Multiple grounding of 48 V DC power supply units endangers devices and causes the loss of availability

Inhalt:
In 48 V DC power supply systems of telecommunication systems the positive common conductor is directly grounded. Commonly the point of grounding is nearby the power supply. In existing systems it is not to be sorted out that there are further ground connections to be seen. Beginning with start of operation of a telecommunication system no one will recognize those possible multiple connections between the positive common conductor and ground. In practical life multiple grounding of the positive common ground conductor will be ignored as a cause of malfunction. The systems seem to run in the intended modes. Following Kirchhoff’s rule of current nodes such multiple grounding connections lead to ground currents passing through the DC power supply system. Those influences cause hardware damages and lead to loss of availability. The presentation describes the phenomenon and shows simple methods to sort out such failures in practice. It claims to apply an isolation measurement procedure to each of the system devices at the end of their manufacturing processes as well as an overall isolation measurement procedure of the DC power supply system at the end of installation of the complete telecommunication system. In this way ground faults will be detected before system operation starts. To increase the availability of telecommunication systems furthermore an additional permanent current monitoring system has to be brought in into the connection wire between the positive common conductor and ground. That current monitoring system detects isolation failures during normal operation as well as in cases of non-operation. Several alarm levels set different escalation levels for maintenance. The installation of such a permanent current monitoring system could also be done under running operating conditions without reduction of system functions. In case of degradation of the isolation quality of the DC power supply system the need for preventive maintenance will be offered in time. Failures could be sorted out before system breakdown happens. Sorting out multiple groundings of the positive common conductor and permanent monitoring of the current through the connection wire between positive common and ground afterwards reduce damages of devices and increase the availability of the complete telecommunication system to be protected.