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This might be a silly question but we rolled out a large batch of VoIP Phones. Some due to port shortages have been bridged and PoE turned on. Management right now on the switch is tedious and we are debating turning PoE on for all ports so we can ease the burden of bridging new phones as they come in.

The question is does keeping PoE turned on for a port that links to a device (i.e. a desktop) that doesn't need it bad in any way for the device? Is there any chance of power disruptions or other ill-effects?

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2 Answers 2

up vote 8 down vote accepted

If the PoE switch is 802.3af compliant (most are, but there are other implementations out there. I believe Cisco has their own) then it's safe to enable PoE on every port.

Basically, the PoE switch will check for a certain resistance between two of the pairs of wires on the other end of the device. If the resistance is within a certain tolerance, the device provides PoE power to the port. If the resistance is out of tolerance, then it does not.

Unless you have a very weird fault on the other end of the line, then the switch will not trigger its PoE functionality for that port.

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PoE is negotiated between the devices on each end of the link, so there is no danger of the switch supplying power to a device that doesn't request it.

http://en.wikipedia.org/wiki/Power_over_Ethernet#Powering_devices

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