In message <0B2083BBF5664BCCA52EF295AE71B4B5@christopher>, dated Tue, 15 Sep 2009, Chris Wells <[email protected]> writes:
>I can see where the emission issues have a lot of meaning in telecom >links since we need to keep this common/public link clean. At the same >time I appreciate that my local proprietary RS485 link should strive to >meet the same goal but I do want to know when I will be regulated to do >so and want to see the boundaries clearly. We all need to know where >the line lays and try to keep on the proper side. I don't think you will 'see the boundaries clearly' by reading the standards, and in Britain you will only be 'regulated' if a case of interference actually occurs. The reason is that there are too many variables affecting the potential emissions from these cables. To be 100 % (actually only 99.9.. %) sure, one would have to test for conducted common-mode emissions every port that could have a cable longer than about 1 metre connected (0.1 wavelength at 30 MHz). This is clearly (I think) over-onerous, as 99.9.. % of products would pass. The EMC Directive is written so that manufacturers can (and have to) use their own judgement about what testing is necessary. So it's really up to you what you do. For example, you could pre-compliance test some of your daisy-chained RS-485 products, to see whether there is any need to test them fully. > >Another tangent on telecom is in regards to safety. To me telecom >brings in exposure to surge from links outside of a building. Telecom >POTS systems represent some of the more dangerous circuits that you can >be exposed to. Well, they would be, if the system operator didn't have a lot of protection fitted. POTS wring is dangerous if there is a nearby lightning strike, but then so is practically anything metallic that isn't deeply embedded in the planet. > In contrast an RS485 system restricted to the inside of a building >does not represent the same threat. This is certainly the case. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk Things can always get better. But that's not the only option. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - 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]>
