Dave, 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). Best regards
Neil R. Barker CEng MIEE FSEE MIEEE Manager Compliance Engineering e2v technologies (uk) ltd 106 Waterhouse Lane Chelmsford Essex CM1 2QU UK Tel: (+44) 1245 453616 Fax: (+44) 1245 453410 Mob: (+44) 7801 723735 From: [email protected] [mailto:[email protected]] Sent: 17 March 2006 16:05 To: [email protected] Subject: lab equipment connected to PC Gents, Situation: I am building an instrument that interfaces to a DAQ card in a PC. The instrument is powered by an external AC-DC power supply supplying +/- 12 volts at 100 mA. The instrument metal case is connected to the PC Common via the DAQ card cable. Question: Is this safety grounding arrangement legal under EN61010? Do we need to provide more solid earthing of the instrument case? Dave Cuthbert Micron Technology, Inc. - ---------------------------------------------------------------- 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 - ---------------------------------------------------------------- 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
