Jim, It seems that some of the "offshore" manufactured cords are molded from melted Hershey bars! I am always very careful who I buy my cords from.
Scott Lacey -----Original Message----- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of Jim Eichner Sent: Thursday, October 25, 2001 3:40 PM Cc: emc-p...@majordomo.ieee.org Subject: RE: skinny power cords. Thanks Rich: I suspect you're right. Isn't that mechanism exactly what the tracking index tests are meant to address? I thought that any UL-approved wiring device like this would have a material that is designed to resist tracking, hence my speculation that contamination might be involved. I guess there are a few more comments to be made here... 1. From what I know, the tracking index tests are horribly non-repeatable and are therefore somewhat meaningless. 2. The standards for plug caps and for multi-taps may not refer to UL746 and may not have any of their own requirements for tracking index of insulation. 3. We could take this as evidence that even compliance with the tracking index requirements doesn't prevent carbonization of the material where there's a high temperature heat source involved. There are lots of people who unplug anything they are not actively using. I guess it's not such a paranoid practice! Regards, Jim Eichner, P.Eng. Manager, Engineering Services Xantrex Technology Inc. Mobile Power web: www.xantrex.com <http://www.xantrex.com> Any opinions expressed are those of my invisible friend, who really exists. Honest. -----Original Message----- From: Rich Nute [mailto:ri...@sdd.hp.com] Sent: Thursday, October 25, 2001 12:14 PM To: jim.eich...@xantrex.com Cc: emc-p...@majordomo.ieee.org Subject: Re: skinny power cords. Hi Jim: > I'm curious: given that North American plug blades are >1/2" apart, there > must have been substantial contamination to aid in 120Vac jumping that far > (arcing). Did you identify any sort of contamination or moisture? I don't believe contamination is a significant factor in events such as this one. I believe such events start with a loose connection between the plug and the socket (or between the wire and the socket parts). A loose connection means that the contact area is relatively small. In turn, this means high current density at the point of contact. The smaller the contact area, the greater the resistance of the contact. The smaller the contact area, the greater the current density at the point of contact. These two factors contribute to heating of the two parts, the plug blade and the socket. Heating tends to reduce the "springiness" of the socket part, and of the connection between the supply wire and the socket (because they are thermally connected). The heating also tends to degrade the surface of the insulating material in which the conductors are mounted. Heating also enhances oxidation of the plating on the parts, which further increases the resistance of the connections. If the plug-connected appliance is "ON," arcing can occur as the parts expand due to heating and make various intermittant connections. Arc temperatures are very high, and can "burn" the surface of nearby insulating materials via radiation. As the surface degrades, leakages occur across the surfaces. At this point, whether or not the appliance is on or even connected is not a factor. There is a current path between the two poles along the surface of the insulator. This can either be between the socket parts, or between the wired parts. The leakage current causes further heating and micro-arcs where the leakage path opens due to current density. The micro-arcs further damage the insulator until there is nearly continuous micro-arcing. I suggest this is the source of the noise. The heat from the micro- arcing and the resistance of the carbonized surface of the insulator eventually lead to ignition and flames. I admit that this is a hypothesis. I believe that the process is more-or-less correct, but the details may not be correct. 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 Heald davehe...@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: No longer online until our new server is brought online and the old messages are imported into the new server. ------------------------------------------- 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 Heald davehe...@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: No longer online until our new server is brought online and the old messages are imported into the new server.
