Power-over-ethernet to non-PoE device

Question

While I can find lots of information about PoE, I'm finding little about "gotchas" or "warnings".

That being said, what would happen if I configured a switch to give PoE then plugged that into a device that doesn't support PoE? Would it damage the endpoint device?

Solution

No, you won't damage those devices. There are occasional posts to the contrary online but for the most part it seems that PoE is only activated after an initialization request is sent. A better discussion can be found here: http://community.spiceworks.com/topic/187505-mixing-poe-and-non-poe-devices

PoE Detection occurs like this "In order to avoid damage to non-PoE devices, a key component of the 802.3af PoE standard is detection. PSEs must be able to detect the presence of a PoE-enabled device before sending power, and must be able to detect when the powered device is no longer present and remove power. To achieve accurate detection, a low-level detection current is sent from the PSE through the cable and the response is analyzed to determine if a compliant device is attached."

The rest of the explanation of PoE and the standard can be found here: http://www.network-1.com/poe/poe_ovw.htm

Comments

[Callen L]

I can say from experience, all of our corporate data center switches are configured for PoE for our phones, but we can safely plug those network cables into any other device as well. Laptops, Desktops, dumb switches etc. Hopefully someone can explain the science of it in the answers.

[jspinella]

Ubiquiti for a while had something called "passive PoE" which does not conform to 802.3af and sends 48v over the ethernet cable at all times. This will kill or at least let some of the magic smoke out of non-PoE devices. They discontinued this terrible idea, but plenty of Ubiquiti passive PoE products are still in use today (e.g. the EdgeRouter line).