RE: Creepage dist. for more than 1000V ?
I hesitate to remind you all, but if anyone has a problem interpreting the requirements of IEC 60950, there is the TC74 Chairman's Advisory Panel. Briefly, the procedure is as follows : Questions for interpretation should, as a minimum - define the problem, making reference to a specific subclause or subclauses of the Publication and, where appropriate,include a sketch; - provide an explanation of the actual situation that initiated the need for interpretation; and - be phrased, where possible, to permit a specific yes or no answer. Requests for interpretation of test results will not be considered by the Panel. Questions for interpretation should be submitted initially to the appropriate National Committee for TC74. Those that cannot be handled by the National Committee are forwarded to the Secretary of TC74. The Secretary of TC74 refers the Question to the Chairman of the Panel. ...and it goes on. I have personally had a request for interpretation answered, to the effect that : The unanimous Opinion of the Chairman's Advisory Panel is that the apparent difference represented by the words overbalance and tip over (in 4.1 stability requirements) is an editorial accident and that all three requirements are the same. Regards, John Crabb, Development Excellence (Product Safety) , NCR Financial Solutions Group Ltd., Kingsway West, Dundee, Scotland. DD2 3XX E-Mail :john.cr...@scotland.ncr.com Tel: +44 (0)1382-592289 (direct ). Fax +44 (0)1382-622243. VoicePlus 6-341-2289. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Creepage dist. for more than 1000V ?
95fbd8b0830ed511b7720002a51363f1319...@exw-ks.ks.lsil.com, Ehler, Kyle keh...@lsil.com inimitably wrote: Ah yes, the blissful aroma of hot tubes, ozone and fried flybacks..those were the days.. Didn't you have selenium rectifiers, too.? Inhaling selenium dioxide in small amounts can be good for throat infections, but don't overdose! -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk This message and its contents are not confidential, privileged or protected by law. Access is only authorised by the intended recipient - this means YOU! The contents may be disclosed to, or used by, anyone and stored or copied in any medium. If you are not the intended recipient, please advise the sender yesterday at the latest. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Creepage dist. for more than 1000V ?
sb695074@accusort.com, Terry Meck tjm...@accusort.com inimitably wrote: I don't recall the Sony but do recall the Philco and that Zenith held out with the `hand wired' chassis. ITT-KB went back to 'hand-wired' as a marketing point in 1963 (IIRC), because of overheating problems with the previous all-printed designs. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk This message and its contents are not confidential, privileged or protected by law. Access is only authorised by the intended recipient - this means YOU! The contents may be disclosed to, or used by, anyone and stored or copied in any medium. If you are not the intended recipient, please advise the sender yesterday at the latest. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Creepage dist. for more than 1000V ?
sb69402e@accusort.com, Terry Meck tjm...@accusort.com inimitably wrote: You can't change the facts. So yes! In the Middle to late 50's. :-) John Woodgate j...@jmwa.demon.co.uk 08/01/01 03:16PM sb67c5fe@accusort.com, Terry Meck tjm...@accusort.com inimitably wrote: I saw the first PCB show up in TVs, Would you care to put a date on that? Well, I asked because in Britain, Kolster-Brandes (part of ITT) TVs had printed boards (just part of the circuit, of course) from 1956. Snap? -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk This message and its contents are not confidential, privileged or protected by law. Access is only authorised by the intended recipient - this means YOU! The contents may be disclosed to, or used by, anyone and stored or copied in any medium. If you are not the intended recipient, please advise the sender yesterday at the latest. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
RE: Creepage dist. for more than 1000V ?
Ah, you guys have about 10/15 years on me... I remember the Motorola Quasar 'works in a drawer'. When they didnt work, they were hard to fix.. Zenith had the motto 'the quality goes in before the name goes on'. They really were pretty good. RCA had the best chassis, but the grounds always rattled loose on the corners of the pcb's. I was a genius at fixing these with a soldering gun -customers loved me, much to the disdain of the shop's $39.95 bench fee... ROUND CRT's (kinescope) 'nuff said. Curtis Mathis was a rebadged RCA chassis in a nice, expensive wood box (I cant recall the RCA chassis #...'105'?) I really hated those 'combo' sets with stereo --500lbs!! eight feet long and always in the basement w/fried flyback.. The worst TV's in North America were the 'packard-bell' ilk...that great tradition carried on in their pc's.. Admiral's were ok -as long as you didnt twiddle out the ferrite core thingy's... dog hair + vacuum tubes = fuzz w/glass bumps. dim bulbs..stinky tv..pops and snaps. crt 'brighteners' -sorry, but your pix toob is kaput, now..its just a BIG radio w/4 channels.. Globar resistor, or at least a shadow of where it WAS.. Ah yes, the blissful aroma of hot tubes, ozone and fried flybacks..those were the days.. I was sooo good that I retired after 10 months.. -kyle =:) -Original Message- From: Rich Nute [mailto:ri...@sdd.hp.com] Sent: Thursday, August 02, 2001 12:45 PM To: emc-p...@majordomo.ieee.org Subject: Re: Creepage dist. for more than 1000V ? Hi Terry: I don't recall the Sony but do recall the Philco and that Zenith held out with the `hand wired' chassis. Now that you mention it... I do indeed recall that campaign. But, I did not -- then -- realize the context. Today, looking back, that campaign was really quite absurd! But it worked! Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
RE: Creepage dist. for more than 1000V ?
