Changes to AREI TN-C Power Systems: Where Does the Risk Lie?

There have been changes to the regulations governing the installation of TN-C power systems.

The TN-C power system is prohibited:

When the grounded active conductor (PEN, PEM, and PEL) is used in a final circuit;
In residential installations, common areas of a residential complex, and electrical installations without BA4/BA5-certified personnel;
In areas characterized by external influences BE2 and/or BE3 and/or CA2;
For the designated current path of an electric vehicle charging station;
In temporary, mobile, or relocatable electrical installations.

In addition, the grounded active conductor (PEN, PEM, and PEL) must have a cross-sectional area of at least 10 mm² for copper or 16 mm² for aluminum, unless the nominal voltage of the current path is limited to the conventional absolute voltage limit UL

No exception is made for 2-phase circuits. A transitional provision applies to this last requirement for projects or work whose on-site execution began before April 1, 2026.

Schematic representation of a fault current within a TN-C power system in an electrical installation.

Schematic representation of an earth connection and fault current within an electrical grid.

Changes to AREI IT Network Systems: Monitoring Becomes a Responsibility

In addition to the existing options for active protection against electric shock in the event of indirect contact, two new options are being added. This brings the total to six possible devices or equipment that may be used, namely:

Overcurrent protection devices
Residual current protective devices
Overvoltage protection devices
Devices for continuous insulation monitoring that can be combined with an insulation fault detection system
Residual current insulation monitoring devices (*) (new)
Monitoring devices using technology that ensures at least an equivalent level of protection as one of the two preceding devices (**) (new)

(*) Residual current insulation monitoring devices are devices that either trip the circuit or sound an alarm when a leakage current is detected. Residual current protection devices, on the other hand, will always trip when a residual current is detected.

(**) This option was added to allow for future flexibility in case other types of isolation monitoring devices become available on the market.

When an IT power system does not automatically interrupt the power supply upon the first fault, a new regulation now applies. Continuous monitoring is required to detect the occurrence of an initial ground fault, and one of the last three devices listed above must be used for this purpose.

A transitional provision applies to this last regulation for projects or work whose on-site execution began before April 1, 2026.

Schematic representation of an IT power system with fault current and ground connection in an electrical installation.

Schematic representation of an IT system with isolation monitoring for electrical installations.

Residual Current Protection in Non-Residential Installations: No Longer a Standard Table

Table 4.4 is being removed from Book 1. The maximum permissible sensitivity of the residual-current device must now always be calculated using the formula:

IΔn × RE ≤ UL

where:

IΔn in A: sensitivity of the residual current device;
RE in Ω: earth resistance of the ground connection between the masses
UL in V: conventional absolute voltage limit

The earth connection resistance must never exceed 500 Ω for dry and non-conductive spaces (AD1, BB1, and BC1) and 250 Ω for other spaces (AD2 through AD5, BC2, and BB2).

A table of technical values for trip currents and resistive components in protection systems.

What happens if this is not evaluated?

During a subsequent inspection, this could lead to:

✔ Observations or violations

✔ Mandatory corrections

✔ Internal discussion regarding responsibility

✔ And in the event of an incident? Then it will be determined whether you could reasonably have known that the regulations had changed.

Do you want to ensure your installation remains compliant with the changes in 2026?

Normec BTV helps you:

✔ Technically assess your current situation
✔ Clearly identify risks
✔ Demonstrate compliance

No unnecessary interventions. Just clarity.

Contact our experts at com-btv@normecgroup.com.

Looking for an independent inspection partner?

Normec offers expert and independent inspections to ensure the safety of buildings, installations, and facilities.

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