I am thinking like an English electrician, not an Irish electrician so it’s good job I am not taking an Irish Regs exam.


This needs considering in the context that all TNCS-PME earthed installations have to have their own earth rod which is effectively connected to the DNO supply cable PEN neutral.

Analytical Testing Ireland


Pages 12 and 13.


TN-C-S System

The 230 Volt single phase supply to a premises is taken from the secondary winding of a DSO transformer. One terminal of this secondary winding is connected to earth ( ground ). This terminal becomes the neutral for the system. The neutral conductor is therefore at earth potential ( zero volts ).

A two core concentric cable is generally used to connect from the supply network to the premises. The centre core is the phase conductor. The outer core performs the functions of neutral and protective conductors. This conductor is known as a PEN conductor. It is terminated at the DSO main fuse unit.

PEN = PE for protective conductor ( protective earth ), N for neutral conductor.

From this point on, the neutral and protective conductors are separated and must not be connected together, anywhere throughout the entire installation. The protective conductor is referred as the Main Protective Conductor. It is connected to the Main Earthing Terminal of the installation. This means that the Main Earthing Terminal is solidly connected to the DSO neutral.

At each installation an earth electrode is provided. The earth electrode is connected to the Main Earthing Terminal and therefore to the DSO neutral. This arrangement provides the consumer with an earth terminal, which is connected to the neutral conductor of the system, thereby providing a low impedance ( low resistance ) path for the return of earth fault currents.

Impedance is the ratio of AC voltage and current. The Ohm is the unit of impedance. Its symbol is the letter Z.

I am thinking like an English electrician, not an Irish electrician so it’s good job I am not taking an Irish Regs exam.


This needs considering in the context that all TNCS-PME earthed installations have to have their own earth rod which is effectively connected to the DNO supply cable PEN neutral.

Analytical Testing Ireland


Pages 12 and 13.


TN-C-S System

The 230 Volt single phase supply to a premises is taken from the secondary winding of a DSO transformer. One terminal of this secondary winding is connected to earth ( ground ). This terminal becomes the neutral for the system. The neutral conductor is therefore at earth potential ( zero volts ).

A two core concentric cable is generally used to connect from the supply network to the premises. The centre core is the phase conductor. The outer core performs the functions of neutral and protective conductors. This conductor is known as a PEN conductor. It is terminated at the DSO main fuse unit.

PEN = PE for protective conductor ( protective earth ), N for neutral conductor.

From this point on, the neutral and protective conductors are separated and must not be connected together, anywhere throughout the entire installation. The protective conductor is referred as the Main Protective Conductor. It is connected to the Main Earthing Terminal of the installation. This means that the Main Earthing Terminal is solidly connected to the DSO neutral.

At each installation an earth electrode is provided. The earth electrode is connected to the Main Earthing Terminal and therefore to the DSO neutral. This arrangement provides the consumer with an earth terminal, which is connected to the neutral conductor of the system, thereby providing a low impedance ( low resistance ) path for the return of earth fault currents.

Impedance is the ratio of AC voltage and current. The Ohm is the unit of impedance. Its symbol is the letter Z.