The function of a lightning protection system is to intercept, conduct and dissipate to ground a lightning discharge that might otherwise strike a vulnerable part of the building and equipment within it.
Why lightning protection system is important?
It will prevent loss of human life, service to the public, cultural heritage, and economic values (eg. structure and its content, service, and loss of activity).
Where will be the possible location or areas that the lightning strikes?
It can be direct to the building or structure, near it, to an electric line, or near the electric line.
What are the consequences of lightning strikes or flashes?
- Injury to living beings due to touch and step voltages.
- Physical damage (fire, explosion, mechanical destruction, release of chemicals) due to lightning current effects including sparking
- Failure of internal systems due to LEMP or Lightning Electromagnetic Pulse
This is in one of Refinery in USA which was caused by Lightning as per report
There are two international standards that established Lightning Protection System, the NFPA and IEC.
For NFPA, it is NFPA 780 while IEC has IEC 62305. NFPA 780 mostly applied to American requirements while IEC for European countries.
The IEC is also being applied in America. It is acceptable if the installer is a UL-certified installer and it will pass inspection by a UL LPS inspector.
IEC 62305-3 is the main part that established the lightning protection measures to be placed. This part defines the requirements such as the "air termination", "horizontal/down conductor system", "earth termination system", "separation distance", "test link" and "lightning equipotential bonding".
See the figures below for a visual point of view.
Air Terminal and Horizontal/Down Conductors Installation
Test Link
Earth Pit with Electrode
Some studies suggest that IEC 62305 is more expensive than NFPA 780. According to studies, materials required for an IEC 62305 installation are 50% more than the NFPA 780 counterpart, with the same building applied. The installation cost for IEC is cheaper which is about 30% cheaper than NFPA 780. Overall, IEC 62305 installation has more than 3% cost compared to NFPA 780.
Installation based on IEC 62305 depends on some elements such as lightning parameters, rolling sphere radius, the distance between conductors, minimum length of electrodes, separation distance against dangerous sparking and all of it will be according to the Class of LPS applied.
The characteristics of an LPS are determined by the characteristics of the structure to be protected and by the considered lightning protection level.
With regards to the difference of air terminals for each standard, NFPA 780 requires support must be added at not less than ½ height for air terminals over 24 inches.
Sample of Rolling Sphere (Courtesy of Lightning Protection (cadsolutions.com.au))
3D Generated Resultant of Rolling Sphere Method ((Courtesy of Lightning Protection (cadsolutions.com.au))
With regards to the horizontal/down conductors, NFPA 780 sticks to 30meters spacing (regardless) while IEC 62305 will have different spacing according to LPS Class.
In summary:
"IEC 62305 risk assessment is normative, NFPA less detailed risk assessment is informative."
"IEC 62305 risk assessment results in four LPS classes, with air termination, down conductor, and earth termination systems dependent on LPS class."
"NFPA 780 risk assessment results in a go/no go one size fits all LPS, with a rolling sphere equivalent to IEC LPS Class 3."
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