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carried out, if possible, when the network is being designed using
calculations, and must be performed during commissioning using
measurements; this check is the only guarantee that the system
operates both on commissioning and during operation, as well as
after any kind of work on the network (modification, extension).
5. Passage of the protective conductor in the same trunkings as the
live conductors of the corresponding circuits.
6. High earth fault level under earth fault condition.
7. Low power factor (high inductance of long cable)
8. Requires extra equal potential bonding.
9. On occurrence of an insulation fault, the short-circuit current is
high and may cause damage to equipment or electromagnetic
disturbance.

(2c) TN-C-S System
• The Neutral and Earth wires are combined within the supply
cable.
• Typically this will be a concentric cable, with the live as the
central core, and a ring of wires around this for the combined
neutral and earth.
• At the property, the Neutral and Earth are separated, with the
earth terminal usually being on the side of the cutout. Inside the
cutout, the live and neutral are linked.
• Throughout the supply network, the combined earth/neutral
conductor is connected to the ground in multiple places, either
buried underground or at the poles for overhead supplies.
• This multiple earthing is why a TNCS supply is often called
PME (Protective Multiple Earthing).

Advantages
• Cost for core cable is cheaper than a 3 core.
• .As the outer sheath is usually plastic, there are no problems with
corrosion.
Disadvantages
• When the combined earth/neutral conductor is broken. This
results in a voltage appearing on the exposed metalwork in the
customer’s property, which can be a shock risk.
• This happens as the earth and neutral are connected in the cutout,
and there is no direct connection to the ground other than in the

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