Necessity of Short-Circuit Making Capability for Earthing Switches in MV RMUs
2026-01-05 Functional Role of the Earthing Switch In medium-voltage ring main units (RMUs), the earthing switch (ES) is often regarded as a device intended solely for maintenance grounding. However, under several credible operating and fault conditions, the earthing switch may be required to make onto a live circuit and withstand the resulting short-circuit current. For this reason, IEC standards explicitly require earthing switches to be designed and tested for short-circuit making capability, rather than treating this as an optional feature. Typical Operating Scenarios Requiring Short-Circuit Making Capability 2.1 Inadvertent Closing onto an Energized Circuit In the event of mis-operation or interlocking failure, an earthing switch may be closed onto an energized […]
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