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Is it possible to power the RUT955 from Ubiquiti's Gigabit 24V passive PoE injector? Since the Gigabit injector uses three wire-pairs for power and not just two, I am actually more concerned about the Gigabit injector's pin-out, and whether this is compatible with the RUT955's pin-out for PoE.

The Gigabit injector provides power on the following wire-pairs:

1. V+ on pair 4-5.

2. V- on both pairs 3-6 and 7-8.

According to the RUT955 wiki, it only uses pin 5 for V+ and only pins 7-8 for V-. I would like to use an Ethernet cable with all four wire-pairs (wired according to T568A), so that I can also use it for other things later. In that case, would the two pin-outs be compatible, or would I have to make a cable that only uses certain wires / pins?

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Hello,

Yes, the RUT955 is able to power via PoE and according with the specification you wrote, It matches with the wiki information.

"Just take care to read about the 802.3af-2003 and IEEE 802.3at standards."

Take a look to this link.

https://wiki.teltonika-networks.com/view/RUT955_Powering_Options#Simultaneous_powering

Regards.

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Thanks for getting back to me. However my concern was that the "extra" pins 3 and 6 could somehow create a short. However some measuring showed that that would not be the case.
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After reading up a bit and making some measurements with a multimeter, I can give some feedback. From measuring the impedances between the pins of LAN1 of the RUT955, it looked like pins 4-5 (+) and 7-8 (-) were isolated from pins 1-2 and 3-6. Hence it seemed safe to apply a negative potential to pins 3-6 without closing the circuit with pins 4-5 (+) and frying some electronics. This was also the case - when I connected the Gigabit injector, the RUT955 powered up fine without any smoke or other problems.

However a word of caution - the impedances of the pins of LAN2 and LAN3 were a bit different. On those ports pins 4-5 are connected via 150 Ω to pins 1-2 and 3-6, which is normal for non-PoE ports. However that would mean that if you accidentally connected that kind of injector to LAN2 or LAN3 (perhaps also LAN4 / WAN), the connection between pins 4-5 (+) and pins 3-6 (-) will close the circuit, which will most likely damage the port and possibly the router. (Pins 7-8 seemed to be capacitively coupled to the other pins, offering some DC-isolation. I assume that this is to provide PoE-protection for the "normal" scenario of only using pins 4-5 (+) and 7-8 (-) for PoE.)

However use at your own risk, since your scenario might be a bit different.
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Hello,

Thanks, as you told just the LAN1 port is able to power via PoE.

There is already now an update in our wiki to warn about it.

Regards.