I read in !emc-pstc that Peter L. Tarver <peter.tar...@sanmina-sci.com> wrote (in <nebbkemlgllmjofmoplekehbedaa.peter.tar...@sanmina-sci.com>) about 'Circuit Breaker Tripping Dring Fault Tests' on Thu, 30 Jan 2003: > >John - > >That impedance value is suprisingly high,
It applies to 230 V 50 Hz systems only. SC77A/WG2 has been given a too limited amount of data on 120 V 60 Hz systems to deduce a reference value, but it seems to be rather less than half the 230 V value, because permitted voltage tolerances in 120 V systems tend to be +/-5%, less than in Europe (6 to 10%). >but tends to >support the contention that the fault current at an outlet >will be much lower than was suggested (65kA, which, to me, >appeared more like a peak surge current than a fault >current). Yes, 65 kA is way too high. > >For those interested, below are what the IEC Web Store has >to say about IEC 60725. > >Title: Considerations on reference impedances for use in >determining the disturbance characteristics of household >appliances and similar electrical equipment > >Abstract: Records the information that was available and the >factors that were taken into account in arriving at the >reference impedance of 0.4+ j 0.25 ohm which has been >incorporated in IEC 60555. Has the status of a technical >report. A revision is under way. Postpone your buying decision.(;-) It doesn't alter the reference impedance but adds information of calculating the impedances of (particularly) higher-current services, applicable to any system voltage and permitted voltage variation. > >0.5 Ohm seems large for a flexible cord. > 0.5 ohms is 0.2 ohm total for the two conductors of the flexible plus 0.3 ohm total for the two conductors of the feed to the wall socket. All in a 230 V system. It's just an example. -- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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
