We are using passive PoE injectors and long ethernet cables.

Below a reference table for the voltages ranges of the hardware we use:

Item	Low	High	Max Consumption
alix2d13	7V	20V	5.0W
NS5, M5, M2	9V	24V	8.0W
MS M2-Loco	9V	24V	5.5W
Bullet5M	10V	24V	6.0W
airCam	9V	24V	2.4W
apu1d4	12V	12V	12.0W
RB260GS	6V	31V	6.0W

You want the Voltage to be as high as possible, causing your current to be as low. This in general makes transport over UTP wires more effient (higher voltage = less loss) and causes your adapters to work more effient (AC->DC adapters tend to be more effient and last longer if you keep the voltage as high as possible).

We aim to get between 18V-20V to our node, Make sure to keep track of your input voltage ​Calculate when using long cables.