Rich, Not really absurd given the quality of some of the board construction materials I saw in those early days. For one thing, the materials did not suffer heat well for very long (paper/phenolic?) - remember they were still using tubes or later a mix of tubes semi's. I also worked in TV shops during school and can remember thoroughly cooked PCB materials. Regards, Jack Xerox EMC -Original Message- From: Rich Nute [mailto:ri...@sdd.hp.com] Sent: Thursday, August 02, 2001 10:45 AM To: emc-p...@majordomo.ieee.org Subject: Re: Creepage dist. for more than 1000V ? Hi Terry: I don't recall the Sony but do recall the Philco and that Zenith held out with the `hand wired' chassis. Now that you mention it... I do indeed recall that campaign. But, I did not -- then -- realize the context. Today, looking back, that campaign was really quite absurd! But it worked! Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall, --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Creepage dist. for more than 1000V ?
Rich: The reason Zenith was using the `hand wired' promo was the `cold' and overheated PC boards especially the tube sockets that unsoldered themselves or when the trace separated from the board. This takes me back to the creapage point. I remember cutting away base board material, actually the carbon results, when that was the only solution other then scrapping the product. I also remember `hand wiring' repairs to PCAs and the customer wishing they had purchased a `hand wired' set. Growing pains of an industry that has been taken for granted for many years. But those experiences come in handy when I recommend to the system designer `remember to read the conditions of acceptability of the power supplies! What is the pollution Degree?' Terry Rich Nute ri...@sdd.hp.com 08/02/01 01:45PM Hi Terry: I don't recall the Sony but do recall the Philco and that Zenith held out with the `hand wired' chassis. Now that you mention it... I do indeed recall that campaign. But, I did not -- then -- realize the context. Today, looking back, that campaign was really quite absurd! But it worked! Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall, --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Creepage dist. for more than 1000V ?
Hi Terry: I don't recall the Sony but do recall the Philco and that Zenith held out with the `hand wired' chassis. Now that you mention it... I do indeed recall that campaign. But, I did not -- then -- realize the context. Today, looking back, that campaign was really quite absurd! But it worked! Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Creepage dist. for more than 1000V ?
Rich: My resolution when we go that far back is +/- 5 years minimum :-) :-) I don't recall the Sony but do recall the Philco and that Zenith held out with the `hand wired' chassis. Terry Rich Nute ri...@sdd.hp.com 08/02/01 12:38PM I saw the first PCB show up in TVs, Would you care to put a date on that? You can't change the facts. So yes! In the Middle to late 50's. :-) Having been a TV serviceman until 1960 (end of my college days), I saw no PCBs in USA TVs. I do recall PCBs in circa 1963 TVs. (Anyone remember the Sony tummy TV of the time?) :-) Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall, --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Creepage dist. for more than 1000V ?
I saw the first PCB show up in TVs, Would you care to put a date on that? You can't change the facts. So yes! In the Middle to late 50's. :-) Having been a TV serviceman until 1960 (end of my college days), I saw no PCBs in USA TVs. I do recall PCBs in circa 1963 TVs. (Anyone remember the Sony tummy TV of the time?) :-) Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Creepage dist. for more than 1000V ?
