The Threat

Sources of Overvoltage Surges 
 

Lightning:

    In addition to the obvious problems a direct strike will cause, the induced voltages can damage overhead and underground lines, as well as the telecommunication systems, electrical equipment and cable TV some miles away.
     
Electric Mains:   The induced surges caused by the switching of electric motors and other interference.
     

Static Discharge:

   The peak voltage can be as high as 35,000v and cause data corruption and damage to printed circuit boards and components.
     
Electromagnetic Pulse (EMP):   A nuclear detonation of one megaton 100 miles above the surface of the earth will not cause any damage to life or property.   However, the energy produced would cause a nuclear electromagnetic pulse (NEMP) that would damage unprotected electronic circuits over an area as large as Europe

 

What Needs Protecting?

 Not only buildings and equipment need protection. Personnel, Software and computer stored data are also at risk which involve a company in heavy expenditure if they are not suitably protected against overvoltage transients.

 

The Basic Types Of Protection
 

Lightning Conductors:

   These are installed on buildings and structures after calculations have been made considering various parameters including soil resistivity.
     
Gas Discharge Tubes (GDT’s):   This device is gas filled and usually consists of an envelope made up of two or three electrodes separated by ceramic insulation.   It operates like a switch diverting surges and preventing them reaching equipment.
     

Varistors:

 Metal Oxide Varistors operate by clamping a surge at a specified voltage.
     
Transient Voltage Suppressors: These devices operate by clamping voltage transients at specific values.
     
Hybrid Arresters:   These devices are made by joining GDT’s and Varistors or Transient Voltage Suppressors together to obtain the different benefits of each in one package