Surge Arresters: Are they the Solution?

With all the electronic and electrical equipment used in our day to day lives we only realise how much we rely on these systems when they suddenly are not working. This always seems to happen at the most inconvenient time and it is normally at this time that we discover those safety measures we put in place to not work.

Lightning and surge protection is just one of these nasty surprises that can be avoided if correctly installed. Unfortunately there are many ignorant as well as unscrupulous contractors and suppliers who will supply the client with the incorrect solution for their specific problem.

The most common error is that people believe that if the building has external lightning protection installed on the building then the electronic and electrical equipment within the building will be safe. Unfortunately this is not true and in actual fact the SANS 10142-1:2003 states tgat uf external lightning protection is installed on a building then additional internal lightning and surge protection to the building itself (structural protection) and thus does not offer any protection to the equipment within the building. It does help in offering a controlled discharge path to earth and thus can prevent the lightning strike choosing its own dissipation path to earth via the electrical and electronic equipment.

One of the most basic principles of electricity is that when current flows through a conductor it will generator and electromagnetic field around that conductor. The principle of a transformer is that the change in magnetic field of the primary winding cuts through the secondary winding inducing a voltage in the secondary winding. The lightning bolt is nothing more that a large conductor (primary winding) with a massive electromagnetic field around it which can extend for up to 1 kilometre from the actual strike. This means that all the electrical and electronic equipment (secondary winding) will be exposed to a massive expanding magnetic field during the strike and then a second massive collapsing magnetic field once the strike is over. If lightning were to strike within 100 meters of your equipment the induced voltages could be high as 2000 volts per meter. This is the very basic principle as to why equipment suffers damage during a lightning storm even though it may not even be struck directly.

The actual chance of a normal house in South Africa being struck directly by lightning is less than once in 25 years but they will be exposed to the effects of a lightning strike up to 10 times per year. Luckily due to natural screening and shielding offered by buildings, steel conduiting or trunking and cable screens these effects are greatly reduced. Unfortunately with the greater use of plastic trunking, plastic conduiting and unscreened cables (UTP cabling) the natural electromagnetic screening and shielding is lost.

Taking the above in consideration, you would only insist on installing external lightning protection if you were worried that your building was in danger of taking a direct strike but in addition you would insist on adequate screening and shielding, correct earthing especially potential equalisation bonding and surge arresters.

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