Surge Damage and Risk
Today's buildings are inevitably interconnected by various cables for electricity or communication.
There are numerous signal cables in the building, which include telephone lines, LAN cables, antennas, and CCTV camera circuits connected to phones and faxes.
If a building is struck by lightning, about 50% of the lightning current that comes down on the lightning rod escapes to the ground, and the remaining 50% flows into the building through gas pipes, water pipes, communication lines, and power lines. (In case of integrated grounding or common grounding of common ground)
In the event of a lightning strike on a building, damage to facilities and systems occurs due to surges that are directly conducted through the power system.
Even if it is protected from surges directly conducted to the power system, an induced voltage is generated in the building's internal cable due to the lightning current flowing through the down conductor, causing damage to the facilities and systems connected to the cable.
In addition, even if a lightning strike does not fall on a building, if there are two buildings near the lightning strike point, there is a difference in the ground potential between the buildings according to the distance.
If the electrical system is housed inside each building and there is no system connected between the buildings, this potential difference does not cause any problem.
However, if the two buildings are connected by a LAN cable, the equipment in one building has a relatively high ground potential compared to the equipment in another building, which destroys the insulation of the LAN equipment and causes damage.