The return for the SELV output is not necessarily considered "safety grounding". I do not know how "PC Common" is referenced. Construction requirements for either current path is determined on if the devices are Class 1, and what the max fault current the conductors would be required to carry.
The requirement for protective earth is dependent on the rating and conditions of acceptability for the device's power supply. If there is a high enough potential between the computer chassis and the DAQ power source, then dangerous touch current levels may be available at either chassis. It should be noted that allowed ground leakage current levels for EN61010-1 can exceed those allowed in accordance with EN60950-1, but the intended end-user and operating conditions are supposed to mitigate. Use your judgment... luck, Brian From: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of drcuthb...@micron.com Sent: Friday, March 17, 2006 8:05 AM To: emc-p...@ieee.org 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 emc-p...@ieee.org 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 emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
