I read in !emc-pstc that John Woodgate <[email protected]> wrote (in <[email protected]>) about 'Circuit Breaker Tripping Dring Fault Tests' on Wed, 29 Jan 2003: >I read in !emc-pstc that Peter L. Tarver <[email protected]> >wrote (in <[email protected]>) >about 'Circuit Breaker Tripping Dring Fault Tests' on Wed, 29 Jan 2003: >>In a typical household operating at 120V, it's unlikely >>that a fault current available to Pluggable Equipment Type A >>will be much above 5kA, even if the outlet supplying the >>equipment is within 5 ft. of the service entrance. In a >>typical household operating at 240V, the available fault >>current will be somewhat higher (approximately doubled +). > >H'mm. IEC 60725 gives a 'reference impedance' (a sort of weighted >average, omitting extreme values) for a 230 V 50 Hz 100 A service-rating >household supply as 0.47 ohms at the service entry. Allowing another >0.5 ohms for the mains wiring and the flexible mains lead, we get 230 V >and 0.97 ohms at the appliance, giving a prospective short-circuit >current of about 240 A. The appliance fuse should be able to interrupt >that without exploding. > >UK plug-top fuses are tested to break 6000 A safely, though.
There is a proposed amendment to IEC/EN 60950-1 requiring a test of the protective conductor network at *prospective short-circuit current* for the time it takes for the mains circuit protective device to operate. The details are controversial at present, because the test currents appear not to have taken into account the differences between prospective short-circuit currents in different wiring systems and supply voltages. Given that reservation, the lowest test current is 200 A. The amendment is aimed at protective conductors which are surface or internal traces of multi-layer printed boards. It is said that such traces have failed in the field under high-current fault conditions. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! 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: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
