POE - question about "compatibility"

Ok, compatibility isn’t the right word.

Couple of questions:
My arduino (ether10) has POE. But that is a power INPUT - right?
There is an arduino POE “HUB” thing Jaycar sells where there are 4 CAT-5 ports which all have POE.
I therefore read that as:
If you have 4 Arduino cards with Cat-5 ports, you can power them all from this and also have them networked.
That way you save needing 4 power supplies, just one “central” one which feeds all 4 boards.
So it begs the question:
Say I have less than 4 cards, and want them on their own little network, BUT want them to be connecte to my “larger” network which isn’t always on.
I have a big hub/switch/thing with a spare hole for this other “Arduino bunch of cards” to connect.

Will there be a problem if this device also has POE and I plug a cable from it to the Arduino POE card?

It is still "work in progress but may be happening in the future. Thought it better to ask now so I can understand any problems before they really happen.

Sorry, P.S. My larger LAN is a GIGABIT network with POE - well I think it has POE. The power supply may be dead but it says it has POE.

I'm assuming you talking about http://www.jaycar.com.au/productView.asp?ID=XC4254&keywords=poe&form=KEYWORD that's a non standard midspan injector(aka no 802.3af) your etherten supports either, though it seems anything more than just running 12v over the unused pairs requires an extra board. Mind you that part from jarcar is not a hub/switch it takes 4 ports on your networking kit to connect but it does not care if they are poe as 802.3af will not work through it. If you want it to run while your main kit is off a cheap 5 port 100bt switch would do. Mind you non 802.3af poe injectors are a couple of bucks on ebay it's literary just wiring up a dc power supply to unused pins and can be done by clipping those wires and connecting them to a 2.1mm jack or similar.

Standard PoE senses the end device for compatibility. There's a standard protocol for PoE-powered devices that defines resistance between certain pins. If this resistance is there, the device supports PoE, and the switch (or injector) will apply power. (There is further intelligent negotiation for power consumption classes, but that's a different matter.)

Non-standard PoE just dumps power on the pins and hopes the device on the other end is expecting it.

If you use an injector (of any type) or another hub between the Arduino and your PoE switch (assuming the switch is standard PoE), it will not apply power unless the injector/hub has "requested" it via the pin resistance. So it's safe.

Yes the Jaycar reference was the thing at which I was looking.

So reading the first reply, that board ONLY does POE and isn't a HUB. Drats! (kinda)

Ok, it seems doing it that way will be more complicated than I thought.

I won't persue it.

No worries.

Thanks for the replies though.

Networks are also very new to me. Though I do have a gigabit network, I kind of found the switch in a bin, and semi-fixed it to work. (It's a D-link so basically it is junk, but as some of my devices support gigabit, why not use it?)

So just to check again: The arduino Ether10's POE is a power INPUT.

Yes, but according to their site, to use the ratified PoE standard, you need the appropriate regulator board add on. (Built-in support is limited to low-voltage power injection.)

BTW, those D-link Gigabit switches aren't half bad. I've serviced a few sites that used them, and even recommended and installed a few myself. They're dumb, and certainly no Juniper EX. But, they work!