Webinar «Lightning protection of accessible roof area», page 2

The sixteenth webinar of the series "Grounding and lightning protection: questions and answers arising at the design"

Webinar text. Page 2

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Ток короны, А – Corona current, A

Стержень - Rod

Радиус цилиндра- Cylinder radius

Цилиндр - Cylinder

Стержень - Rod

Время, с – Time, s

Сильное влияние радиуса кровли обусловлено большим удалением фронта объемного заряда короны от вершины стержня (30 м)- Strong impact of roof radius is conditioned by large remoteness of corona spatial charge front from the top of the rod (30m)

— It's not only the prerogative of such high-rise buildings. I made approximately the same calculations for a simpler case; I took a building 50 meters high. I got dependencies which tell practically the same. The less is the roof radius, the weaker is the effect of the lightning rod protective action, and a roof with a large diameter shields the top of the lightning rod and it starts to function not that well. Neither Russian, nor foreign document takes this fact into consideration. It means that everything that is done in this relation is only a convention.

At the construction of brick or  reinforced concrete – only the roof and equipment on it should be protected

Lightning protection mesh doesn’t perform this function

Rod or catenary wire lightning rods are required

Solution of the task with single or double lightning rods is not reasonable due to their great height; increase the frequency of direct lightning strikes, and, consequently, number of dangerous pickups.

Multi-electrode system is more preferable

— I think I've already showed you one picture. I made it on the roof of one warehouses of a lightning protection company in Germany. Covered climate-control machines are located in the centre of this thing. And rod lightning rods stand around the zone which should be protected from a direct lightning strike. These rods are 2,5 meters high and are located around the whole perimeter of the protected area. They will provide protection according to IEC standards, but if you try to do the same, Gostekhnadzor will tell you that you have no minor ground to make the same protection. Do you know how to struggle with Gostekhnadzor and to make rational lightning protection? In my opinion, the answer is yes.

При – at

Зона защиты не имеет провеса – Protection zone doesn’t have a sag

При расстановке с шагом L стержни будут эквивалентны замкнутому тросу – with the placement using the distance L, the rods will be equivalent to the closed wire

— I take a standard picture which can be found in all our lightning protection guidance. This standard picture shows me the protection zone of a double rod lightning rod. Here is one lightning rod, here is another, and this is the protection zone inside this rod lightning rod. This distance is a protection zone sag, it can be zero, and protection zone can be a vertical line in case if the distance between the lightning rods is 2,5 m high or less for a protection zone with a reliability of 0,9. Or if your distance between the rods is 2,22 of their height or less, if your protection zone reliability is 0,99. So in other words, if you put a 3-meter lightning rod on the roof and the distance between these lightning rods is 6 something meters or less; their protection zone turns into a straight horizontal line. Then this protection zone is equal to the wire protection zone and it means that you can substitute ground wires to lightning rods easily. If you put them with a distance which corresponds to these calculation formulas from any lightning protection guidance. So a ground wire can be substituted with a set of lightning rod and lightning protection won't suffer. But these distances should be observed. They are recorded in IS 153-34. You will find them for any protection reliability.

Standard: DIN EN 50164-1

1. Preparation of a sample

Preliminary installation of the sample

Tightening of bolts with a torque recommended by the manufacturer (usually 25 H*m)

Measuring of the transient resistance of the contact connection

<= 0,001 Ohm (galvanized steel, aluminium and copper) or <0,0025 mOhm (stainless steel)

AD 34.21.122-87

3.4. Connections of lightning rods with down conductors and down conductors with ground electrodes should be performed by welding, as a rule. And if flame works are not allowed, bolt connections with a transient resistance not more than 0,05 Ohm can be performed with an annual control of the latter before the thunder season

— Why we can do it this way? Look at the bolt connections shown on this poster; they are tested in the following way. They are tightened with the force of 25 N*m, then the transient resistance together with the bolt clamp connection of lightning protection elements should be not higher, than 1 mOhm, if it is non-ferrous metal and 2,5 mOhm if it is stainless steel.

Useful materials for designers:

• Webinars with the leading industry experts
• Everything for the calculation of grounding and lightning protection
• Useful materials: articles, recommendations, examples

Webinar «How to choose lightning rods after all?», page 1 6. How to do that? Webinar «Fire Safety and Regulatory Requirements to Lightning Protection», page 1 Webinar «Fire Safety and Regulatory Requirements to Lightning Protection», Page 2 Webinar «Fire Safety and Regulatory Requirements to Lightning Protection». Page 3