Ferraris meter · Glossary

A Ferraris meter is an electromechanical electricity meter. It measures electrical energy with a rotating aluminium disc. In technical terminology it is called a meter with an induction measuring element. A current coil and a voltage coil generate alternating magnetic fields. These fields induce eddy currents in the disc, which produce a torque that corresponds approximately to the instantaneous active power. A braking magnet ensures that the rotational speed remains proportional to the power and that the disc does not keep accelerating. A mechanical roller register counts the revolutions and converts them into kilowatt hours. The meter therefore does not measure current in the physical sense (amperes), but the electrical energy drawn over time.

The central unit is the kilowatt hour. It corresponds to a power of one kilowatt drawn for one hour. The meter continuously adds up this quantity of energy and displays a meter reading, for example 24,386 kWh. The difference between two readings gives the electricity consumption relevant for billing. An example: if the meter reads 21,386 kWh on 1 January and 24,386 kWh a year later, 3,000 kWh were consumed. The disc, by contrast, only shows how much power is currently being drawn. If it turns quickly, many appliances or high-power appliances are running at that moment.

Meter constant: reading power from the disc

The rating plate usually states a meter constant, for example 75 revolutions per kilowatt hour. This allows the current power to be roughly estimated. If the disc takes 48 seconds for one revolution at this constant, the result is 3,600 divided by (75 times 48). That is 1 kW. If the marking on the edge of the disc can be read accurately, this is a simple household test, for example for standby consumption. It does not replace a calibrated power measurement. Only the running meter reading is used for billing.

Distinction from modern metering devices and smart metering systems

Every Ferraris meter is an electricity meter, but not every electricity meter is a Ferraris meter. Under the German Metering Point Operation Act (Messstellenbetriebsgesetz), a modern metering device is an electronic meter without its own communication unit. It displays actual consumption and actual usage time. In most cases it can also display historical daily, weekly, monthly and annual values. It can be securely integrated into a smart meter gateway. An intelligent metering system is a modern metering device that is connected to a communication network via a smart meter gateway. In general usage this is usually called a smart meter. Only this system delivers remotely transmitted, time-resolved measured values, such as quarter-hour values.

The Ferraris meter, by contrast, is a pure totalising meter. It stores no time series, has no digital interface and cannot be read remotely. For this reason, small customers with such meters are balanced using a standard load profile. Their actual consumption over time is therefore not measured but estimated using a typical profile. Designs with two registers for high and low tariffs, so-called dual-tariff meters, were possible. However, they only switched between fixed tariff periods, usually via a ripple control receiver or a time switch.

Why the lack of time resolution matters

For an annual bill, the total is sufficient. For the electricity system, however, it is increasingly important when the kilowatt hours occur. A kilowatt hour at midday with plenty of solar power has a different effect from a kilowatt hour on a windless winter evening with high load. Two households with an annual consumption of 3,000 kWh each can have very different load profiles. This depends, for example, on whether an electric car charges in the evening at high power or a heat pump runs mainly during cold hours. A Ferraris meter does not make this difference visible. A dynamic electricity tariff requires time-resolved measured values and therefore cannot be billed on a cost-reflective basis with a Ferraris meter. Time-variable grid charges and the value of flexibility also cannot be reliably represented with it.

Calibration law: accuracy, verification period and sampling

A common misconception is that old Ferraris meters are inherently inaccurate. That is too sweeping. They may only be used for billing within their period of calibration validity and must comply with the in-service error limits. Under Annex 7 of the German Measures and Verification Ordinance (MessEV), the following verification periods apply in Germany:

16 years for directly measuring single-phase and multi-phase AC meters with an induction measuring element, i.e. the usual household Ferraris meter. This also applies to dual-tariff meters.
12 years for meters with an induction measuring element that are used as transformer-operated meters, for example for larger connections.
For comparison: 8 years for AC meters with an electronic measuring element, including modern metering devices.

