My standard answer to POE questions....Mostly stolen from or repeated in a Network Computing issue about 2 months ago.
PoE factoids: PoE uses the spare pairs *or* the data pairs (which one to use is automatically detected) in an ethernet (10 or 10/100) cable to carry -48V dc from the power sourcing equipment (PSE) in an endpoint switch (or midspan hub) to the powered device (PD) appliance at the other end of the cable. Clearly, use of the spare pairs requires that they be connected all the way from PSE to PD, which may not be the case in some legacy installations. The PoE power limit is 13W per PSE port. A new standard is being discussed which will raise this to about 25W. But don't expect it for a few years and it's primary use is security cameras requiring pan/tilt/zoom. Newer ethernet switches include the PSE function internally, but Midspan Hubs can also be used to insert PoE power in legacy installations. Legacy PDs can also be powered by PoE 'splitters' or 'taps', which pull the power from the ethernet and deliver it to the PD via a short cable. PoE appliances include: Phones Cameras RF ID readers Displays Wireless Access Points Musical instruments The PoE standard is IEEE 802.3af. It was approved about a year ago. There are previous, proprietary PoE schemes from a number of vendors. PoE's -48 V dc is designated as Safety Extra-Low Voltage (SELV). SELV (safety extra low voltage) is a secondary circuit which is designed and protected so that under normal and single-fault conditions, the voltage between any two accessible parts does not exceed a safe value (42.2 V peak or 60 V DC). It is lower than standard telephone network voltage (TNV). > -----Original Message----- > From: Kevin P. Fleming [mailto:[EMAIL PROTECTED] > Sent: Monday, November 08, 2004 2:14 PM > To: Asterisk Users Mailing List - Non-Commercial Discussion > Subject: Re: [Asterisk-Users] [OT] Old Building Needs a New > Telephone System > > Tim Donahue wrote: > > First, I will admit that I have not worked with PoE before so I'm > > asking this for my own benefit as well as the OP's benefit. > Doesn't > > PoE require at lest 3 pairs to be availible? I know that > pins 1, 2, > > 3, and > > 6 get used for ethernet communications and doesn't the power get > > transmitted over pins 4 and 5? > > A PoE-enabled connection needs all four pairs. Two pairs for > Tx/Rx, one pair for power, one pair for ground. > _______________________________________________ > Asterisk-Users mailing list > [EMAIL PROTECTED] > http://lists.digium.com/mailman/listinfo/asterisk-users > To UNSUBSCRIBE or update options visit: > http://lists.digium.com/mailman/listinfo/asterisk-users > _______________________________________________ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users