Protecting Your Laptop During Thunderstorms: Lightning & Ethernet Risks

[Rach3]

Suppose I have a laptop on battery power, connected to a network router which is AC powered, during a thunderstorm. Will a voltage spike at the router cause any damage to my laptop NIC?

 

[chroot]

It certainly could, but it's not very likely, either.

A lot of devices would have to fail in some very specific ways (the wall transformer, the regulators on the router's circuit board, the drivers on the transceiver IC, etc.) to permit a large voltage spike onto the ethernet cable. The majority of the time, the lightning strike would essentially vaporize one of these components, creating an open circuit that would limit its damage. This could be called "failing open."

Futhermore, the actual ethernet line drivers in your router are on an integrated circuit. They connect to the outside world through very tiny gold bond wires, each smaller in diameter than a human hair. They cannot carry much current at all before vaporizing, so it's not very likely that a significant amount of charge could be pumped through the driver before it fails open.

On the other end, your laptop's NIC has an ethernet transciever with a lot of ESD protection built into it, including snap-backs or clamps and beefy diodes. They would probably happily absorb any voltage spike that comes through the ethernet cable, given that the transciever on the other end is rather self-limiting -- it would fail open before it could transmit much charge.

- Warren