Your EFT tester is ground bonded to the Horizontal Reference Plane which is the return path for the burst generator. The test according to 61000-4-4 couples common mode transients to the conductors you are testing. Most labs only test all conductors at the same time which is a true common mode setup, but the testers allow you to couple to any combination of conductors (if you are testing the AC mains).
For instance, if you are testing only Line and Neutral, the EFT is common mode coupled onto these conductors. Nether is the return path and the untested PE conductor does not intentionally become the return path. For your information, it is my understanding that the USB interface is only specified up operate to 1KV EFT so it does not surprise me that it should fail at 1.3KV. Our company played around with using USB communication between a standard PC and device we make but wanted to use it in an industrial environment. The only way we could get it to past EFT at 2KV was to add a ground bonding wire braid between the PC chassis and EUT. In the end we decided to use Ethernet instead of USB. Good luck, The Other Brian From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Tuesday, December 02, 2008 12:14 PM To: [email protected] Subject: EFT / B pulses applied on the protective earth conductor Dear Experts, For the EFT / B testing for the noise is injected on the protective earth conductor which will be the return path. In our USB device, signal ground (- ve of 5 volts DC supply from the USB) and USB cable shield are same points. USB cable shield is connected to chassis of the PC which is the protective earth point of the 3 pin 230 volts 50 Hz single phase AC input. Isolating the shield from the 5 volts -ve is worsening the results and with direct connection between shield and 5 volts -ve the device fails at 1.3 KV. My understanding is, for the noise injected on the Line & Neutral protective earth conductor is the return path. Is this correct? I request your guidance here. Sincerely SCM Microsystems (India) Pvt. Ltd. K. Balasubramanian Modules 0506, 0507 & 0508, D - Block, Manager - Hardware South Wing, TIDEL Park, Tel : +91 44 42931391 #4, Rajiv Gandhi Road,(formerly Canal Bank Road) Fax :+91 44 22540029 Taramani, Chennai - 600113. India E-mail:[email protected] Web : http://scmmicro.com 'This email and any attachment may contain confidential information and are intended solely for the use of the named recipient(s). If you have received this information in error, you are prohibited from reading, copying, distributing and using the information. If you are not a named addressee or otherwise an intended recipient you are requested to immediately notify the sender and to delete this email and all attachments from your system.' - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]> LECO Corporation Notice: This communication may contain confidential information intended for the named recipient(s) only. If you received this by mistake, please destroy it and notify us of the error. Thank you. - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
