Protection of objects

This is an occasion to explain all of fundamental elements of lightning-rod installations and their functions for protection of buildings and other objects against lightning strike.
The first element is appliance for holding. It is the most emphasised part of lightning-rod and it's function is to pull closer and take over the lightning strike and in that way to protect objects below it. It appears in two primary shapes: like a rod or like a rope.
The second function of lightning-rod installation is to bring away the taken current of lightning from appliance for holding to earth with certainty. In this purpose, here we are putting one or more drains. They must resist the warming up caused by current of lightning passing through them.
The third function is to bring away the taken current of lightning as good as possible to the earth. In this purpose are subservient grounded conductor, which are dug in earth and connected to drain. Their resistance should be as small as possible so that drop of voltage could be smaller. That drop of voltage appears on the drain of lightning-rod and if it isn't small enough there could appear skipping across drains toward the other objects. It is especially relate to objects that are grounded on other way (for example, plumbing or gas-installations).

For these reasons there is tendency to make the grounded resistance and the drop of voltage smaller. In the same time, the measure named equalisation of potential is executed. It means that the grounded conductor should be connected with other metal parts from surrounding.

That way the skipping across drains toward the other objects can be barred.
Important part of lightning-rod installation is grounded conductor. It must conduct the current of lightning to the earth well, that is, it's resistance should be small as possible. That resistance is depending on earth feature and shape of grounded conductor. The earth feature important for construction of good-grounded conductor is "specific resistance of soil". It is defined as an electrical resistance of one cube (size 1m3) of homogeneous soil. If the specific resistance is bigger then dimensions of grounded conductor should also be bigger. The references of specific resistance of soil are visible in this table:

 type of material specific resistance [Ohm*m] sea water 0.5 water of rivers and lakes 10-100 swamp ground 90-150 plowed ground 90-150 humid small-grained sand 90-150 humid big-grained sand 200-400 dry small-grained sand 500 dry big-grained sand 1000-2000 rocky ground 100-3000 limestone 500-1000 concrete 150-500

The most usable constructions of grounded conductor are:
-lace - formed like metal lace which is covered with earth. Most often, the lace is mode of galvanised steel and less often it is made of copper.
-stick - formed like metal stick or tube which is covered with earth vertically
-fundamental - metal conductors which are installed in foundations of object and over the large area of concrete they are in contact with surrounding soil.

While current is passing through the grounded conductor and its wide-spread through the earth, there is distribution of potential.
Most often, it is in form of potential funnel. It means that the potential is the largest near the grounded conductor and with increase of distance from grounded conductor its value is falling off. It is logic because current makes the largest drop of voltage while it spread on a small area near grounded conductor. Farther away from the grounded conductor, current has larger area and smaller resistance so the drops of voltage are smaller.