The external DC power supply needs to be SELV too, not just energy limited. _______________________________________________________________________________
Ralph McDiarmid | Schneider Electric | Solar Business | CANADA | Regulatory Compliance Engineering From: Ron Pickard <rpick...@equinoxpayments.com> To: EMC-PSTC@LISTSERV.IEEE.ORG, Date: 11/26/2012 12:38 PM Subject: Re: [PSES] POE creepage & clearances Hi Joe, I agree that an Ethernet circuit would be considered to be an SELV circuit and that would be true if the POE circuit were completely on premise generally, which would categorize this as a Class III product according to IEC/UL 60950-1 2nd Ed. given that the external power supply is a limited power source (LPS). However, TNV-1 creepage/clearance requirements would apply if the POE were to be exposed to overvoltages from telecommunication networks (essentially off premise) requiring Basic insulation. I make this distinction as Ian did not mention where the POE circuit originates. Best regards, Ron From: Joe Randolph [mailto:j...@randolph-telecom.com] Sent: Monday, November 26, 2012 12:43 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] POE creepage & clearances Hi Ian: I think the short answer to your question is that under 60950 there are no requirements for creepage and clearance distance between the Ethernet circuit and ordinary SELV circuits that are user-contactable. This is because under 60950, Ethernet is classified as an SELV circuit. There are no requirements to separate one SELV circuit from another. Where this issue becomes confusing is that under the Ethernet 802.3 standard, an Ethernet port must provide a 1500 VRMS isolation barrier between the Ethernet conductors and earth. This is a legacy requirement whose origins seem to have been lost in the sands of time. However, I believe the consensus view is that the original intent of this requirement was to protect against ground loops and was not related to user safety. Nevertheless, the 802.3 isolation requirement has sometimes been treated as though it is a safety requirement. Note that the 802.3 requirement is for a simple dielectric test, with no reference to creepage, clearance, or distance through solid insulation. So, in principle, there are no safety isolation requirements for your application, since both of the proposed power supplies have a SELV output. This makes the entire device a SELV circuit (unless there are other ports on the device that are not SELV). Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 (USA) j...@randolph-telecom.com http://www.randolph-telecom.com Dear colleagues We are developing a hand held product that is powered from +48V DC over Ethernet or from an external +12V DC wall wart PSU. The maximum internal voltage will be the +48V POE. Can anyone let me know what the creepage and clearance requirements between the ?primary? Ethernet circuit and the ?secondary? circuit. The product will be tested to IEC 60950 or possibly IEC 60065 so I am assuming a safety isolation creepage & clearance is required. Many thanks in advance; Ian McBurney Design Engineer Allen & Heath Ltd Kernick Industrial Estate Penryn, Cornwall TR10 9LU United Kingdom +44 (0)1326 370121 ian.mcbur...@dmh-global.com www.allen-heath.com A DMH Pro Company. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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