Update: I'm thinking that for some reason the switch is reversing things because of MDI/MDI-X. Not sure why, since the cables are straight....
Pro Focus LLC | 02/27/16 03:21pm
Sometimes people confuse electron flow with polarity. This could be the case here?
Update: Now offering from $0.70 to $1.05* in voting credits for anyone who can provide polarity information for their switch (while powering a device).
No photo required, just list the brand/model and the polarity of pins 1-2 and 3-6.
*Must make small joke to be eligible for funny bonus.
Heres a decent "whitepaper" that has different information from a manufacturer that only focuses on power...
That document calls out 1/2 as Negative and 3/6 Positive. Which falls in line with what you are reading.
Other things I read actually stated that there is no "standard polarity" defined in the 802.3 standard, which I dont really believe, but its out there.
Thanks Sean, that's an interesting document, and the first I've seen that calls out negative on 1-2.
...its possible that you end up reading different polarities depending on the manufacturer of the PoE chip in the PD unit.
I don't think you would get different polarities by changing the PD, though. Changing PSE's can definitely do it though.
According to the spec, the PD has to have a bridge rectifier on input, which makes it work regardless. This was done in case a crossover cable is in use.
So why do I care? Because, I am working on a network analyzer and thought I could determine whether a crossover cable was in use by the polarity.
But apparently, regardless of the standard, a single polarity cannot be counted on in the field, so now it is nothing more than just a curiosity of why some ended up that way.
For the record, I have tested the following brands of PSE's
- Netgear 3-6 +
- Dlink 3-6 +
- TPlink 3-6 +
- Linksys 3-6 +
- Everfocus 3-6 +
- Cisco 1-2 +
- Allied 1-2 +
- Silvertel 1-2 +