Revised TAR Low Voltage responds to rising connected loads in buildings and establishes more uniform guidelines for planning, metering and installation

As the electrification of buildings increases, so too do the demands placed on their electrical infrastructure. Photovoltaic systems, heat pumps and charging points increase the required connection capacities and present planners and specialist electrical contractors with new challenges. The VDE-AR-N 4100:2026-04 ‘Connection and Operation of Customer Installations on the Low-Voltage Network (TAR Low Voltage)’, which has been in force since 1 April 2026, takes this development into account. This is highlighted by the German Society for Economic Cooperation (DGWZ).

The amended application rule defines the minimum technical requirements for the design, installation, connection and operation of customer installations on the low-voltage network. A key change concerns metering systems and, in particular, transformer systems: the latter are explicitly included in VDE-AR-N 4100 for the first time and are thus subject to greater standardisation.

Transformer systems are gaining in importance in the building sector

This move follows a trend that has long since ceased to be confined to commercial and industrial properties. With higher electrical power levels in buildings, traditional direct metering is increasingly reaching its limits. Alongside photovoltaic systems and heat pumps, wall boxes and higher-capacity charging infrastructure in particular are contributing to the likelihood that transformer systems may also become more frequently required in residential construction in future.

In current transformer measurement, the high operating current does not flow directly through the electricity meter. Instead, current transformers provide a signal suitable for measurement. For planners and installation companies, this raises the increasingly important question of when direct measurement is still sufficient and when a current transformer system must be taken into account as early as the planning phase.

The new VDE-AR-N 4100 is intended to create more uniform framework conditions for this. Until now, complete cabinets and transformer panels often had to be adapted to the differing technical specifications of the respective distribution system operators. The amendment now harmonises, amongst other things, the design and functional areas, as well as the requirements for transformer test terminals and voltage paths.

This is intended to reduce the effort involved in planning, product selection and installation. At the same time, more standardised technical specifications can help to reduce interface problems and sources of error during implementation.

New requirements for meter locations

The revised version also contains relevant changes for metering systems. For both BKE-I meter locations and 3-point meter locations, a distribution panel may optionally be provided above the system-side connection compartment (AAR) in future. This can be used, for example, to house control and protection devices for charging points.

For 3-point meter locations, a main switch in the AAR is also now mandatory. This allows the system to be disconnected from the grid on all poles. The regulation enhances safety at the meter location whilst also taking into account the growing technical complexity of modern building installations.

The changes demonstrate that the meter point is having to take on an increasing number of tasks. In addition to the actual metering, it must now fulfil requirements relating to grid connection, control and protection, as well as the integration of new electrical loads and generation systems.

Greater planning certainty for higher connection capacities

For electrical designers, the standardised specifications are set to bring particular benefits when dealing with more complex metering concepts. Requirements for transformer installations can be incorporated into building and electrical planning at an earlier stage, and technical coordination with network operators can be better prepared.

“For electrical designers, this makes the early-stage sizing of customer installations much more manageable: They gain clearer guidance when designing more complex metering concepts and can better take grid operators’ requirements into account as early as the design phase. This facilitates technical coordination and supports the safe implementation of higher-power applications within the building,” explains Ipek Rasitoglou, Communications Specialist at Hager Vertriebsgesellschaft mbH & Co. KG.

This early-stage sizing is crucial, particularly in view of ongoing electrification. If charging infrastructure, heat pumps, photovoltaics and other power-intensive applications are taken into account right from the planning stage, metering and connection concepts can be designed accordingly, thereby reducing the need for subsequent adjustments to the electrical infrastructure.

Technical regulations keep pace with electrification

The VDE-AR-N 4100:2026-04 adapts the technical connection rules for the low-voltage grid to an energy landscape in which buildings are increasingly generating, storing and consuming electricity simultaneously. The explicit inclusion of power conversion systems is more than just a minor change: it takes account of the fact that higher connection capacities and more complex energy flows are increasingly becoming part of everyday electrical planning.

Standardisation thus creates a common technical basis for network operators, specialist electrical contractors, planners and manufacturers. Particularly in the case of meter and transformer systems, it is intended to simplify planning and installation whilst ensuring the safety and technical compatibility of the systems.

In practice, the amendment means one thing above all: the design of the metering and connection infrastructure must, in future, be incorporated into building planning at an even earlier stage. This is because, with the growing number of electrical generators and consumers, it is not only connection capacities that are rising – but also the requirements for a safe, standardised and sustainable electrical infrastructure.