Ethernet surge and protection

Question

I recently worked with a client who experienced a transient on their Ethernet cabling. As you can see, no actual PCs were damaged, only the Ethernet cards of some machines. We don't know where the surge originated.

Can anyone explain how the damage could have occurred as shown? I thought Ethernet had isolation transformers at each connector which would likely stop surges from propagating.

Damaged nodes are highlighted in red. Note that main network stack in the center has AC mains surge protection.

Also note that the main network switch was completely destroyed - i.e. would not even power on.

As a follow-up, would Ethernet surge protection hardware be helpful for preventing this type of damage? If so, where in this diagram should it be installed? main stack or at each PC?

Thank you!

Answer 1

Is there a potential difference between the lines supplying the power sockets? In the UK, a large building or a group of buildings in a complex may have three different phases supplying the 240V (different phases to different parts of the building), with a possible 415V potential across different areas. A surge or earth fault could have been to blame.

Answer 2

I would think the surge entered through in the ground of the big switch, as the other equipment in the rack shares the same ground that equipment was equipotential and was not damaged, the surge then radiated as a common mode signal out through the network cabling destroying two directly connected network cards and hitting two switches.

this sort of damage needs kilovolts, and to get kilovolts on ground it takes a lightning strike. or a shock line, did the did the big netgear switch fail spectacularly?