Ok, brain damaged after several long nights as a code monkey - did not finish my answer.
as you know, the last choice is delimited by "Where an overcurrent protective device is used, it shall be a fuse or a non-adjustable, non-autoreset, electromechanical device." Because electromechanical devices cannot meet the cycle (reliability) requirments of IEC60730, they are not allowed. As breakers age, there trip level and time-to trip may not always age gracefully. Also, there is the risk that an operator may attempt to hold the breaker closed during overload. In any case, UL60730-1A states DVD.4.1 A power limiting component - resistor, positive temperature coefficient THERMISTOR, diode, or the like - employed to limit the output of a power source to within the required current or power levels, or otherwise relied upon to comply with the performance requirements in Sub-clause DVD.6 shall have permanence and stability so as not to decrease its limiting capabilities. Among the factors considered when determining the acceptability of a power limiting component are: a) Effect of operating temperature, b) Electrical stress level, c) Effect of transient surges, d) Resistance to moisture, e) Endurance, f) Temperature change shock, and g) If appropriate, thermal runaway. R/S, Brian From: Brian O'Connell [mailto:[email protected]] Sent: Tuesday, June 17, 2008 6:50 AM To: 'Jim Eichner'; '[email protected]' Subject: RE: 60950-1:2006 clause 2.5 - Limited power sources Logic error - the requirements of cl 2.5 are connected by 'OR' logic. Note that one of the choices is "b) a linear or non-linear impedance limits the output in compliance with Table 2B. If a positive temperature coefficient device is used, it shall pass the tests specified in IEC60730-1, Clauses 15, 17, J.15 and J.17; or" Assuming that this is for a mains-isolated LPS output, we can say that this is not related to overcurrent protection for branch circuits, and will also assume that another overcurrent protective device is being used to satisfy NEC 240.10. If the above is true, then a PTC, that is certified as a current interrupt where the end-use meets its conditions of acceptability, should be acceptable if a short or overload meets the limits of table 2C. I have used 'auto-resetting' PTCs to meet the requirements of both UL60950-1 and UL1012, their use IS, in fact, allowed. But I have also 'encouraged' the designers to include other series impedances that will also provide ultimate current limits not dependent on the PTC. luck, Brian From: [email protected] [mailto:[email protected]]On Behalf Of Jim Eichner Sent: Tuesday, June 17, 2008 2:24 AM To: [email protected] Cc: Jim Eichner Subject: 60950-1:2006 clause 2.5 - Limited power sources If an overcurrent protective device is used, it is not allowed to be auto-resetting. Why? Just above this requirement is an allowance to use PTC's and they auto-reset, so why the bias against auto-reset breakers? Thanks, Jim Eichner, P.Eng. Compliance Engineering Manager Xantrex Technology Inc. e-mail: [email protected] web: www.xantrex.com - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
