Habilitar PoE en Teléfonos Cisco 7940

A continuación les dicto la línea de como habilitar PoE en los teléfonos Cisco 7940. Este es un tema que resolví al interior de mi compañía hace un par de años atrás, pero que volvió a mi mente hace un par de días cuando tuve que enseñar a un colaborador como construir el cable para que el teléfono soporte los beneficios de PoE y no tener que conectar una fuente de poder y estar sujetos a los cortes de energía.

Basta simplemente con cambiar los pines 4 por 7 y los pines 5 por 8 en el cable ethernet.

Adjunto toda la literatura al respecto:

It was recently brought up on the IRC channel that the 7940 and 60  phones from Cisco do not support the IEEE 802.3af Power Over Ethernet standard (which you have to pay for). At first, I didn't believe it, so I grabbed a 7960 and tried it with a standard 3COM POE injector and found it to be true. Only the new 7970G phones will work with the IEEE 802.3af standard.

But hope is not lost! Denon suggested that they would work if you simply reversed the polarity of 2 of the pairs of wire. He said that by swapping 4 with 7, and 5 with 8 you could use a standard POE injector to power the phone.

Since I had a crimp tool and some cable laying around, I gave it a whirl and it works. If you aren't familiar with making cable, don't try this at home.

Basically, you just wire one side of the cable as standard 568b and then reverse 4 and 7, and 5 and 8 on the other side. Then, simply plug your Cisco into a standard POE injector, like the 3CNJPSE ($23.00) and voila! Your phone works.

I've included color mappings for convenience, and you can reference the following fine site for pretty pictures:

Damin's POE Cable

568b
________________________________________
1 Orange - White
2 Orange
3 Green - White

4 Blue

5 White - Blue

6 Green

7 Brown - White

8 Brown

Cisco Side
________________________________________
1 Orange - White
2 Orange
3 Green - White

4 Brown - White

5 Brown

6 Green

7 Blue

8 White - Blue

P.S. This hasn't blown up my 7960 yet, but I'm not an electrical engineer, therefore, use at your own risk and I am DEFINITELY not responsible if you flip the wrong pairs and turn your unit into a smoking pile of rubble. If you are that concerned and/or inexperienced with making cables, look on Ebay and get a used Cisco POE injector, or Power supply. They are  relatively cheap nowadays.