You can't change the facts. So yes! In the Middle to late 50's. :-) John Woodgate j...@jmwa.demon.co.uk 08/01/01 03:16PM sb67c5fe@accusort.com, Terry Meck tjm...@accusort.com inimitably wrote: I saw the first PCB show up in TVs, Would you care to put a date on that? -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk This message and its contents are not confidential, privileged or protected by law. Access is only authorised by the intended recipient - this means YOU! The contents may be disclosed to, or used by, anyone and stored or copied in any medium. If you are not the intended recipient, please advise the sender yesterday at the latest. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall, --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Creepage dist. for more than 1000V ?
sb67c5fe@accusort.com, Terry Meck tjm...@accusort.com inimitably wrote: I saw the first PCB show up in TVs, Would you care to put a date on that? -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk This message and its contents are not confidential, privileged or protected by law. Access is only authorised by the intended recipient - this means YOU! The contents may be disclosed to, or used by, anyone and stored or copied in any medium. If you are not the intended recipient, please advise the sender yesterday at the latest. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Creepage dist. for more than 1000V ?
Rich: As always I appreciated your eloquent explanation of the concept of the creapage requirement. Unfortunately experience has taught me long before your email. My question was based on the fact the standard does not SEEM to address the larger creapage distance 1000 volts. My reasoning could only conclude those writing the standard concluded the clearance issue would be just as critical as creapage 1000 volts. My recommendations have always ignored the minimum REQUIREMENT in this area because my nose recalls too many less then conservative designs burning up. I also recall an incident way back when I was wet behind the ears and still servicing TV (I saw the first PCB show up in TVs, How old I feel now). I opened the newspaper and saw a home of a customer burned due to the TV. This home was one I had used the vacuum cleaner in their TV every time I visited. Apparently I was too successful at my last visit and it was a long time since I had been there, no cleaning and I could picture the creapage disaster that happened. I was never absolutely sure of this since I was not a part of the post mortem. I seem to remember some one saying `All safety standards come from bad experiences.' or something like that. Right Rich? As always I enjoyed your detailed understanding. Best regards, Terry Rich Nute ri...@sdd.hp.com 07/31/01 01:59PM Hi Terry: I thought the lack of creapage spec. at 1000 V is that the dielectric strength of air would be less then the insulating material and surface accumulated contaminates. As a result the clearance distance would be the first to break down 1000 Volts. In general, the electric strength of air is orders of magnitude less than that of solid insulation. The distance between conductors on the surface of an insulator (e.g., a printed wiring board), must be based on the electric strength of air, not the solid insulation. In some applications, the surface of a solid insulation is subject to deposition of an unknown foreign matter (referred to in the standards as a pollution). Think of this pollution as a bread- crumb trail between the two conductors, that is, small pieces of matter separated by air. Consider the worst-case where the crumbs are metallic. These pieces of metal short out some of the air, thus redistributing the electric field (equipotential lines). At some point in the accumulation of foreign matter, the electric field between two adjacent crumbs becomes so great as to break down the air between the two crumbs. (An alternative theory is that the crumbs themselves dissipate power, glow, and change into a gas.) This micro-arc (or glowing) has a very high temperature, in the thousands of degrees C. While the energy is very small, the thermal energy can do microscopic damage to the surface of the solid insulation. For organic insulators, the damaged surface degrades to a microscopic carbon dot. Carbon, being the stuff resistors are made of, contributes to further redistribution of the electric field. And the process continues. Over a long period of time, a tree of carbon paths will form on the surface of the solid insulation. Eventually, the resistance tree will connect the two conductors, and a continuous leakage current will result. The resistive path dissipates power in the form of heat. This creates still more carbon, reducing the value of the resistance, and the leakage current goes up. And the power (and heat) disspated in the carbon path goes up. The process continues until a final catastrophic event destroys the solid insulation (and, hopefully, causes the circuit protection to operate). According to the researchers, this surface- insulation failure mechanism is mainly due to the working voltage across the insulation. (On the other hand, the through-insulation failure of solid and air insulation is mainly due to overvoltages, not the working voltage.) The values of distance along the surface of solid insulation (creepage distance) are based on working voltage. The values of distance through solid insulation and of distance through air insulation are based on expected overvoltages. The values of distance along the surface of solid insulation are not related to the values of distance for air insulation. As a general rule, the values for creepage distance exceed the value for clearance. When both are subjected to an overvoltage test, the clearance usually will break down rather than the creepage distance. However, this is not the intent of the requirements (because the clearance distances are minimums and could be much larger than the creepage distances). I'm afraid I cannot comment as to why there are no values for creepage above 1000 V rms. Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at:
Re: Creepage dist. for more than 1000V ?
