It’s the season for lightening storms in much of the northern hemisphere. Here in Clearwater, Fla., we’re really aware of the risk of damaging surges since some pretty intense storms come through almost every afternoon and evening.

Uninterruptable power supplies (UPSs) and surge protectors are standard countermeasures, although a poor-man’s risk management strategy is to simply unplug electronics when the storms come through. Putting equipment on power strips and turning those off can make it a bit more convenient. Working on your laptop on battery power (with no wired network connection) during storms is a pretty good idea too if you just CAN’T get off the computer (guilty here.)

Johannes Ullrich at SANS in Jacksonville, Fla., posted a great diary entry about his experience with equipment damage from lightening-induces surges. Apparently, lightening does strike the same place twice, since he describes two experiences:

“The damage I had, in particular in the last storm, affected exclusively network equipment and networking interfaces. I assume that the surge entered the network. I lost two switches and the wired network interfaces in two PCs. Otherwise, the PCs work fine. So far I had not used any network surge protectors, but now started to use the surge protectors provided by the UPS. This appears to work fine, but in some cases, the network now works as “half duplex” and no longer in “duplex” mode. I looked into stand alone network surge protectors for some devices, and it turned out to be a bit hard to find one that supports gigabit ethernet. But they are available. The UPS network surge protection is only supposed to work up to 100 Base-T but synced fine at Gigabit (no duplex).

“A thunderstorm a couple months ago, caused some “interesting” damage to my cable modem. I was only able to upload 1MByte in a single connection. This was very weird as it also applied to connections inside VPN tunnels, the cable modem shouldn’t really ‘see’ what was happening. But sure enough, swapping the modem fixed the problem. I added a surge protector for the cable line as well…”

“Couple other hints:

– do not plug surge protectors into a UPS. If the UPS runs on batteries it will usually generate a steep sine wave which may destroy surge protectors (in particular tricky to find power strips without surge protector)
– do not plug a UPS into a UPS (same reason as above)
– lightning damage can be subtle. None of my equipment has any visible damage
– proper grounding of all lines entering the house is important (around here, I find that utility companies are pretty good about that)
– once the power is out, turn off the main fuse to the house. But be aware the main fuse can be hard to “flip”. Depending on the nature of the outage you may have some surges and unstable power until the damage is repaired (if you want to know when power comes back, just flip all the individual fuses other then one or two that only power lights)”