| 摘要 |
A safety method and safety apparatus of an electric installation (2) that is powered through an electric supply line (3), and has a ground wire (9). The safety apparatus comprises a means (400A) for automatically measuring (71) the voltage (&Dgr;V) that is established between the neutral point (1,23) of the transformer (26) of an electric supplying network and the ground wire (9). A comparison (74) is then made between the measured voltage (&Dgr;V) and an alarm voltage value (&Dgr;V). Finally, a switch (33) is activated (79) by means of a control device (370), when the measured voltage (&Dgr;V) exceeds an alarm voltage value (&Dgr;V), and the electric supply line (3) is automatically disconnected from the electric installation (2). The invention is adapted to prevent, in particular, dangerous contact voltages from building up on the a ground terminal that is shared by all the electric installations of a living unit of multifloor building that would be transferred to all the electric installations that are connected to ground. In an voltamperometric exemplary embodiment, a selective opening is possible of the switches pertaining the living unit that have caused the dangerous voltage to build up, for example in case of failure of a residual current circuit breaker device. The system may also provide giving a pre-alarm, for voltage values that are close to the dangerous voltage value, or turning off the electric supply to the circuits of each living unit (according to a possible preference) that produce a ground current greater than a design value. The system may also provide steadily detecting a ground resistance.
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