Lightning rods on the roof (lightning protection of the roof)

Only Karlsson, who lives on the roof, doesn't suffer from lightning. For the rest, it is really dangerous on the roof in a thunderstorm. Everything that elevates above the roof contracts lightning. As a result, the number of strikes into the roof increases significantly. Oh please don't believe the talkative communication men. They will try to calm you down saying that antenna will perform the role of a natural lightning rod. It's of course so. Lightning current in antenna will anyway excite electromagnetic pickup. It is absolutely unsafe for electronic filling for a residential or office building.

The roof of a modern building is viewed as a useful space in which it is possible to install climat-control or ventillation machines, place multiple antenna systems and make spacial recreation zones with amusement rides and hanging gardens. All this requires lightning protection, especially for high-rise buildings.

E. M. Bazelyan, D. Eng. S, Professor;
G. M. Krzyzanowski Power Engineering Institute, Moscow;
acknowledged Russian expert in grounding and lightning protection

1. Norming of lightning rods on the roof

There arises the question about the place of installing lightning rods. It is clear, that you cannot place them on the ground at high-rise buildings, the expenditures are too high, and the architecture of the building won't look better with them. The only place for lightning rods is roof and it brings to the unsolved problems here. Take a look at fig. 1. It is taken from the lightning protection standard IEC 62305.

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2. Counter charge from a lightning rod on a roof

It is clear, that the roof won't influence the electric field at the top of the lightning rod, if its dimensional size is compatible with the radius of the rod electrode. In this extreme case, the protective effect of a rod lightning rod on a small roof should be equivalent to the lightning rod of the summary height (height of the building + lightning rod), mounted on the ground. In another extreme situation, it is necessary to study rod lightning rod, located far from the edge of a very large roof, the size of which exceeds the height of the rod. Now a lightning rod mounted on the ground must have an equivalent protective effect, but this time the height of the roof won't matter. We should only care about the height of the rod itself.

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3. About lightning protection mesh again

Ascertaining of imperfection of lightning protection theory won't make the life of the designers easier. They need to protect constructions on the roof today. The builders don't have time to wait until the scientific theory is developed. The national regulatory documents do not suppose anything good in fact. Lightning protection mesh is considered to be a panacea from all the diseases. It is put on the roof of almost all buildings, on those with reinforced concrete slabs as well. It is impossible to understand where this practice came from. In any case, it is not reasonable to blame the regulatory documents.

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4. Multi-electrode lightning protection system

It is not a surprise, but we will talk not about overhead power transmission lines, but about extended underground utility systems. It can be, for example, metal conduits or simply very long grounding buses. The running inductance of such utility system is approximately the same as of the overhead power transmission line. The capacity per unit length doesn't increase significantly (relative dielectric permeability of soil ε, as a rule is not greater than 10) and that is why, the condensance leakage current in many situations is much less than the current in the grounding devices.

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5. Features of lightning protection installation

The time interval for the calculation is chosen the way to provide the drawing of the lightning current pulse front. For example, at the front time of 10 ms (pulse 10/350 ms, on which SPD of the I protection level are chosen), gives quite a satisfactory result with the interval of 1 ms, at which the front is being drawn by 10 calculation points; at an interval of 0,1 ms (100 calculated points on the front) the result of the calculation appears to be brilliant. The question about the current pulses of the next components appears immediately.

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