IP networks are actively used by public services and now provide information transfer which includes different services, such as IP telephony, video conference, data exchange and others. Such services are most sensitive to delays and errors, at reproduction on the receiving device, in comparison with telephone conversations. Therefore, there is a need for a research of the different factors which are negatively affecting quality and timeliness of communication. One of the main factors are external influences on an electric cable of communication which will be considered most in detail. External influences (noises) in data transmission lines can lead to errors in signal equipment on a receiving end or even to breakdowns of the equipment. All know about risk, which is connected with jumps of power supply, but at the same time underestimate effects of such processes in data transmission lines. Especially in a century of information technologies when divisions of special communication pass to new, more advanced equipment and along with it less maintainable, in case of faults, this subject becomes the most relevant.