IEC 61958:2000 pdf download-High-voltage prefabricated switchgear and controlgear assemblies – Voltage presence indicating systems.
5.4 Coupling element and voltage limiting device 5.4.1 Insulation of coupling element The coupling element shall provide adequate insulation between its output terminal and the main circuit. 5.4.2 Voltage limiting device To provide protection for operators against the presence of operating voltage on the connecting point, it shall be ensured that any insulation failure of the coupling element will necessarily cause a permanent earth fault. This shall be achieved by connecting the coupling element output terminal to earth via a voltage limiting device. The voltage limiting device can be a specific component (for example, spark gap) or be one of the components permanently connected to the coupling element (for example, an indicating element component). The effects caused by the response of the voltage limiting device shall be taken into account when determining the protection concept of the installation. 5.4.3 Threshold voltage of voltage limiting device The threshold voltage of the voltage limiting device shall comply with the following requirements: – it shall be lower than 30 % of the nominal voltage of the power system; – it shall be less than the lowest limiting value of the dielectric strength in the remaining components of the VPIS.
5.4.4 Earth fault conditions For systems with insulated or resonant earthed neutral, earth fault currents are limited to low values and the equipment can be maintained in operation for a long period of time under these conditions. In such cases, additional precautions shall be taken to ensure that either the earth fault condition can easily be observed by operators, or no dangerous voltage can occur on the connecting point for the earth fault duration. 5.4.5 Maximum current delivered by the connecting point The current delivered by the connecting point when it is short-circuited to earth and with rated frequency and rated voltage between conductor and earth shall not exceed 2 mA. If the degree of protection of the connecting point is lower than IPXXB, the current value shall be limited to 0,5 mA. 5.5 Marking Marking shall be legible and permanent. It may be printed, engraved or moulded on the VPIS casing or switchgear front panel in the vicinity of the indicating element and connecting point.