On powered Ethernet interfaces, 48 VDC is delivered from Ethernet switches to IP phones with + over one twisted pair and - over another pair of a CAT5 cable. The power is not permanently connected to the connector or cable. It is switched to the socket/plug only if an IP phone is detected on the other end of the cable. If someone disconnects the phone, the power will be disconnected from the socket by a switch (or relay).
In the integrated types of connectors/socket, with transformer and some other components built-in, the distance between + and - of 48V can be as little as 0.02" on a surface of a little PCB. 48 V over 0.02" gives E field strength of 94 kV/m. Is there any safety or reliability concern with 48V possibly permanently across 0.02" spaced pads on a PCB surface? I believe safety-wise it is okay, but I am not sure if electromigration or something else may cause long-term problems, since the phones are more-less permanently connected. Any comments? I am not particularly interested in the power-supply design aspect, but more in this specific situation with 48V across small creepage distance. Thank you, Neven ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
