A TN-C-S system, has the supply neutral conductor of a distribution main connected with earth at source and at intervals along its run.
This is usually referred to as protective multiple earthing (PME). With this arrangement the
distributor’s neutral conductor is also used to return earth fault currents arising in the consumer’s
installation safely to the source. To achieve this, the distributor will provide a consumer’s earthing
terminal which is linked to the incoming neutral conductor.
- IEE Wiring Matters