Power over Ethernet #2

It would be great to be a kid again, to be able to write wonderfully dangerous material and have it spread world-wide without a care. This is my opinion of two of the Do It Yourself (DIY) Power over Ethernet (POE) hacks on the Web. The most famous one, in terms of Goggle rating, is offering some basic ways to disable your phone service and start fires. Yes their offering might work, but I have a few problems with their recommendations.

Site #1

First they recognize that the middle two conductors, Blue/White pair, are sometimes used for phone service. They postulate that the application of power to these might cause problems. What they didn't point out however that the connection of their circuit to a live phone would immediately kill the phone service. Why, the Blue/White pair are tied together, shorted. With any modern phone system this would generate trouble in the form of no dial tone. "Gee, Mom how was I supposed to know that my new invention would result in the phone company responding with a hundred dollar service call?"

Within their example calculations you find an example of 28 guage wire carrying 2 amps. The maximum for this size wiring, in free air, inside a chassis, is 1.4 amps. (By way of reference, National Fire Prevention Association Bulletin 70.)

A more dangerous recommendation is the illustration of connecting a wall wart power supply to their cabling without a fuse! If a fault occurred the current would be only limited by whatever unknown is within that power supply. So say this cable were to be installed within a wall or attic space, a misplaced wire staple or kink in the cable run causes a near short. Things heat up and "Gee Mom how was I supposed to know that my new invention would leave us homeless?"

Site #2

Another site, linked from Site #1, shows how to raise the supply voltage to compensate for the wiring voltage drop. This is a really good way to burn out a modern network device. Why, because if the reader follows the instructions and powers up the circuit. Then plugs in the powered device it will see the greater open circuit voltage rather than the calculated voltage. Additionally this over voltage, if it doesn't immediately destroy the device, will surely shorten it's life. "Gee Mom our wireless access point just stopped working, maybe we can return it under warranty."

The most dangerous recommendation is the calculation of voltage drop in a wire run. The numbers seem accurate, but, they allow you to enter currents in excess of the fusing currents for copper wiring of that given guage. Granted the author does try to warn the user with a cautionary note about watts per foot. Again, "Mom you did say you wanted to remodel."