Eric. There are places in a circuit where film resistors are required by UL, such as where they bridge insulation. Ordinary carbon resistors are unacceptable in these cases - at least in the categories I usually work in. So film resistors are not considered to fault in a shorted state. As for caps and diodes you must make that decision based upon what the result of the fault will be. If an unlikely fault (short or open) will be something that can result in a hazard - within the meaning of the applicable standard - then it should be considered and provision made in the design to prevent the unacceptable increased risk. Sorry this is not such a clear cut answer but diodes and capacitors can fail in both shorted and open states, so a certain amount of circuit analysis is necessary Approved X, Y, Antenna coupling caps, & Antenna bypass caps are not shorted during fault testing - at least in the categories I ordinarily work with. Components in low voltage circuits are not investigated (for safety) when the available power is below certain limits. Those limits will be given in the standard applicable to the product. Regards, Lou Aiken, LaMer LLC 27109 Palmetto Drive Orange Beach, AL 36561 USA tel ++ 1 251 981 6786 fax ++ 1 251 981 3054 Cell ++ 1 251 979 4648
----- Original Message ----- From: Van Compernolle, Eric <mailto:[email protected]> To: '[email protected] ' Sent: Thursday, October 23, 2003 9:40 AM Subject: Fault condition test UL 60950 Dear all, For the fault condition test ( single fault) you have to consider the risk on an open or short of a component. My question is the following: do we have to consider both a short and an open of a (film) resistor? Normally I should think that the only way that a fault can occur on such a resistor is an open. Do we have to consider also a short? The same question for a capacitor ( normal fault condition: short?) and diode (normal fault condition: short?). best regards, Van Compernolle Eric Reliability Manager Barco Projection System Noordlaan 5 Industriezone B-8520 Kuurne Belgium Tel. +32(0)56 36 82 11 Fax.+32(0)56 36 83 55 E-mail: [email protected] - - - - - - - DISCLAIMER - - - - - - - - Unless indicated otherwise, the information contained in this message is privileged and confidential, and is intended only for the use of the addressee(s) named above and others who have been specifically authorized to receive it. If you are not the intended recipient, you are hereby notified that any dissemination, distribution or copying of this message and/or attachments is strictly prohibited. The company accepts no liability for any damage caused by any virus transmitted by this email. Furthermore, the company does not warrant a proper and complete transmission of this information, nor does it accept liability for any delays. If you have received this message in error, please contact the sender and delete the message. Thank you.
