The smallest distance between the part of grounding communication device, which is not connected into its own transformer station should be at least 20m from the grounding power equipment part up to 1000V and 40m far from the grounding power equipment part over 1000V. If there is no way how to abide at least half of the mentioned distances, there is urgency to make one of the following arrangements:
a) It is necessary to make sure by calculating or measuring, that voltage on a communication equipment induced by the highest currents in grounding of power equipment doesn´t exceed permissible limit.
b) Both groundings are connected through, if it doesn´t evoke undesirable consequences of direct coupling (for example importation of dangerous or disturbing voltage into communication system, creation of route for stray currents or creation of macrocell with electrodes created by particular groundings).
The grounding of conductors and power equipment doesn´t have to be connected together, if the distance between two groundings in foundation soil is bigger than 5m. The grounding of the communication equipment should be as far from grounding of conductors as possible. If the distance between grounding of conductors and any other part of grounding of communication equipment is smaller than 5m, the both groundings must be connected through. Then joint earth termination system must agree with the standard EN 62 305 and with the rule set for communication equipment. Operating grounding of the overvoltage conductors is connected to protective grounding equipment, which are protected by surge arrester. In the chapter Grounding and protective conductors there is mentioned that generally protective conductor PE can be bare and must be laid together with outlying conductors. Grounding conductor, which goes to subsidiary grounding conductor, must be isolated so as it´s prevented from contact with protective conductor or any part connected to it or with dead parts, which are connected to the protective conductor. It is necessary to fulfill this condition so as by-pass of detectors is avoided. Protective conductor can be connected only to dead parts of those electrical subjects and equipment, whose power supply is disconnected in case of voltage protector equipage failing.
The dead parts must be connected to a protective conductor during compliance of given conditions for every recommended kind of power system grounding. The dead parts, which are touchaccessible at the same time, must be connected to the same earth termination system separately, in groups or together. These conductible parts must be connected together into so-called main protection connection in every building: protection conductor, grounding bonding bar or main protection clamp, conduit distribution in a building, for example water and gas, metal constructions and central heating and air-conditioning (if they are in the building). The conductible parts, which come into the building from outside must be connected as close to their entrance into the building as possible. Of course the conductors of main connection must comply with their crosssections. The main connection must be done at every metal coating of communication cables. However it is necessary to obtain an approval of these cables owner or operator.