I do not think that Telecordia and IEEE standards are addressing just the isolation requirements for devices connected to wired ethernet or wifi. There are problems with mains isolation and OV and misc external wiring.
Recently looked at a problem for a local school - they thought that they had isolated some battery-operated equipment using wifi through a wireless router, but it was connected to several other devices through a wired RJ connector on the back of the router, that were in turn connected to the 'isolated' wireless device. One of the devices was outside the building and they had people getting "mild" shocks. As I do not have much experience in this area (paging Mr Joe Randolph, please), I would appreciate advice on how/if the requirements of UL60950-1 clause 6.1.1 is intended to affect the construction requirements of this stuff. thanks, Brian From: [email protected] [mailto:[email protected]]On Behalf Of Joe Randolph Sent: Friday, September 11, 2009 12:30 PM To: Goedderz, Jim; [email protected] Subject: Re: Additional electrical requirements - isolation On 9/11/2009, Jim Goedderz wrote: Are the Additional Electrical Specifications, Isolation, para 33.4 of IEEE802.3af (1500Vdc hipot) satisfied by the input power connection and the router. It wouldn't seem necessary that the cameras themselves need to provide 1500Vdc isolation from their Ethernet connection to SELV. Bottom line, would the system as described be considered compliant with IEEE802.3af? Would the camera be considered compliant with IEEE802.3af? Hi Jim: I think the answers to your questions depend on some additional details about the system design and the customer involved. Following are some points to consider: 1) IEEE 802.3af is not a regulatory requirement. It is an industry standard and compliance with any or all of its requirements is optional. 2) For safety compliance per EN 60950, a conventional Ethernet connection, even a POE version, is classified a SELV circuit. So, it is important to keep in mind that the 1500V requirement you are describing is not a regulatory requirement for UL 60950 safety compliance. It is a legacy requirement that has been embedded in the Ethernet specifications since the early days of Ethernet, at a time when the industry thinking about safety analysis was less precise than it is now. I believe that the main reason for the 1500V requirement was to prevent ground loops in a system where each node might have a different local ground potential. I'm not sure how they arrived at 1500 volts. If you want the POE port on the camera to be "IEEE 802.af compliant," you will have to implement the specified 1500V barrier. However, you might be able to meet the requirement by careful physical design that prevents user contact with the internal circuitry. Similarly, if you want each of the POE ports on the router to be "IEEE 802.af compliant," you will need to implement the specified 1500V barrier on each of those ports as well. The situation changes if your cabling arrangement, camera, and router are not specified to be "IEEE 802.af compliant" and compatibility with generic Ethernet ports is not required. In other words, the cabling and signaling use a proprietary scheme that is not intended to be compatible with industry-standard Ethernet interfaces. In that case no isolation barrier would be required in the camera or the POE-like ports on the router that connect to the camera. However, if the router has an Ethernet port that is intended to connect to the internet via the home's conventional Ethernet LAN, that one port should have the 1500V barrier if you want to call it "IEEE 802.af compliant." I'm sorry if this seems confusing at first, but I think it can be sorted out by using a step-by-step approach to define more clearly what requirements you are trying to meet and why. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 (USA) [email protected] http://www.randolph-telecom.com - 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]>
