We have small local network at home. As it is hobbyist LAN, the cables goes in various strange ways- on the trees, near power lines and etc. We are using FTP ant unshielded (!) UTP cable. In summer, we have few thunderstorms every year. And every year we have dead switches and LAN cards. One year, lightning even managed to burn mainboard in my computer.
Lets look ant the schematics of realtek based UTP switch:
And now look at the photos…
Look ant 75 ohm resistors…
And take a look to the color of shield near the damage. It is not the smut from the flame. It is color of over heated steel. This means that there was electrical arc between resistors and metal frame. The ports are dead, but the device’s other ports are working fine.
I think, that the unshielded cable was connected to these ports and after lightning stroke there was minimum 2..3kV overvoltage here. The blue 2kV capacitors are undamaged. It is not the direct hit! If it was direct hit of the lightning, there would be big black hole here. The overvoltage was from inductive interference from distant lightning.
Using used details from scrapped telecoms equipment I’ve made very simple protector. I am using it for more than year and there was few nice storms this summer. The switch was killed, but my computer’s LAN card is OK. In the next weblog message I’ll show the schematics. It is very simple and LAN is working at 100Mbit/s without any problem.