Scott, Defective cords have been around long before someone got the idea to manufacture them offshore. How would you be able to tell, without using the "Hershey" criteria, if a power cord is any good?
Dan Kwok Scott Lacey wrote: > > 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: [email protected] > [mailto:[email protected]]On Behalf Of Jim Eichner > Sent: Thursday, October 25, 2001 3:40 PM > Cc: [email protected] > 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:[email protected]] > Sent: Thursday, October 25, 2001 12:14 PM > To: [email protected] > Cc: [email protected] > 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: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: [email protected] > Dave Heald [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > 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: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: [email protected] > Dave Heald [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] 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.
