I don't understand why electromechanical devices cannot be proven to have reliable cycle life. There are electromechanical devices tested for 6,000 cycles and 100,000 cycles commonly available, and there may be other classes with even higher cycle life. The standards all require that holding the breaker handle/button down after it has tripped must NOT allow the contacts to be held closed (so-called "trip-free" operation). The environmental and other stresses listed in your items a) to g) all seem to me to be something that a thermal breaker designer could design for.
Take for example a simple bimetallic circuit protector. I can't imagine such a device having a problem with any of this, except perhaps if the thermal expansion properties of either of the two metals changes too much during the cycling required by the standard. Is that the issue? The reason for my enquiry is standards committee work. We are importing this Limited Power Sources section, and it doesn't seem right to not allow auto-reset electro-mechanical devices. At the very least, we should allow them with a condition that they comply with a relevant standard that tests them for adequate cycle life (perhaps one of the 60730 series, but I'm sure there are more relevant standards for breakers and protectors that are electro-mechanical). Comments? Thanks as always for the forum's help. Jim Eichner, P.Eng. Compliance Engineering Manager Xantrex Technology Inc. e-mail: [email protected] web: www.xantrex.com Confidentiality Notice: This email message, including any attachments, is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message. From: Brian O'Connell [mailto:[email protected]] Sent: Tuesday, June 17, 2008 7:08 AM To: Jim Eichner; [email protected] Subject: RE: 60950-1:2006 clause 2.5 - Limited power sources 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. 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