DIRECT LIGHTNING STRIKES
The users of electronic equipment, telephone and data-processing systems must face the problem of keeping this equipment in operation in spite of transient overvoltages induced by lightning and/or switching surge events.
There are several reasons:
- Electronic components are more sensitive and more vulnerable
- Interruptions in service are unacceptable in modern life
- Equipment is now installed directly in the field and are exposed to larger and more frequent disturbances
Investigated since Benjamin Franklin's first research in 1749, lightning has paradoxically become a growing threat to our highly electronic society. Lightning is a natural phenomenon, defined as an electrical discharge between two zones of opposite polarity, the most serious for equipment occurs between the cloud and the ground. The result is a current lasting from 20 to 350 microseconds or more and can generate significant side effects such as transient overvoltages. These effects which include disruption and degradation to equipment can be more damaging than the discharge itself. The development of more powerful yet sensitive electronic equipment results in their susceptibility to damage from surges. The lightning constitutes a real threat for critical equipment but also for contracting professionals or even private individuals. The technique used to protect against lightning consists of capturing the lightning discharge, diverting it from its intended target and safely conducting it to ground.
Lightning protection systems that employ a lightning down conductor or a faraday cage will save the site, however your electronic equipment will not be immune from its side effects.
DIRECT LIGHTNING STRIKES
Direct strikes or conducted surges, at the moment of the lightning discharge, produce an impulse current flow that ranges from 1,000 to 200,000 amps at its peak with a rise time of only few microseconds. Since these events are highly localized to the structure, the surge effects are generally only a small factor when considering the potential for damage to electric and electronic systems.
The best protection for lightning is still the use of standard lightning rods (Franklin rods) connected together by a network of conductors tied to the earth ground. This forms what is known as a Lightning Protection System (LPS). LPS are designed to capture the discharge current, conduct it to a particular point then safely to the earth. The most commonly implemented standard in the United States is UL96A and it's UL Master Label Certification. A critical requirement of this certification is the mandatory installation of surge protectors on each connected network including all power and communication systems.