The toaster is a new production sample for approval. The interior is clean without the sign of use.
Scott > On 2 Oct, 2015, at 4:42 am, Ed Price <[email protected] > <mailto:[email protected]>> wrote: > > As the appliance is a toaster, could the switch area have been contaminated > by carbonized bread particles and/or burnt residue (raisins, glaze > drippings)? This might account for the length of arcing, although you would > think that good design would include a shield to keep such residue away from > the contacts. > > Rich, would you talk a little about reforming of the switch contacts by the > molten metal? If I were to imagine that I was looking at the center of a > contact (along the axis of the arc), the current should set up a circular > magnetic pattern. So, are you saying that the molten metal is “swept” around > in a circle until it cools to the solid state? And just for fun, how many > microseconds might it take for the molten metal to solidify? > > Ed Price > WB6WSN > Chula Vista, CA USA > > -----Original Message----- > From: Richard Nute [mailto:[email protected] <mailto:[email protected]>] > Sent: Thursday, October 01, 2015 11:12 AM > To: [email protected] <mailto:[email protected]> > Subject: Re: [PSES] Arc flash to earthed parts > > Hi Scott: > > > When a switch opens (at something other than the zero-crossing), an arc is > created and molten metal of the contacts is likely. (In fact, some contact > designs use the molten metal to re-form the > contacts.) > > The molten metal is accelerated (at right angles to the current direction) by > the magnetic field. > > What is unusual is the length of the arc -- 1 inch. And, that the arc was > from the switch contacts to the earthed parts. The current through the arc > to the earthing conductor can be sufficient to trip the RCD. > > One hypothesis is that the current in the contacts created an excessive > amount of molten metal which allowed the arc to also go through the molten > metal droplets to the earthed metal. This would explain both the metal on > the earthed part and the arc. Excessive contact heating could be caused by > contact resistance being high (but not too high). > > > Based on your description, I would hypothesize that the switch contact > resistance was high; the switch is worn out, or has inadequate ratings. > > I don't know of any standard that would address this issue. The situation is > analyzed by science and engineering, and appropriate changes to the > construction to prevent recurrence. > > > Good luck and best regards, > Rich > > > > > > > -----Original Message----- > > From: Scott Xe [mailto:[email protected] <mailto:[email protected]>] > > Sent: Wednesday, September 30, 2015 11:22 PM > > To: [email protected] <mailto:[email protected]> > > Subject: [PSES] Arc flash to earthed parts > > > > Dear Members, > > > > I recently encountered a symptom on a toaster. > When > > turning off by pressing the quit button, there > was an arc > > flash from the mains switch contacts to earthed > parts > > where the separation greater than 1 inch apart > in air > > occasionally. The mains contacts have a sign of carbonisation on the > > open/close contact points > and > > melted in a small area of the contact leaf. The > switch > > and the earthed parts are inside the plastic > case without > > the access by the users. It may trip the RCD > during arc > > flash. In addition, there was vaporised copper > layer on > > the earthed part. It did not have immediate > danger to > > the user and definitely not a good product. How should we categorise > > this type of fault and is > there any > > reference standard for it? > > > > Thanks and regards, > > > > Scott > > > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. To post a message to the list, send your e-mail to > <[email protected] <mailto:[email protected]>> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > <http://www.ieee-pses.org/emc-pstc.html> > > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ > <http://product-compliance.oc.ieee.org/> can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.org/ <http://www.ieee-pses.org/> > Instructions: http://www.ieee-pses.org/list.html > <http://www.ieee-pses.org/list.html> (including how to unsubscribe) List > rules: http://www.ieee-pses.org/listrules.html > <http://www.ieee-pses.org/listrules.html> > > For help, send mail to the list administrators: > Scott Douglas <[email protected] <mailto:[email protected]>> > Mike Cantwell <[email protected] <mailto:[email protected]>> > > For policy questions, send mail to: > Jim Bacher: <[email protected] <mailto:[email protected]>> > David Heald: <[email protected] <mailto:[email protected]>> > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. To post a message to the list, send your e-mail to > <[email protected] <mailto:[email protected]>> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > <http://www.ieee-pses.org/emc-pstc.html> > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ > <http://product-compliance.oc.ieee.org/>can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.org/ <http://www.ieee-pses.org/> > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe) <http://www.ieee-pses.org/list.html> > List rules: http://www.ieee-pses.org/listrules.html > <http://www.ieee-pses.org/listrules.html> > For help, send mail to the list administrators: > Scott Douglas <[email protected] <mailto:[email protected]>> > Mike Cantwell <[email protected] <mailto:[email protected]>> > > For policy questions, send mail to: > Jim Bacher <[email protected] <mailto:[email protected]>> > David Heald <[email protected] <mailto:[email protected]>> > - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) 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]>
