single line: "unsubscribe emc-pstc" (without the >> quotes). For help, send mail to [email protected], >> [email protected], [email protected], or >> [email protected] (the list administrators). >> > > >PETER S. MERGUERIAN >MANAGING DIRECTOR >PRODUCT TESTING DIVISION >I.T.L. (PRODUCT TESTING) LTD. >HACHAROSHET 26, P.O.B. 211 >OR YEHUDA 60251, ISRAEL > >TEL: 972-3-5339022 >FAX: 972-3-5339019 >E-MAIL: [email protected] >Visit our Website: http://www.itl.co.il > >--------- >This message is coming from the emc-pstc discussion list. >To cancel your subscription, send mail to [email protected] >with the single line: "unsubscribe emc-pstc" (without the >quotes). For help, send mail to [email protected], >[email protected], [email protected], or >[email protected] (the list administrators). >
