VDE-AR-N 4110: medium-voltage connection rules explained

VDE-AR-N 4110 is the German technical connection rule for customer installations on the medium-voltage network, the TAR Mittelspannung. It sets the requirements for planning, building, operating and changing generation plants, storage, consumers and mixed installations connected above 1 kV and below 60 kV, and it implements the European network codes for generators (NC RfG, types B and C) and for demand connections (NC DCC) in Germany. The current edition is VDE-AR-N 4110:2023-09, applied from 1 September 2023.

VDE-AR-N 4110 at a glance

Sources: VDE FNN TAR Mittelspannung page and FAQ, the VDE Verlag product page and the VDE FNN list of application rules. The full rule is sold by VDE Verlag.

Which edition of VDE-AR-N 4110 is current?

VDE FNN lists VDE-AR-N 4110:2023-09 as valid. Its only technical change from the 2018-11 edition was the new individual verification route for plants from 135 kW to 950 kW. The requirements on generating units and components did not change, which is why 2018 unit and component certificates remain valid.

A full revision is under way. VDE FNN published E VDE-AR-N 4110:2024-11 on 25 October 2024 and took comments until 25 December 2024. The FAQ of VDE-AR-N 4105:2026-03 already refers to annex numbers in a forthcoming VDE-AR-N 4110:2026, because the medium-voltage rule is published after the low-voltage one. Until the new edition appears on the VDE FNN list as valid, design to 2023-09, record the edition named in the connection offer and ask the network operator how it will treat a project that is commissioned after the new edition is published.

VDE-AR-N 4105, 4110 or 4120: which rule applies?

The voltage at the network connection point decides first. The German technical connection rules are split by voltage level:

Two rules blur the boundary for small plants at medium voltage. VDE FNN's application aid of 10 March 2023 lets a medium-voltage project use VDE-AR-N 4105, with a higher-level decoupling protection, when its converter-connected (type 2) units and storage stay below 135 kW and the total stays below 270 kW. Above that, the 4110 route applies, with unit and plant certificates to 4110. The 2026 edition of VDE-AR-N 4105 extends its own process to medium-voltage plants with a total inverter power from 135 kW to 500 kW and an agreed feed-in of up to 270 kW, set with a medium-voltage parameter set.

The power class matters as well. Under the German thresholds approved by the Bundesnetzagentur on 24 April 2018, a generating plant is type B from 135 kW (about 150 kVA), type C from 36 MW and type D from 45 MW or at 110 kV and above. VDE-AR-N 4110 implements the type B and type C requirements.

Existing units count. The application aid states that existing generating units at the same connection point are included in the sum, so adding 100 kW of PV to a site that already has 200 kW of CHP is a 300 kW plant for this decision.

Unit, component and plant certificates

The evidence of electrical properties sits in three layers:

1. Unit certificate (Einheitenzertifikat): a type-tested inverter, generator or storage unit, tested to FGW TR3 and assessed to FGW TR8.
2. Component certificate (Komponentenzertifikat): a component that affects plant behaviour, such as the plant controller (EZA-Regler) or the protection device.
3. Plant certificate (Anlagenzertifikat): the whole plant at its connection point, issued by an accredited certification body from the unit and component certificates and the network operator's specifications.

Section 2 of the Elektrotechnische-Eigenschaften-Nachweis-Verordnung (NELEV) makes the plant certificate and a declaration of conformity the required evidence for type B and C plants. It exempts two groups of type B plants:

• a plant with a maximum feed-in of 270 kW at the connection point and a cumulative installed capacity of up to 270 kW, when every unit holds a valid unit certificate and every component a component certificate under the low-voltage connection rule; and
• a plant above 270 kW and up to 500 kW installed, connected at medium voltage or higher, whose feed-in is also limited to 270 kW, when a test report shows that the required decoupling protection is correctly installed and commissioned.

VDE FNN names three plant certificates:

A conditional certificate allowed provisional commissioning, with the complete evidence due within 18 months of commissioning the first unit. Projects that still hold one should track that date.

Worked example: four plants at a medium-voltage connection

The export limit on the second plant is part of the approved design. It has to be certified and protected against change, because the exemption depends on it. A limit that exists only as a setting in a monitoring system does not count.

Reactive power and static voltage support

A plant at medium voltage takes part in voltage control with reactive power. The network operator chooses the method in its questionnaire (form E.9, the Netzbetreiber-Abfragebogen) and sets the values for the connection. The methods are:

• a reactive power and voltage characteristic, Q(U);
• reactive power as a function of active power, Q(P), or a displacement factor characteristic, cos φ(P);
• a fixed displacement factor, cos φ; or
• a fixed reactive power in kvar or Mvar.

The voltage reference is Uc, the agreed supply voltage. VDE FNN's FAQ states that Uc is normally the nominal voltage of the network and is a fixed value, not a range. In the normal range of 90% to 110% of Uc, the plant must not reduce its active power in response to the voltage.

The choice depends on the network. Stromnetz Berlin's 2024 additions, for example, require plants in an open-ring 10 kV network to follow a Q(P) characteristic and plants in a closed ring or on a radial feeder to run at a fixed cos φ of 1. Read the operator's own TAB Mittelspannung for the values that apply.

