Surge Arrester or the lightning strike risk protection  
Parafoudre
Energy surge arrester
1 Direct strike –on the building
2 Indirect strike –on an aerial electric line
3 Indirect strike –through the earthing network
Protection Telecom

Telecom surge arrester
The risk linked to overvoltage
The effects of lightning can be the consequence either of a direct stroke on the power line, or an induced lightning stroke close to the line producing in its surrounding electrical fields that generate hazardous overvoltage.
The direct consequences are :
- destruction of electrical and electronic networks and equipment
- loss of data
- loss of communication
- production shutdowns
- paralysis of logistics
- safety failures
A lightning impact induces voltage surges that are carried by any type of conductor (main power, telephone, TV, computer cables, buses, etc). The multiple networks, their interconnections and the growing use of sensitive electronic devices in our everyday life are as many factors of increased lightning risk. The consequences of lightning can be perceived within a radius of 10 km around the ground impact.
Lightning arrester selection and coordination  
Lightning arresters are selected mainly according to :
- their maximum discharge current
it represents the maximum absorption capacity of the lightning arrester on transient phenomena
- their protection level
it represents the residual voltage applied to the protected equipment

  
When a low protection level and a high rated current are required, it is sometimes impossible to find a solution with only one lightning arrester. In this case, it is necessary to install several coordinated lightning arresters.

A lightning arrester having the required maximum current is placed at the head of the installation, and another lightning arrester having a protection level compatible with the equipment withstand voltage is placed as close as possible of the equipment protected.
Risk calculation

The probability of undesired effects caused by lightning is related to several parameters :
- site exposure
- technical characteristics of installation
- presence of a lightning conductor
- equipment sensitivity
- economic consequence of the damage
- cost of unavailability