Rich, Interesting info about how arcs form across PCBs, wish I had knew this a few years back. In this case I had a situation where PSUs were being taken down by fabric form ESD coats. The general non conductive cotton and polyester was settling between comports and an occasional, very conductive ESD nylon fiber would bridge between two different potentials. The Nylon fiber would conduct, vaporize from the massive current (this was happening in the primary boost circuit) and the heat ignite the cotton fibers. Leaving a nice cloud of ionized gas to carry a high current for sufficient duration to spectacularly blow a few components and take out he primary fuse. Took a long time to get the bottom of this failure mode, a lot of fault reproduction, much head scratching and a very handy high speed camera to watch what was occurring during those 10 ms. Moral of the story, very innocent looking this can seriously effect your creepage distance. Rich Nute wrote: Hi Terry: I thought the lack of creapage spec. at 1000 V is that the dielectric strength of air would be less then the insulating material and surface accumulated contaminates. As a result the clearance distance would be the first to break down 1000 Volts. In general, the electric strength of air is orders of magnitude less than that of solid insulation. The distance between conductors on the surface of an insulator (e.g., a printed wiring board), must be based on the electric strength of air, not the solid insulation. In some applications, the surface of a solid insulation is subject to deposition of an unknown foreign matter (referred to in the standards as a pollution). Think of this pollution as a bread- crumb trail between the two conductors, that is, small pieces of matter separated by air. Consider the worst-case where the crumbs are metallic. These pieces of metal short out some of the air, thus redistributing the electric field (equipotential lines). At some point in the accumulation of foreign matter, the electric field between two adjacent crumbs becomes so great as to break down the air between the two crumbs. (An alternative theory is that the crumbs themselves dissipate power, glow, and change into a gas.) This micro-arc (or glowing) has a very high temperature, in the thousands of degrees C. While the energy is very small, the thermal energy can do microscopic damage to the surface of the solid insulation. For organic insulators, the damaged surface degrades to a microscopic carbon dot. Carbon, being the stuff resistors are made of, contributes to further redistribution of the electric field. And the process continues. Over a long period of time, a tree of carbon paths will form on the surface of the solid insulation. Eventually, the resistance tree will connect the two conductors, and a continuous leakage current will result. The resistive path dissipates power in the form of heat. This creates still more carbon, reducing the value of the resistance, and the leakage current goes up. And the power (and heat) disspated in the carbon path goes up. The process continues until a final catastrophic event destroys the solid insulation (and, hopefully, causes the circuit protection to operate). According to the researchers, this surface- insulation failure mechanism is mainly due to the working voltage across the insulation. (On the other hand, the through-insulation failure of solid and air insulation is mainly due to overvoltages, not the working voltage.) The values of distance along the surface of solid insulation (creepage distance) are based on working voltage. The values of distance through solid insulation and of distance through air insulation are based on expected overvoltages. The values of distance along the surface of solid insulation are not related to the values of distance for air insulation. As a general rule, the values for creepage distance exceed the value for clearance. When both are subjected to an overvoltage test, the clearance usually will break down rather than the creepage distance. However, this is not the intent of the requirements (because the clearance distances are minimums and could be much larger than the creepage distances). I'm afraid I cannot comment as to why there are no values for creepage above 1000 V rms. Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute:
Re: Creepage dist. for more than 1000V ?
Terry Meck wrote: Hi Rich: I thought the lack of creapage spec. at 1000 V is that the dielectric strength of air would be less then the insulating material and surface accumulated contaminates. As a result the clearance distance would be the first to break down 1000 Volts. Am I wrong? Not really, but you might have a construction where the clearance isn't straight line through air. - Doug McKean --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Creepage dist. for more than 1000V ?
