How does lightning damage equipment?

  Nosmas 23:24 17 Jun 2003

This afternoon we had a very bad thunder and lightning storm. Becoming concerned at the intensity of the lightning flashes I decided to unplug my telephone connection from the wall socket as I have no surge protection in place. Before I reached the socket there was a brilliant flash of lightning and my ADSL USB modem emitted a sparking sound, and that was the end of my modem.

Nothing else on my system seems to have been affected. I thought that maybe the USB circuits may have suffered, but the second USB port seems to be OK as I was able to download some images from my digital camera. Is there any way of checking if I have suffered any other damage?

One thing that puzzles me is how the lightning causes the damage. If my house had been struck I am sure I would have been aware of it, and all the telephones seem to be working OK. Can someone please explain exactly what happens to burn out something like a modem? Incidentally my 56K modem seems to be OK as I am using it to access the Internet (oh so slowly!!)to make this posting. The only thing I have noticed is that I now can't hear the beeping when the modem dials out.

  woodchip 23:31 17 Jun 2003

Hardware will work or it will not, Just like a fuse the item ether goes open circuit or is burnt out

  woodchip 23:32 17 Jun 2003

PS it could just as easy been your computer printer scanner or even you, if you allow to run in a storm

  beeuuem 23:44 17 Jun 2003

When lightning strikes, even some distance away, your earth connection is no longer 0 volts as it has had a large voltage potential applied to it.


A lightning strike "cloud to ground" or "cloud to cloud" produces electromagnetic fields that can induce voltages on the conductors (wires) of AC circuits as well as data communication lines, phone lines, or transmission cable.

Lightning ground current flow results when a strike that discharges to the earth couples into common ground impedance paths, causing voltage differential across the ground grid and between ground-neutral or ground-line circuits. In short, the reference ground (supposedly zero voltage) is elevated a few milliseconds, therefore creating a large voltage difference between ground and the incoming power and/or data lines.

Direct lightning strikes, to high voltage primary circuits, inject high current into service transformers and produce voltages either by flowing through ground impedance or flowing through the surge impedance path of the primary conductors. Direct lightning strikes to secondary circuits may exceed the withstand capability of equipment and conventional surge protection devices rated for secondary circuit use.

Lightning causes utility company primary gap type arrestors to fire, limiting the primary voltage but coupling transients through the capacitance of mains, transformers, and injecting surge voltages in addition to those coupled by normal transformer action. Power company protective devices limit life threatening overvoltage; however, they create a number of damaging transients in the process, that may damage electronic equipment.

Lightning does not have to be close to create high voltages in any line (power, neutral ground, or communications). The effects of nature?s electricity induce voltages into all lines for miles around. These voltages near the lightning strike can be catastrophic, the induced voltages a mile away can cause high voltage that can create electronic system failures, and a few miles away can stress electronic equipment causing delayed (latent) failures.

  beeuuem 00:17 18 Jun 2003

You haven't seen lightning till you've lived on the Highveld. And trying to protect comms and data equipment networks teaches you more than you ever wanted to know about lightning protection and how feeble it can be!:-))

  Nosmas 00:38 18 Jun 2003

My thanks to everyone.

beeuuem your very full explanation was I fear a bit above my head in places, but I get the general drift! I must say I was surprised to learn that things can be affected even though they are miles away from the strike.

I have ordered a replacement ADSL modem and also a Belkin UPS which has Automatic Voltage Regulation and surge protection which I hope will prevent a recurrence of such damage, despite beeuuem's comment as to the feebleness of protection.

One final question - Was it coincidence that my car's alarm went of when my wife attempted to start it only a few minutes after the flash that ruined my modem?

  beeuuem 00:57 18 Jun 2003

The feebleness referred to African thunder storms which are bigger and better- depending on your point of view - and surface cable networks where the strike can be many miles away and travel down the wire with dire consequences .
I use a Belkin surge protector here (UK) and have never (touch wood!)had a problem with over voltage on my PC. It should give you all the protection you need - and it does come with a guarantee.

  beeuuem 01:03 18 Jun 2003

I've seen it close but nowhere near as close as you. You were fortunate it wasn't any closer. Having seen what it can do do to metal, cable, etc. which are all more substantial than me, it is an experience I'll happily live without.

  Nosmas 23:35 18 Jun 2003

Well this post has certainly produced some interesting replies - thank you everyone for your contributions. Until yesterday I had not appreciated just how easy it is for lightning to cause instant irreparable damage, even without being in the path of a "direct hit". I have learnt an expensive lesson, so perhaps others reading this post will benefit from my misfortune and be persuaded to take some sort of preventative action to avoid becoming victims themselves.

  woodchip 23:42 18 Jun 2003

I learned my lesson 10 years ago it did my cordless phone in. It would work, but would not ring after the strike.

This thread is now locked and can not be replied to.

Elsewhere on IDG sites

Samsung Galaxy S10 review

Butcher Billy's Black Mirror artwork is coming to vinyl for the first time

Is the Apple Store down? What's Apple launching?

Comment modifier le DPI d’une souris ?