Ubiquiti AP-AC-LR - ok with a POE switch

Question about POE devices compatibility wrt Voltage.

I have a Ubiquiti AP-AC-LR at home, about five years old now. This is powered by a dedicated power injector which was supplied with the unit. The injector is rated at 24VDC.

Looking at specs of at POE switches they are often rated at 48VDC.

So would the AP-AC-LR work with a 48v injector - or just get wrecked?

Or is there a caution, not all POE devices can play nicely?

802.3af, 802.3at, and 802.3bt are all known as “Active” POE. This means that before power is enabled on a port, the PSE (Power Sourcing Equipment) will perform an active check for whether a PD (Powered Device) is connected on the line. Some specific circuitry has to exist on the PD for it to be detected. The goal is for a shorted line or non-compliant device to not be detected.

By contrast, things like the POE injector you have are “Passive” POE. They just output power without checking.

Yes, if you somehow had a Passive 48V source, and connected a device that wasn’t properly designed, it will probably kill the device. But an Active 48V source should instead just not detect the AP and not output power.

The UAP-AC-LR has had a few revisions over the years. If yours is old, then it probably is 24V Passive only. But newer ones support 48V Active POE as well. On the back of the AP is a “Date code”, which is the 2-digit year and 2-digit week. 1808 would be the 8th week of 2018. Anything with a date code later than 1642 is supposed to support active POE. Also, the label on the back should have additional text on it to indicate it is 802.3af compatible if it is one of the newer ones - the older ones will just show the 24V.


Thanks. I will add your response to my personal wiki!