Cable Screen and Concentric Earth Conductor in Medium-Voltage Cables

A conductive layer (usually of copper wires or tape) applied around the insulated core(s) of a medium-voltage cable, serving two functions at once: confining the electric field around the insulation to a defined, safe value at the outer surface of the cable, and acting as the return path for earth-fault currents during a single-phase earth fault in the network. When correctly sized per NEN-EN 60502, this screen must be able to carry the full expected earth-fault current for the protection's disconnection time without unacceptable temperature rise, and the screen must be earthed correctly at both cable ends — single-ended or double-ended, depending on the design — to avoid unwanted circulating currents or, conversely, an interrupted return path. A damaged or incorrectly earthed cable screen is a common, hard-to-detect cause of elevated touch voltage during an earth fault in medium-voltage networks.