We have an outdoor network camera powered via POE from a rack through around 125' of cat6. We also have 18/2 run from the rack to the same location of the camera. Our goal is to add additional POE cameras (perhaps 1 or 2) at various locations within 20' of the first camera. No other wiring and no power is available at the camera location.

My thought is to add network capacity by running the cat6 into a POE switch and then power that switch using the 18/2. (Either the switch would be outdoor rated, or more likely we would use an outdoor enclosure.) Could I possibly take the manufacturer supplied power cord, splice in the 18/2 and be done with it?

For the sake of example, let's say the switch I'd like to use is the Netgear GS305P switch:
[Link: images-na.ssl-images-amazon.com]

My guess is that this will not work because of voltage drop (and perhaps other electrical changes/anomalies) introduced by inserting 125' of 18/2 into the manufacturer supplied cord. Does anyone know for sure? Or, are there network switches designed to be powered this way? Any other ideas?

you could use something like this. It can be POE powered and outputs POE as well

[Link: veracityglobal.com]

Thanks, I'm familiar with products like this, but I don't think they will give me the power budget I need for 2-3 cameras with PTZ. (I tried looking at the link but it seems the site is down at the moment.)

Depending on the wire type, the electrical code would take a dim view of running full line voltage out to the site. One solution would be to use a variable voltage DC supply and increase its output to compensate for the voltage drop. An interesting, yet kludgy approach, would be to run low voltage AC out to the site and use a step up transformer at the site. In this scheme the network switch's own power supply would be tolerant to supply voltage variations.

We use these hardened PoE switches from Trendnet TI-PG62. They are powered by a 48V DIN style power supply. Never ran 125' of 18/2 between the pwr supply and switch, but I think it would likely work.

In your example, all it takes is a little simple math.
Switch is powered by a 48VDC power supply, that can supply 1.25 amps. At a distance of 125 ft over 18 awg copper, the maximum voltage drop would be 2 volts at full load.
Here is a simple online calculator you can use:
[Link: calculator.net]

It should work fine.
But for + confirmation, you can set this up on a test bench real quick and verify proper operation.

+1

These switches also have a range of acceptable voltage supply, so should be more forgiving than your average switch. Calculate your drop and size appropriately.

Thanks, the Trendnet TI-PG62 looks promising.

We did a similar thing with this:

[Link: cdw.com]

Outdoor, under eave? Any closer power, in the attic, or nearby, closer than 125'?

I know you said not at the camera locations.

I'm testing this out on my bench now, and so far so good. The switch runs from 48V-56V, and the power supply (sold separately) can be adjusted to produce 48V over 150' of 18/2.

Everything is working. I'm just letting it run for a couple of days with a camera and WAP plugged in to make sure it's solid.

Thanks again for the tip.