Don’t let lightning spoil your broadband experience
Are you protected? The question sounds a bit like an advertisement from a condom factory or even an insurance company. It is however a serious question because contrary to popular belief lightning strikes more than once and those cheap surge plugs and power strips you buy at the supermarket or hardware store offer very little protection.
Are you one of those guys who is woken up in the middle of the night by an approaching thunderstorm and just about break your neck to get to your study to rip out the mains plug of your PC, modem and whatever else have you? Not such a bad idea but it does not mean that your equipment is totally protected when a heavy thunderstorm is nearby. You are asking but why? There is then no physical connection to the mains or phone line!
Boet it is called induction!
A nearby lightning strike sets up a magnetic field. Even with the PC disconnected from the mains the connection between the various sub-systems connected to your PC form an inductive loop. Like a transformer, as the magnetic field crosses the inductive loop a current is set-up that can reach many times the operating voltage of the system and cause severe damage. So even with no physical connection to the mains or telephone line your equipment could be damaged.
So you turn over and go back to sleep because you have a surge plug fitted.
Consider what happens when lightning strikes the ground or an object that is connected to the ground. If one could measure the potential in the ground at the instant that lightning strikes, the potential where the lightning enters the ground is in the order of several hundreds of thousands of volts. Further from the point of entry the potential will drop off until at some distance from the point of impact the potential drops to 0V.
Consider the two points. They are like the terminals of a 500 kV battery (if there was such a battery). Connecting a conductor across the imaginary terminals that have a much lower resistance than the ground path, the larger current will flow through the conductor. Using ohms law with two resistors in parallel, the resistor with the lowest ohm value will carry the larger proportion of the current.
It is this principal that causes so many deaths amongst people and livestock around the world every year. A golfer on the course near a lightning strike provides a lower resistance path between his two legs, that are a little distance apart, and is thus subjected to a high current flow through his body.
If we however earth equipment near the point of strike and again other equipment some distance away and the two earthed sites are connected through a telephone or data line, there will be a difference in potential that will be equalised through the lowest point of resistance, which will be through the equipment causing severe damage.
Can I win this scourge? Yes by fitting proper protection.
The ideal solution is to create a surge protection platform. All incoming and outgoing lines are protected by an appropriate surge arrestor. Each arrestor is bonded on an earthed platform with very short bonding wires or even directly mounted on the earthed platform.
It’s that long green wire that is attached to some surge protection devices so don’t coil it up and keep it together with a cable tie, it is the ideal transformer to catch induced current from a nearby strike. Cut it as short as possible.
There are many reputable companies that can give you advice on how to sleep soundly though a thunderstorm. Some have developed units that make it easy to create a protection platform for your PC. Some are so confident that they offer free insurance.
Lightning and broadband – give your views
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