The verification period can be extended by a sampling procedure under § 35 MessEV. In this procedure, an entire lot of similar meters is tested on the basis of a sample. A year of manufacture more than 16 years ago therefore does not automatically mean that the meter is being operated unlawfully. Calibration validity ends early if the device no longer complies with the in-service error limits or if stamp marks are damaged. With the Ferraris meter, the problem is therefore above all the lack of time resolution and communication, not the counting of kilowatt hours as such.

Photovoltaics and the backward-running disc

In old Ferraris meters without a reverse-running lock, the disc can turn backwards if a photovoltaic system feeds more electricity into the grid than is consumed in the house. The meter reading then falls. This is not a permissible metering concept. Grid consumption and feed-in are billed separately and must therefore be recorded separately, as a rule with a bidirectional meter. The fact that the disc can physically turn backwards therefore does not permit netting at the house connection. Anyone connecting a generation system must have the meter adapted through the metering point operator.

Metering point operation and statutory replacement

The meter belongs to the metering point and falls under metering point operation. As a rule, the default metering point operator is responsible, unless a competitive metering point operator has been appointed. It installs the meter, operates it, organises the reading and makes the measured values available to authorised market participants. Replacement is therefore not a private decision about a household appliance.

The Metering Point Operation Act governs the phase-out of the Ferraris meter in Germany. Under § 29 paragraph 3, default metering point operators must equip metering points at fixed metering points of final consumers and plant operators with at least modern metering devices. This applies insofar as no intelligent metering system is provided for and the equipment is economically reasonable. The deadline ends at the end of 31 December 2032. For new buildings and major renovations within the meaning of the EU Buildings Directive, the equipment must be installed by the time the building is completed. The wording of the deadline was most recently amended by an act of 18 December 2025 with effect from 23 December 2025. The Federal Network Agency (Bundesnetzagentur) summarises the objective as follows: by 2032, all consumers are to have at least a modern metering device.

In certain cases a modern metering device is not sufficient. In those cases an intelligent metering system is provided for under the smart meter rollout. Under § 29 paragraph 1 MsbG, this applies, among others, to final consumers with annual consumption above 6,000 kWh. It also applies, together with a control device, to agreements under § 14a EnWG for a controllable consumption device such as a heat pump or a charging point. In addition there are generation plants above statutory capacity thresholds. Dates, quotas and price caps are likewise set out in the MsbG and have been amended several times. In individual cases, the version currently in force is therefore decisive.

Assessment

The Ferraris meter does not stand for incorrect measurement. It stands for a specific measuring logic: it reliably counts electrical energy as a total and leaves out the time of consumption. That suited an electricity supply with annual meter reading, fixed energy prices and standard load profiles. In a system with fluctuating renewable generation, electromobility, heat pumps and time-dependent prices, precisely this becomes the limit. The term helps to separate two perspectives clearly: consumption as an annual quantity and consumption as a time-effective variable for the grid and the market.

Sources

§ 29 MsbG – Ausstattung von Messstellen mit intelligenten Messsystemen, Steuerungseinrichtungen und modernen Messeinrichtungen — rewis (Gesetzestext des Messstellenbetriebsgesetzes); unbekannt. § 29 Abs. 1 Nr. 1 und 2, Abs. 3 MsbG
Änderung § 29 MsbG vom 23.12.2025 — buzer.de; 2025-12-23. § 29 Abs. 3 Satz 2 MsbG, alte und neue Fassung
Messeinrichtungen / Intelligente Messsysteme — Bundesnetzagentur; unbekannt. Abschnitt Moderne Messeinrichtungen
Allgemeines: Eichpflicht und Eichgültigkeit von Elektrizitätszählern — NZR (Zählerhersteller), Wiedergabe der MessEV Anlage 7; unbekannt. Abschnitt Eichgültigkeit
Eichfristen für Messgeräte nach der Mess- und Eichverordnung — Staatsbetrieb Mess- und Eichwesen Sachsen; 2022-06-23. Abschnitte 1 bis 5

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Edited by eCMS on 11.11.2026 19:47