Question

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?

Answer 1

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.

Comments

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.

Answer 2

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.

Comments

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.

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Hi,

Looking for couple of days to power up my Teltonika rut955 housed by QuWireless QuMax antenna I found that Qu they also produce their own Passive POE dedicated to all QuSpot, QuMax and QuMini antenas with Teltonika routers installed inside which was my case.

QuPSU P248U Passive PoE Power Supply UK

Can be found here;

https://www.forestrock.co.uk/product/qupsu-p248u-passive-poe-power-supply-uk/