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      ||  9V || 24V ||  8.0W ||
|| Bullet5M || 10V || 24V ||  6.0W ||
|| airCam   ||  9V || 24V ||  2.4W ||

Make sure to keep track of your input voltage [http://blog.fosketts.net/toolbox/power-ethernet-calculator/ Calculate] when using long cables.