In message <[email protected]>, dated Tue, 18 Apr 2006, Stuart Miller - Ablewisp <[email protected]> writes
>After connecting the data cable (Firewire, already connected to the pc) >to the drive, I touched its metal case while touching the outer of the >dc connector and got an unpleasant tingle. You are unusually sensitive, then, or a particularly sensitive part of your skin, such as the lateral surface of a small finger, was involved. >I measured 230 V from the metal case to the outer of the dc connector >(not connected to the portable hard disk). Yes, that is not unusual. In some products, the floating voltage is 115 V, because there are two equal X-capacitors from the mains poles to the case. But for EMC reasons, the capacitances these days are often not equal. >To isolate the drive from ac ground, I removed the data cable from the >drive and measured 230V from the metal case to ac power ground (the >drive is insulated from the pc case by plastic feet). Current was >around 0.2mA. The standard EN 60950-1:2001 (Table 5A) allows 0.25 mA, measured with the test circuit shown in Annex D. Your measurement may show a higher current that the test circuit does. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk 2006 is YMMVI- Your mileage may vary immensely. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
