The first part of the article "Lightning protection at a construction site"
An old Russian proverb says, that one should bring his child up when he/she is lying across the bench, not along. The situation with lightning protection is similar on the whole. The regulaton of the Instruction on lightning protection AD 34.21.122-87 start to worry when the walls of the building under construction will raise to 20 m. It is quite a careless regulation. You need to begin at once, as soon as the place for the foundation is defined. The first but crucial question - what soil is there at the construction site?
It is not that easy to get the right answer. Lightning current goes very deep into the ground. Computer researches showed that the equivalent depth of lightning current penetration is compatible with the maximal size of the grounding device, which will be used in lightning protection. It means, we are talking about the foundation of the future building. Its maximal size - foundation diagonal. It means, at a serious construction site, the ground should be researched for the depth of about 100 m. The method for that is already well-known. Almost all manuals recommend vertical electric sounding - this operation is not easy at all, and is not very accurate. But, no special accuracy is needed, if we are talking about the preliminary estimation of ground resistance.
There is a possibility to simplify ground state analysis. If to proceed from everything said above, the depth of the ground layer, where the current is being spread, is defined by the maximal size of the grounding device. It weakly depends on its shape. The simplest ground electrode system is the horizontal bus. It is possible to dig a horizontal trench 0,5 m deep without any great expenditures. Its length should be equal to the diagonal of the future foundation. It only remains to put a horizontal metal bus into it and bury and ram it thoroughly in order to recover the structural surface of the ground. Grounding bus resistance measuring doesn't cause a problem. Its calculated value is connected with the equivalent resistivity of the ground by a well-known formula
E. M. Bazelyan, DEA, professor
Energy Institute named after G.M. Krzyzanowski, Moscow
Read more "2. Measuring ground resistance of the foundaton"
- Lightning protection of residential and public buildings (article by professor E.M. Bazelyan)
- Free webinars for designers of grounding and lightning protection
- Soil resistivity chart
- Solutions on grounding and lightning protection projects in dwg, pdf formats
- Free consultations and assistance in calculation of grounding and lightning protection