>from old memories (maybe the memories are new and I'm old - can't tell the difference these days) I think it's a design flaw, although it passes safety - it fails safely. Vcc to ground makes -48 VDC which is telcom. PoE is Ethernet - NOT telcom. Ethernet has isolation in the standard - 1000 volts or more. witness the isolation transformer. Quantum leap of logic - if it's uses Ethernet in it's name, it follows the same premise of isolation. Thus PoE at each end, source and load, should be isolated to the same level, (how is an exercise for the power engineer) assuming there's a nefarious earth ground lurking about to provide a path for nasty test - which is referenced to earth or safety ground, or whatever it's called these days. LOTS of PoE gear is NOT isolated as I think it should be, I've smoked most of it (and damn they're hard to keep lit). But we did find some, no name brand, but it wasn't the EUT so I didn't care. Installation manual lists specifics. The EUT does have an optional intentional earth ground and that was beefed up to handle the surge everytime.
- Bill Indecision may or may not be the problem. --- On Mon, 11/10/08, Mark Gandler <[email protected]> wrote: From: Mark Gandler <[email protected]> Subject: Connecting DC output to earth ground To: [email protected] Date: Monday, November 10, 2008, 8:49 PM Hi, here is the case: Switch powered by 100-230VAC/48DC-1A adapter with earthed plug. At 48V side, "Vcc-" is connected through resistor directly to Earth ground. This switch has PoE port, which is used to power external device (PD, powered device), when there is a laptop connected through RS232 port to this PD. Laptop has his own power adapter, I assume grounded as well. In certain scenario, powered device in the middle, will get smoked. One claims it is due to the ground loop, based on Vcc- of power adapter being directly tied to chassis ground. Problem goes away after the connection is cut. Few questions: 1. are where any 60950 issues which could prevent tying DC(-) output to earth ground? (adapter has UL, TUV/CB certificates) 2. assuming the answer to #1 is "no", would this scenario require switch adapter and laptop adapter to be connected to different grounds? in order to create different potentials? and thus will make powered device in the middle the weakest point in the system? Thanks in advance for your suggestions. Mark ________________________________ Color coding for safety: Windows Live Hotmail alerts you to suspicious email. Sign up today. <http://windowslive.com/ xplore/Hotmail?ocid=TXT_TAGLM_WL_hotmail_acq_safety_112008> - ---------------------------------------------------------------- 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 - 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
