Earthing of TelephoDe EschaDge Office PART ONE: Measurement of earth resistivity by finding the voltage distribution on its surface

Nowadays for many purposes an earthing system in telephone exchange
office will be designed such as, transmission, protection and lessen the amount of crosstalk, so that is the reason why these kind of matters have put in an appearance seriously.
For example in the case of prositive pole of battery crosstalk will be
reduced. In telecommunication lines some of the speech currents may go from one line to the others through earth and as a result cause crosstalk. But if one of the poles of exchange battery is earthed, the path of leakage currents will be returned to the line and consequently reducing crosstalk.
The amount of earth resistance estimated to be below O. 5 n for the large
offices having a capacity about 10,000 subscribers and more.
It is common to say that acquiring this value is rather difficult referring
to the different kinds of soil.
In that case, a lot of countries prefere to design a system with a high
amount of resistance from the view point of economy. According to C. C. I. T. T. recommendations, measurements are shown that the lead sheath of cable are able to reduce it by 60- 90 per cent. But referring to the decision of cable factories, which are going to change lead sheath to PE, they will automatically be canceled.
For this reason designing a group electrodes will be very important.
There are many factors effecting upon earthing resistance, which among
them soil resistivity plays the main role.
To the best of the author's knowledge, the soil properties are very changeable
and not really under control.
To tell the truth estimation of future value IS the main difficulty upon
our designing.
In this article we've shown different methods for measuring earth resistivity and acquaintance with stratification of earth layers to find a suitable
method for selection of electrodes.