Richard, You bring up a point which I have debated many times in the past. Since the wire can handle more current in a fault condition than it is rated, the only real way of knowing is to do an overload test as you suggested? Slowly increase the output load while measuring the wire temperature until the PSU shuts down or the wire overheats. Since this would simulate a fault condition, do we use 150ºC (calculated for a 40ºC ambient) as our upper limit for the wire temp? Is this how it is done?
When we have done this test in the past we generally find out the wire can handle much more current than we thought, but connectors tend to overheat first, so don't forget to check the connectors. It is too bad that the world isn't designed so you can take a 10A output, run it through a 10A wire, a 10A connector, and a 10 amp load and not have to worry about what happens in a fault condition. The Other Brian -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Richard Nute Sent: Monday, August 01, 2011 6:06 PM To: 'Ken Javor'; [email protected] Subject: RE: Electrical design challenge > The short circuit current wouldn't be much greater > than rated current for any length of time, because > the source is the power supply, not the ac mains. Typical brick-type power supplies will put out about twice rated current into a short-circuit. So, 10 A rated becomes 20 A short-circuit. Wire size is usually based on rated current. Supposedly, short-circuit current can only exist for a short period of time due to the overcurrent protection -- the short time for operation of the overcurrent device being less than that necessary to overheat the wire insulation. However, brick-type power supplies typically don't have overcurrent protection on the output. Without overcurrent protection, the safety professional must judge whether to size the wire for rated conditions or short-circuit conditions. Richard Nute Product Safety Consultant Vancouver, Washington, USA - ---------------------------------------------------------------- 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://product-compliance.oc.ieee.org/ Graphics (in well-used formats), large files, etc. can be posted to that URL. 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]> ________________________________ LECO Corporation Notice: This communication may contain confidential information intended for the named recipient(s) only. If you received this by mistake, please destroy it and notify us of the error. 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://product-compliance.oc.ieee.org/ Graphics (in well-used formats), large files, etc. can be posted to that URL. 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]>
