Need for Three Levels of Surge Protection to Reduce Cost of Destruction by Surges


PRIMARY PROTECTION is provided at the mains service entry point to protect your electrical network at the highest level from surges caused by lightning, transformer taps, power stations, sub stations, distribution faults etc.


In addition to these, surges can be generated by your own factory equipment and office equipment such as air conditioners, elevators, pumps, power tools copiers etc to varying degrees. Power cross faults or switching operations of the factory next door causing surges are also common. Cables running parallel to structural metalworks which might act as a lightning conductor and induce surges in the cables. SECONDARY PROTECTION is provided at supply distribution boards to handle such internally generated surges up to 10 kA.


While the primary protection will limit the maximum incoming voltage to 600-700V, resonance within the installation can produce a’ ringing’ voltage, which can rise to as much as 2kV.


Components and circuits of modern sensitive electronic equipment such as computers have become smaller over the years and are very vulnerable to the effects of even small surges. Even a simple act of switching on a florescent light could generate a high transient over-voltage due to the stored energy of the choke that could damage circuits or data or both. Centralized switching of large number of florescent lights is more likely to produce harmful transient than staggered switching. Therefore, ‘FINE PROTECTION’ which would not cost a lot compared to the cost of computers/loss of data and specially the loses due to interruption to production or other processes is a very effective method of protection.

Finally, a protection system that satisfy your organizational needs should be designed considering the cost of the SPD system against the cost of damages that it would prevent:


  1. Cost of replacing damage computers and/ or other equipment,
  2. Loss of data, the value of which could be immeasurable,
  3. Loses due to interruption to production or other processes.


  • BS6651 Appendix C and most other standards defines 3 levels of protection.
  • Loss Prevention Council of the UK recommends the use of protection methods to BS6651.
  • International Copper Association which monitors the copper industry says “75% of all computer failures are caused by power quality problems”.