In message <64D32EE8B9CBDD44963ACB076A5F6ABB01C4C6E4@Mailbox-Tech.lecotech.local>, dated Tue, 2 Aug 2011, "Kunde, Brian" <[email protected]> writes:
>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? Some wire ratings are based on a 70 C ambient. It is important to take into account how the wire can lose heat to its surroundings. Consider a wire clipped to a steel beam in an unheated warehouse, and the same wire embedded in thermal insulation in the roof-space of a heated building. > >When we have done this test in the past we generally find out the wire >can handle much more current than we thought, Yes, another aspect is that the 70 C rating may also be based on a service life of 20 years. A simple test obviously doesn't look at slow thermal degradation. > but connectors tend to overheat first, so don't forget to check the >connectors. This is very important. The wire may test OK for temperature rise in free air at 25 C at 10 times its rated current, but the connector probably won't. > >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. If it was too easy, it wouldn't be so fascinating. (;-) -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK When I point to a star, please look at the star, not my finger. The star will be more interesting. - ---------------------------------------------------------------- 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]>
