10 replies to this topic

[KennyL]

I did a stupid thing and accidentally connected Unifi Ubiquittis POE injector into VU+ Ultimo 4k's ethernet port. LAN actually worked while I did that, and I see no obvious signs of damage when using the receiver, but I am still wondering if it potentially did some damage on the receiver that will manifest itself after a while? Do VU+ receivers have some kind a protection on the ethernet port? PoE injector is of the dumb type, it always sends 24V over the cable.

Edited by KennyL, 22 June 2017 - 13:31.

[WanWizard]

PoE is send over the wire pairs not used for Ethernet, so changes are you'll be fine.

 

I haven't seen any damaged devices, and I used to have a network environment with over 55.000 PoE ports.

[KennyL]

From what I understand standard PoE doesn't send any power unless device requests it first, unlike the simple injectors like the one I have that are always on. As far as wires go, 100 Mbps uses all but two wires, while 1Gbps uses all? I had it connected through 100 Mbps switch, so that may be what saved me.

[Erik Slagter]

PoE is send over the wire pairs not used for Ethernet, so changes are you'll be fine.

That's untrue for Gb ethernet, as all wires are used then.

 

But as KennyL says, PoE needs to be explicitly requested before it's enabled. Or you must have a very dodgy one... Even then the ethernet signalling lines are protected by a transformer that will withstand up to 2.5 kV (short spike), so I guess they will also cope with 48 V.

[Rob van der Does]

But as KennyL says, PoE needs to be explicitly requested before it's enabled. Or you must have a very dodgy one... Even then the ethernet signalling lines are protected by a transformer that will withstand up to 2.5 kV (short spike), so I guess they will also cope with 48 V.

That's only true for active PoE.
There's also passive PoE: in that case the default PSU (for the end device) is used, and there is no communication at all about power (as is the case for active PoE: on/off-voltage).

[Erik Slagter]

That is "legacy", 802.3af requires active handshaking. I don't see much "legacy" PoE nowadays.

[Rob van der Does]

I do, and far from legacy. Simple (cheap) devices and DIY PoE-conversions.

See e.g. https://www.google.f...0k1.TDm6tzrYrgI and http://www.tp-link.c...TL-WA801ND.html

[KennyL]

PoE I have (ubiquiti injector) is passive and always on. I did some research, and it seems that ethernet specs require rj45 ports to be magnetically coupled and handle a lot more than 24V? https://electronics....tically-coupled

[Erik Slagter]

Then it's no official PoE 802.3af.

 

The "magnetically coupled" is the transformer I talked about earlier. It should be able to withstand up to about 2.5 kV.

 

And also, PoE is not 24 V but mostly 48 V.

[KennyL]

Can we assume that VU+ uses transformer/magnetic coupling on its RJ45 ports?

I found the RJ45/USB/USB socket that is used by VU+:

http://www.fu-yao.co...IGHT-ANGLE.html

At first I thought Dielectric Withstanding Voltage: 100VAC Min. means some type of protection, but usb-only socket has exactly the same spec.

http://www.fu-yao.co...pe.html?CID=8_2

Edited by KennyL, 24 June 2017 - 02:23.

[Erik Slagter]

Transformer decoupling is required by the ethernet over twisted pair standard.