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Studies conducted in the US show that the strength (in imp) of:
98% of all lightning is under 60 kA
95% of all lightning is under 30 kA
45% of all lightning is under 10 kA
According to IEC standards, the maximum in imp that can occur is 200 kA. Of these 200 kA, 100 kA is assumed to disappear into the ground and 100 kA reaches the installation. These 100 kA are then distributed to each part in the cable, which means that in a 4-cable system, no more than 33.33 kA can reach the object to be protected and in a 5-cable system, no more than 25 kA can reach the object.
What should be protected? Single-family homes in densely populated areas, industrial premises, farms, apartment buildings, office complexes…? Generally speaking, one stage of protection is enough for a single-family home, but two or more stages are preferable in other situations.
The following advice should be viewed as suggestions and can be adapted or supplemented to suit the relevant circumstances. If you are unsure of how to proceed, please contact us for help.
Single-family homes in densely populated areas: Intermediate protection (type 2). The best location is in the meter cabinet, if there is room and if the cabinet has been prepared for it. Otherwise, the surge protector can be mounted directly after the switch in a standard distribution board, or directly beside it in a separate standard enclosure in the case of Diazed (D-type) distribution boards. If there is an underlying distribution board in another building that contains sensitive equipment, this should also be protected, in this case with type 3 surge protection.
Single-family homes in rural areas: Combination protection or reinforced type 2 protection. These protectors have the combined properties of both type 1 and type 3 protectors.
Industry: Combined protection or reinforced type 2 and then type 2 in distribution boards and type 3 in control cabinets.
Farms and agricultural holdings: Type 1 in meter cabinet, Type 2 in underlying distribution boards and Type 3 at sensitive equipment, e.g. computer-controlled feeders.
Apartment buildings: Combined protection at main electrical switchboard and Type 2 at underlying distribution boards.
Office complexes: Combined protection at main electrical switchboard and Type 2 at underlying distribution boards, with additional Type 3 at each underlying distribution board.
Note: Proximity to tall buildings, churches and similar always increases the risk of being exposed to surges and means that several stages of protection should be installed. If a building has a lighting rod, the first protector must always be Type 1. Surge protectors must always be installed before any earth fault breakers.
Last but not least, keep in mind that even if you choose the wrong protection for the application, you will always have protection that "does its job” though perhaps not as quickly as can be expected.