On 8/7/2006, Derek Walton wrote:
I've been asked a question about UL864 for smoke control systems. This requires surges of around 2400V to be applied to all IO lines including the Ethernet port. Are there any design specification limitations I soul be worried about implementing suppression for this pulse. I specifically mean, can I use MOV's Transorbs to chassis etc? I was under the impression that Ethernet could be transformer isolated, and then I'd let the transformer take care of the surge... Hi Derek: Ethernet interfaces are always transformer coupled. The line signals are very sensitive to capacitive loading, so you have to be careful about the transient suppression you choose. Another factor is that within the Ethernet specification itself there is a requirement for 1500 VRMS isolation, so line side protection to ground can be problematic. Interestingly, this isolation requirement does not derive from any current safety regulatory requirements. I think it is an artifact from considerations that were in place at the time that Ethernet was standardized. The telecom spec Telcordia GR-1089 applies surges of 800 V differential and 1500 V common mode to Ethernet interfaces, and I have some experience designing for these. In most cases the transformer itself can be used for the bulk of the protection scheme, with possibly a differential protector across each pair on the line side. On the chip side of the transformer you can use some carefully selected steering diodes and series limiting resistors, although series limiting resistors cannot be used in the transmit pair of some Ethernet chips. The devices placed on the chip side of the transformer only have to handle the residual energy that couples through the transformer. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 (USA) [email protected] http://www.randolph-telecom.com <http://www.randolph-telecom.com/> ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________ - ---------------------------------------------------------------- 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
