I agree with your analysis. Heating of any junction can occur at high current when the contact impedance is not great due to poor contact pressure or other factors like corrosion. We all have seen this exact same type of failure in connectors, relays, terminal blocks, fast-on connectors, etc.. The trick is to make sure the rest of the design can allow such as fault without causing a hazard.
The Other Brian -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Richard Nute Sent: Tuesday, October 09, 2012 7:45 PM To: Schaefer, David; [email protected] Subject: Re: [PSES] What's the deal with Wire Nuts? >From the photo, I believe we see two wire nuts, the plastic cases of which >have fused together. One wire nut connects the two black (live) wires, and one wire nut connects the two white (neutral) wires. (Note the smoke deposits on the white wires.) A yellow wire nut is rated for minimum 2 #18 up to 4 #14. So, I suspect that each wire nut connects 2 #14 wires, where #14 is the most common 120-V, 15-A wire. I doubt the overheating resulted in a L-N short because such a short would have resulted in arcing (no evidence) and burning of the plastic, and considerably more overheating. Of course, if such a short did occur, then the overcurrent device operated quickly and prevented further heating. My hypothesis is that the two wire nuts were in contact with each other. And the load was quite high, resulting in heating of the contact resistance in both wire nuts. The plastic melted, the two nuts fused together, and the wires touched. Since the load was already quite high, the overcurrent device was near its operating current, and the overcurrent device operated quickly before any further damage was done. Other hypotheses? I wouldn't blackball wire nuts. My house has lots of wire nuts in its electrical installation; no failures after 25 years! Best regards, Rich -----Original Message----- From: Schaefer, David Sent: Tuesday, October 09, 2012 6:11 AM To: [email protected] Subject: Re: [PSES] What's the deal with Wire Nuts? After pulling this out of a piece of equipment, I have serious doubts about the long term use of wire nuts. http://s139.photobucket.com/albums/q296/user8888/?action=view¤t=2012-10-08185745.jpg David Schaefer Senior EMC Engineer TÜV SÜD America Inc Office: 651 638 0251 Cell: 612 578 6038 Fax: 651 638 0285 -----Original Message----- From: Doug Powell [mailto:[email protected]] Sent: Monday, October 08, 2012 10:45 AM To: [email protected] Subject: [PSES] What's the deal with Wire Nuts? At the risk of redundancy, I would like to re-open a question from 2008 "What's the deal with Wire Nuts?" http://www.mail-archive.com/[email protected]/msg56599.html The original discussion seems to track well with my own opinion on the use of these wiring devices, but this is based my opinion. I am aware of many American appliance manufacturers who use these devices and still obtain their safety certifications. It is my *opinion* that any equipment destined for the European market should not use these devices but I cannot find any direct prohibition on their use. The IPC 620 standard may have limits but this is more like a workmanship standard. Several reasons might be used to prohibit their use: 1) Temperature ratings 2) Secondary securement of conductors 3) Insufficient coverage of bare metal parts and resulting electrical tape used (creepage problem) 4) No limit to the number of conductors 5) Over/Under twisting of the connector 6) Metallic insert or non-metallic This time around my context is equipment that falls under the scope of IEC 61010-1 and its derivatives. Has anyone seen a definitive answer to this question? -- Thanks, -doug Douglas E Powell [email protected] http://www.linkedin.com/in/dougp01 - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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Thank you. - ---------------------------------------------------------------- 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://listserv.ieee.org/request/user-guide.html 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]>
