In message <[email protected]>, dated Fri, 17 Mar 2006, "Barker, Neil" <[email protected]> writes
>It is not clear whether your external power supply is Class 1 (basic >insulation + protective earth) or Class 2 (double insulated). If the >former, then the connection between the power supply and your >instrument should be providing the safety grounding. If the latter, >then providing the instrument does not generate any hazardous voltages >there is no need for a protective earth as all parts including the case >will be SELV. The complication arises when you connect to the PC, as it >is almost certainly a Class 1 apparatus, but since the PC interface >would be considered safe, the 'inadvertent' connection of the >instrument to Ground via the data cable is of no concequence as it is >either already connected (in the Class 1 case) or is double insulated >(in the Class 2 case). There is one other consideration. What does this instrument measure? Is it connected to something that could supply it with a large fault current? -- 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