Hi Rich: I thought the lack of creapage spec. at 1000 V is that the dielectric strength of air would be less then the insulating material and surface accumulated contaminates. As a result the clearance distance would be the first to break down 1000 Volts. Am I wrong? Best regards, Terry J. Meck Senior Compliance/Test Engineer Accu-Sort Systems Inc. Rich Nute ri...@sdd.hp.com 07/30/01 03:42PM Hi Israel and John: I wonder how to specify creepage distance for Information Technology Equipment.Table 6 in UL1950 or EN60950 specifies minimum creepage of 10 mm for Working voltage = 1000 V, pollution degree 2, material group IIIb (basic insulation) linear Interpolation is permitted between nearest specified points. So how can one determine creepage distance for 1500 V, 2000 V ? Although it ought to be stated more explicitly, this means that you use the clearance tables for voltages for which creepage is not specified in Table 6. Hmm. Interesting. Here are the clearances and creepage distances as a function of voltage for basic insulation, pollution degree 2, material group IIIb: Voltage Table 3 Table 5 Table 6 ClearanceClearanceCreepage --- -- 50 2.0 mm 1.0 mm 1.2 mm 100 1.0 1.4 125 1.5 150 2.0 1.0 1.6 200 1.4 2.0 250 2.5 300 2.0 1.9 3.2 400 4.0 500 2.5 600 3.2 3.2 6.3 1000 4.2 4.210.0 2000 8.4 8.4 5000 17.5 17.5 Using John's interpretation, the creepage distance for 2000 V would be 8.4 mm. This is less than the creepage required for 1000 V. This is okay because the rule is that the creepage cannot be less than the required clearance. I would be happier if the rule said that, for voltages exceeding 1000, the creepage shall be not less than the clearance of Table 3 or 5, but not less than 10 mm. Using this rule, I would interpolate the creepage for 2000 volts using 1000 V/10 mm and 5000 V/17.5 mm. This would give me a creepage of 10 + 0.4*7.5 or 13 mm. Since the standard is silent on creepages for voltages exceeding 1000 V, there is no correct interpretation for determining the creepages. The most conservative interpretation is most likely to be accepted by most certification houses. The most conservative intepretation would be a curve based on the table data. The data is reasonably linear: creepage mm = 0.0097*V + 0.29 Using this equation, the creepage for 2000 V would be 19.7 mm. Creepages at some voltages are larger than clearances in order to minimize long-term surface degradation due to the value of working voltage. Studies of these effects have been published. In the above table, we see that, for primary circuits, creepage is less than clearance for voltages up to 200. Above 200 volts, creepage exceeds clearance. This suggests that for 2000 volts, the creepage should be larger than the 8.4 mm clearance. Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall, --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Creepage dist. for more than 1000V ?
000601c11881$36e04600$1e44d1d1@stella, Vygovsky, Yury edes...@inreach.com inimitably wrote: By interpolation the creepage for 1500v = 15mm or more, for 2000v=20mm or more. No, that would be extrapolation, and the standard doesn't say you can do that. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk This message and its contents are not confidential, privileged or protected by law. Access is only authorised by the intended recipient - this means YOU! The contents may be disclosed to, or used by, anyone and stored or copied in any medium. If you are not the intended recipient, please advise the sender yesterday at the latest. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Creepage dist. for more than 1000V ?
By interpolation the creepage for 1500v = 15mm or more, for 2000v=20mm or more. Yuriy Vygovskiy ENGINEERING DESIGN COMPLIANCE -Original Message- From: Israel Yeshurun israel_yeshu...@creoscitex.com To: 'emc-p...@majordomo.ieee.org' emc-p...@majordomo.ieee.org List-Post: emc-pstc@listserv.ieee.org Date: Sunday, July 29, 2001 2:13 PM Subject: Creepage dist. for more than 1000V ? Hello all ! I wonder how to specify creepage distance for Information Technology Equipment.Table 6 in UL1950 or EN60950 specifies minimum creepage of 10 mm for Working voltage = 1000 V, pollution degree 2, material group IIIb (basic insulation) linear Interpolation is permitted between nearest specified points. So how can one determine creepage distance for 1500 V, 2000 V ? Thanks in advance Israel Yeshurun Product Compliance. CreoScitex Corp. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall, --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Creepage dist. for more than 1000V ?
f49eb2d9f324d511bfc30008c7860394191...@csilex01.stil.scitex.com, Israel Yeshurun israel_yeshu...@creoscitex.com inimitably wrote: I wonder how to specify creepage distance for Information Technology Equipment.Table 6 in UL1950 or EN60950 specifies minimum creepage of 10 mm for Working voltage = 1000 V, pollution degree 2, material group IIIb (basic insulation) linear Interpolation is permitted between nearest specified points. So how can one determine creepage distance for 1500 V, 2000 V ? You are using the 1992 edition, but for new designs you should look at the 2000 edition. In the 1992 edition, look at Note 2 to Table 6, which refers you to the clearance tables 3 and 5 if the creepage is less than the clearance. Although it ought to be stated more explicitly, this means that you use the clearance tables for voltages for which creepage is not specified in Table 6. It isn't any more explicit in the 2000 edition, and I regret to say that it isn't any better in the final voting document for the next edition, either. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk This message and its contents are not confidential, privileged or protected by law. Access is only authorised by the intended recipient - this means YOU! The contents may be disclosed to, or used by, anyone and stored or copied in any medium. If you are not the intended recipient, please advise the sender yesterday at the latest. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
