How does an AC fan work

The term "alternating current meter" refers to an energy meter for standard household single-phase alternating current with three-wire cabling. On the other hand, three-phase meters are required to record the energy flow at the five-wire connections for three-phase alternating current. As a calibrated measuring device, the alternating current meter is suitable for measuring points at apartment and house connections where the electricity supply is billed. AC electricity meters are mainly used as less expensive, uncalibrated devices, but also as intermediate meters for house, apartment or in-house energy measurement.

the essentials in brief

  • AC energy meter only measures the energy transfer (in kWh) at a two-pole connection consisting of phase and neutral.
  • A complete revolution can be precisely determined using a color marking on the turntable, which is visible from the outside and rotates when the current flows.
  • Mechanical alternating current meters are relatively complex and, above all, too inflexible for the time of day or load-dependent tariffs that are intended to promote energy saving. So-called intelligent meters (smart meters) are necessary for billing these tariffs,

Single-phase or three-phase electricity meter?

In principle, an alternating current meter only differs from a three-phase meter in that it is restricted to one phase. This means that it only measures the energy transfer at a two-pole connection made up of phase and neutral. In contrast, the three-phase meter can measure the energy flow over the three phases and the center conductor at a three-phase connection at the same time. In principle, it can also be used for energy measurement on a single-phase AC connection. However, because of the higher cost of the meter, this is usually not useful.

The previous standard: mechanical Ferraris single-phase electricity meters

Up until 2010, mainly mechanical alternating current meters for electricity billing, so-called Ferraris meters, were installed in Germany. This name is derived from Galileo Ferraris, the Italian inventor of the measuring principle. Typical of this type of meter is a thin aluminum disc that is visible from the outside and that rotates when the current flows. The speed of rotation depends on the currently transmitted power, so that each full rotation corresponds to a certain amount of energy.

For calibrated AC meters approved for electricity billing, this amount of energy is specified in revolutions per kilowatt hour on the nameplate. A complete revolution can be precisely determined using a color marking on the turntable. The instantaneous value of the electrical power can therefore be calculated with an alternating current meter by stopping the time for a full revolution of the disk.

Record power consumption and power feed-in with the Ferraris meter

With an alternating current meter with 480 revolutions per kWh, each revolution corresponds to approximately 2.08 Wh or 7.5 kJ. If the disk needs 25 seconds for one revolution, this corresponds to an instantaneous power of 7.5 kJ / 25 s = 0.3 kW or 300 watts. If the Ferraris meter does not have a backstop, this output can represent both a purchase of electricity and a feed-in, depending on the direction in which the disk rotates. With such an alternating current meter, billing for electricity purchase and feed-in for photovoltaic systems and the like is basically also possible.

However, your own electricity generation is then only offset against the electricity purchased and it is also not possible to record your own consumption. For this reason, the use of a bidirectional meter is generally cheaper for end customers with their own renewable electricity generation.

The current state of the art

With mechanical alternating current meters - for example the double tariff meter - more complex tariff models can be mapped. However, these meter variants are relatively complex and, above all, too inflexible for the time of day or load-dependent tariffs that are intended to promote energy saving. According to Section 40 of the Energy Industry Act (EnWG), electricity suppliers have had to offer such tariffs since the end of 2010. So-called intelligent meters (smart meters) that work fully electronically are required for billing these tariffs. In the case of new buildings and the modernization of house connections, Section 21 c of the Energy Industry Act prescribes the installation of such digital measuring points.

These measuring devices can also be designed as alternating or three-phase electricity meters. Counters with backstop, bidirectional and feed-in meters without backstop are provided for recording electricity consumption and feed-in. Intelligent meters also offer advantages for end customers thanks to the detailed options for recording energy consumption.


Photovoltaic systems generate direct current. An inverter makes the electricity usable for the household.


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