A test signal is applied from a continuity test source to a photovoltaic (PV) panel string, to test electrical continuity in the PV panel string and between the PV panel string and an inverter that is coupled to the PV panel string. If the test signal is detected at a PV panel disconnect switch that is separate from the continuity test source and switchably couples one or more Direct Current (DC) PV panels in the PV panel string, then the PV panel disconnect switch is controlled to connect the one or more DC PV panels in the PV panel string. Otherwise, the PV panel disconnect switch is controlled to disconnect the one or more DC PV panels from the PV panel string. The test signal could be, for example, an Alternating Current (AC) signal tuned to a PV installation that includes the PV panel string and the inverter.

Safety device for an electrical apparatus powered by an AC mains power supply, the safety device comprising: an electric circuit having inputs for connecting to an active, neutral and earth conductors of the electrical apparatus which are in turn coupled to the AC mains power supply, the circuit being operable to: produce and apply a stepped down voltage and current to the earth conductor from the main supply; and electrically isolate the active and neutral conductors from the earth conductor in response to detecting that either: the active conductor is incorrectly wired to the neutral circuit of the AC mains power supply; the neutral conductor is incorrectly wired to the active circuit of the AC mains power supply; or the neutral conductor is switched; wherein one or more solid state relays are employed by the circuit for both producing the stepped down voltage and electrically isolating the conductors from earth.

A subsea electrical unit is provided. The subsea electrical unit includes a first electric power connection for receiving electric power for operating the subsea electrical unit and a second electric power connection towards a further subsea electrical unit. A line insulation monitor is coupled to the second electric power connection. A control unit is adapted to determine whether electric power is present on the second electric power connection, and is further adapted to disconnect the line insulation monitor form the second electric power connection if it determines that power is present on the second electric power connection.

A monitoring system is described, to monitor the condition of an industrial wiring system provided with a multipolar electric cable with a number of electric conductors having a power and/or data transmission function and enclosed inside a protective sheath, wherein: monitoring conductors, to monitor wear of the electric cable, are arranged inside the protective sheath electrically insulated from the electric conductors; and a monitoring device is operatively coupled to the monitoring conductors so as to detect at least one electric parameter associated with the monitoring conductors to detect the wear of the electric cable and generate corresponding monitoring data. The monitoring device obtains its own power supply from, and/or transmits the monitoring data by means of, the electric conductors of the same electric cable.

An apparatus for phase operation indication includes a phase filter that filters a ground monitor signal from one or more phase conductors supplying power to a load and injects the ground monitor signal in an equipment grounding conductor run with the one or more phase conductors or receives the ground monitor signal from a signal generator and injects the ground monitor signal on the one or more phase conductors. The ground monitor signal includes a test frequency different than a line frequency of power supplied to the load. The apparatus includes at least one indicator circuit connected to at least one of the one or more phase conductors. An indicator circuit of a phase conductor provides a visual flashing signal in response to a voltage being present on the phase conductor, the at least one indicator circuit located at the phase filter.

In a method for supplying an electrical load of a vehicle with electrical energy by auxiliary converters connected in parallel on the alternating-voltage side, a current flow between the auxiliary converters and a grounded N conductor of an energy supply network is interrupted in the presence a ground fault. The auxiliary converters connected in parallel on the alternating-voltage side are operated with fundamental-wave and pulse synchronicity. An energy supply system of a vehicle, in particular of a rail vehicle, performs this method, with the energy supply system including at least two auxiliary converters arranged in parallel, an energy supply network for supplying electrical loads, at least one switch for interrupting a current flow between the auxiliary converters and the energy supply network.

In a method for supplying an electrical load of a vehicle with electrical energy by auxiliary converters connected in parallel on the alternating-voltage side, a current flow between the auxiliary converters and a grounded N conductor of an energy supply network is interrupted in the presence a ground fault. The auxiliary converters connected in parallel on the alternating-voltage side are operated with fundamental-wave and pulse synchronicity. An energy supply system of a vehicle, in particular of a rail vehicle, performs this method, with the energy supply system including at least two auxiliary converters arranged in parallel, an energy supply network for supplying electrical loads, at least one switch for interrupting a current flow between the auxiliary converters and the energy supply network.

An apparatus including a test device for assessing the quality of a safety ground is provided. The test device is configured to receive an energy signal from a power source for charging a vehicle and to generate a first output signal in response to the first energy signal. The test device is further configured to measure a characteristic of the first output signal and to provide a test signal. The test device is further configured to generate a second output signal in response to providing the test signal and to measure a characteristic of the second output signal. The test device is further configured to assess the quality of a safety ground in at least one of the power source and the vehicle based on a difference between the characteristic of the first output signal and the characteristic of the second output signal.

A PE line protection system for a power utilization and charging apparatus, and a power utilization and charging apparatus, where the PE line protection system comprises a driving circuit (1) and a switch (2). The driving circuit (1) is used for controlling the switch (2) to cut off a PE line upon reception of a signal for indicating the abnormal connection of the PE line that is transmitted by the power utilization and charging apparatus. When the PE line is abnormally connected and a wrong current flows into the PE line, for example a live line or a live conductor is connected to the PE line, the switch (2) connected to the PE line can cut off the PE line in time, which can avoids the possibility of being electrified of a metal part of the apparatus and ensures the safety of the whole charging process.