Lightening is one of the main sources of damages for the Parishes. Generally, the bell tower is a building having the right shape and height to be the privileged destination of lightening fall.
Lightening can also be indirect and enter into the electrical plant of the church coming from electricity grid as overvoltage created outside; that happens because of the lightening falling nearby the church, lightening able to strike directly the electricity grid inside the building or fall to the ground and from there go back up to the church electrical plant.
Lightening able to strike directly the electricity grid inside the building or fall to the ground and from there go back up to the church electrical plant
Before starting a project on a lightening conductor, a report about main risks caused by lightening is prepared:
- risk of human deaths or injuries
- risk of structure damages
- risk of electrical or electronical equipment damages.
The risk depends on many factors like dimensions and geometrical shapes of the building, its position, the area where it is located, its use classification, etc..
After taking correctly account of the risks, the report ends with the lightening conductor project that lists the necessary operations to keep the risk level within the limits fixed by regulations.
A complete protection system must consider two kinds of protections:
- LPS: direct atmospheric discharge protection system
- SPD: overvoltage protection devices
A LPS consists of:
- A series of sensors aiming to intercept and attract lightening directed to the building. The sensor system consists of air-termination rods, air-termination tips and metal conductors placed on the building to form an air-termination mesh having the correct geometry.
- A down-conductor system linked to the air-termination system, realised through metal conductors, properly placed along the building walls, that allow the lightening discharge electricity to reach the ground through parallel paths.
- An electrodes system or ground termination system: consisting in a conductors mesh, placed into the ground, to cover the area as widely as possible, aiming to scatter the lightening discharging in the ground without any risk. To achieve the best result it is necessary that the electrode offers the lowest impedence (or ground electrode resistance), because the lower that value is, the higher the percentage of the discharging current scattering on the ground, without causing damages, will be. .
The SPD or discharger has the function to protect the building and the electrical plants inside of it against the electrcity grid overvoltages that may occur during direct or indirect lightening or also because of incorrect operations on the power electricity grid, outside the building too.
Depending on their position in the electricity grid, the SPD are classified in the following way:
- SPD type 1: they are connected to the electrical switchboard from which electricity grid is generated (electricity meter) and their function is to withstand direct lightening discharges. They need a connection to the ground discharger to which they divert the discharge current.
- SPD type 2: they are connected to the electrical junction box containing disconnecting swtiches of the various building plants. They withstand indirect lightenings discharges and they need connection to the ground electrode too.
- SPD type 3: they protect one single item of equipment against lower current discharges, not strong enough to make the SPD type 1 and 2 start to work, able to damage rather delicate equipment, usually electrical devices.