Question : Problem: Power over Ethernet Distance

How far can POE go? Does using cat5 or cat6 make a difference in the length or data loss?

Answer : Problem: Power over Ethernet Distance

Hello pghzooit:

POE distance depends on amount of current consumed by end device, voltage that it requires, the voltage of the injector and the voltage drop along the cable.

Since CAT5, CAT5e and CAT6 can be made from 22-24 gauge wire, the resistance and total distance for POE varies greatly.  Also, POE technologies have huge variations, from straight DC to various AC tricks, so any length figure is only meaningful based on a specific technology and vendor's equipment.

Simplistically, CAT5e cables typically use solid (although patch cables use stranded) 24 gauge wire and the insulation is rated for 50 V service (maximum).  The TIA rates its current carrying ability as 360 mA but the voltage drop will depend on the temperature, condition of the wire (bent or stressed wire has a higher resistance and hot wire also has a higher resistance).  Despite this, the nominal resistance of 24 gauge wire is ~ .03 ohms/foot, so the voltage drop at .36 A is about 1 V/100'.  

The whole setup is very non-standardized but there is much effort in this direction.  Here's a useful (?) reference on POE:

http://www.altair.org/labnotes_POE.html

And here's another one supported by a vendor:

http://www.hyperlinktech.com/web/what_is_poe.php

and finally, a Wikipedia (?) citation:

http://en.wikipedia.org/wiki/Power_over_Ethernet

Finally, to answer your first question, a 'rule of thumb' is 300' for most POE using 48 V injectors but it is honored more in the breach than the observance.

wb