Worked example: reactive power for a 2 MW PV plant

A PV plant has an agreed active power of 2,000 kW. The network operator asks it to be able to run at a displacement factor of 0.95 at full active power. The reactive power is P × tan(arccos 0.95):

Q = 2,000 kW × 0.3287 = 657 kvar

The apparent power at the connection point is P ÷ cos φ:

S = 2,000 kW ÷ 0.95 = 2,105 kVA

The inverters and the transformer must carry 2,105 kVA, not 2,000 kVA, or the plant has to reduce active power to make room for the reactive power. At 20 kV, 2,105 kVA is about 60.8 A per phase. Transformer magnetising and cable charging also produce or absorb reactive power between the inverters and the connection point, so the plant controller measures and corrects at the connection point, not at the inverters.

Active power: network operator signals and frequency response

Reduction by the network operator. VDE FNN's FAQ to section 10.2.4.1 says a reduction signal from the network operator must be applied directly, without a delayed ramp. Section 8.1 sets the priority: a reduction for network security (Netzsicherheitsmanagement) comes before frequency-dependent behaviour, and an increase in output at underfrequency comes before a direct marketer's set point. Section 9 of the EEG separately requires renewable and CHP plants of 100 kW and more to let the network operator read the actual feed-in at any time and reduce it remotely, until smart metering systems take over that role.

Overfrequency. Frequency-dependent active power reduction starts above a threshold frequency. RfG allows a threshold of 50.2 to 50.5 Hz; the network operator's TAB sets the value. The slope of the reduction is set in the rule and the operator's specification.

Mixed sites. For a site with generation, consumption and storage, VDE FNN states that reading the generation meter alone is not enough to show that a network security reduction was met. The evidence has to come from the connection point.

Protection and fault ride-through

Protection at a medium-voltage connection has several layers, each with a different owner:

• the network operator's protection and the customer's short-circuit protection at the transfer station;
• the higher-level decoupling protection (übergeordneter Entkupplungsschutz) at the connection point, which separates the plant from the network on voltage and, where the operator asks for it, frequency; and
• the decoupling protection at each generating unit.

VDE FNN's FAQ adds some practical points. Loss of the medium-voltage supply is detected from an auxiliary contact on the medium-voltage circuit breaker, not from the undervoltage stage. Frequency protection at the connection point is optional and applies only when the network operator requires it. The setting values come from the rule and the network operator's questionnaire, and the protection device carries its own certificate.

Plants must also ride through faults and support the voltage during them. VDE-AR-N 4110 distinguishes type 1 units, synchronous generators coupled directly to the network, from type 2 units, which include converter-connected PV, wind and battery systems. Type 2 units supply additional reactive current during a fault. Fault ride-through is proven by the unit certificate and the plant certificate, not by measurements on site.

Charging parks and other consumers

VDE-AR-N 4110 is not only a generation rule. A charging park, a cold store or a factory connected at medium voltage is a customer installation under the same rule. VDE FNN's FAQ to section 8.11 says charging equipment must be controllable in active power to the network operator's specification, and that a constant cos φ of 1 at the connection point applies when the operator sets no other method.

Controllable consumers on the low-voltage network, such as heat pumps and charge points that are not publicly accessible, fall under Section 14a EnWG instead, where the distribution network operator may limit their grid import in exchange for reduced network charges. Check the voltage level of the connection before choosing the rule.

Commissioning: declarations and forms

Annex E of VDE-AR-N 4110 contains the forms, which VDE FNN publishes as fillable files and network operators publish on their own sites. They include E.9 (the operator's questionnaire), E.11 (the commissioning declaration for generation plants and storage) and E.12 (the declaration of conformity for generation plants and storage).

VDE FNN's FAQ gives the timing:

Keep the approved single-line diagram, the certificate numbers, the protection settings and test reports, the plant controller parameter set and the network operator's acceptance together. A later change, such as adding a battery or replacing inverters, may count as a significant change that needs new evidence. VDE FNN's FAQ notes, for example, that a step-by-step modernisation exceeding 50% of P_AV,E makes later steps a significant change.

What to measure at a medium-voltage connection

Owner monitoring answers operational questions that the certified layers do not report to the owner:

Record active and reactive power per phase, voltage, frequency, the sign convention and a data quality flag, with timestamps from one clock. Log every reduction signal and set point the plant controller received next to the measured response, so a disputed event can be reconstructed. Use the three-phase power calculator and the transformer current calculator to check the expected currents before choosing current transformers.

The same pattern applies in other countries with different rules: G99 in Great Britain and CEI 0-16 in Italy. The renewable integration and grid stability guide explains why the network asks for voltage and frequency support at all.

Where EpiSensor fits

EpiSensor can provide owner-side measurement around a medium-voltage plant: electricity monitors on the low-voltage side of the transformers and on generation, storage and load feeders, and a Gateway running Edge that keeps a timestamped record on site and forwards approved data to the owner's platform. Edge can read the plant controller and inverters over Modbus to compare their reported values with independent measurements.

That layer does not certify a unit or a plant, act as the decoupling protection, replace the plant controller, provide the network operator's telecontrol connection or replace the billing meter. Fix the connection rule, the certificates and the operator's specifications first, then use System Builder to plan the operational measurement around them.