A driver sees a number on a screen and later a number on an invoice. Between the electrons leaving the connector and the amount being charged for them sits a chain of five links, and every one of them can shift the figure slightly or fail outright.
Two regulatory frameworks are usually mentioned in this context, and they are frequently treated as interchangeable when they are not. One governs the meter as an instrument. The other governs whether the number a customer is told can be verified afterwards. Knowing which does what turns a compliance question into an engineering one.
Five Links Between the Connector and the Invoice
The first link is the utility's own meter, at the point where the site takes supply. This is what the operator pays for, and it includes every loss and every auxiliary load on site.
The second is the site's internal distribution. Transformers, cable runs and switchgear consume a little of what passes through them, and that consumption belongs to the operator rather than to any individual session.
The third is the charging meter itself, mounted inside the unit. This is the point where energy becomes attributable to a specific connector and a specific session, and it is the point that most billing is based on.
The fourth is the path from that meter to the connector: rectification, the output cable, the pins, and for a cooled cable the coolant path alongside them. All of it dissipates a fraction of the energy that the meter has already counted.
The fifth is data. The meter value is read by the controller, formatted into a session record, transmitted to a backend, and turned into a line on an invoice — possibly after a tariff is applied, a time band is assigned and a rounding rule is chosen.
A driver comparing the energy the vehicle reports against the energy invoiced is comparing link four with a point upstream of link three. The gap between them is real, expected and largely unrelated to accuracy.
Meter Class and CT Ratio
A meter's accuracy is described by a class, and the class defines the maximum error permitted across a defined range of current and power factor. Two details decide whether that class is meaningful in a given installation.
The first is the current range. Accuracy classes apply within a specified window, and meters become less accurate at very low currents. An AC charging point that spends hours delivering a small top-up sits in precisely that region, which is why a meter that performs well on a DC unit at high output is not automatically the right choice for a lightly used AC point.
The second is whether the meter measures directly or through current transformers. Above a certain current, direct connection becomes impractical and the meter reads a scaled secondary signal. That introduces two new sources of error: the ratio of the transformers themselves, and the burden of the secondary wiring. A mislabelled ratio or a swapped phase produces a reading that is wrong by a fixed factor — consistent, plausible and completely incorrect.
Both details belong in the commissioning record rather than in the datasheet. The meter model and class, the transformer ratio, the wiring diagram and a photograph of the installation are the evidence a later dispute needs.
Sealing and Calibration
A meter used for billing is not simply a component with a good accuracy figure. It is an instrument whose conformity has to be established, and whose settings have to be protected from change afterwards.
Sealing is the visible part of that protection. A seal over the terminal cover, or over the configuration interface, demonstrates that the wiring and settings have not been altered since the unit was verified. Once a seal is broken — for a repair, a reconfiguration or an investigation — the instrument's status changes, and the documentation has to record why.
Calibration intervals are the other half. A meter that was verified at manufacture does not remain verified indefinitely in a market that requires periodic re-verification, and the interval is a matter of national rules rather than of product design. For an operator, this is a scheduling obligation: an uncalibrated meter can make historic invoices questionable, which is a much larger problem than the cost of the calibration visit.
The practical failure here is administrative rather than technical. A site can hold a fully compliant instrument, correctly installed and sealed, and still be unable to demonstrate its status because nobody recorded the seal numbers or the verification date.
What MID Covers
The Measuring Instruments Directive is European legislation that establishes requirements for meters used in transactions. A meter placed on the market under it carries a conformity assessment, and that assessment is what allows its readings to be used as the basis of a charge.
What it covers is the instrument: its design, its accuracy under defined conditions, its marking and its documentation. What it does not cover is everything around it. The current transformers, the wiring, the way the controller reads the meter, the arithmetic that applies a tariff, the rounding and the transmission to a backend are all outside its scope.
This distinction is the source of a common misunderstanding in procurement. A charger described as having a MID-approved meter is making a statement about one component. Whether the installation as a whole produces a defensible invoice is a separate question that involves the transformer ratio, the sealing record and the software path.
Where the energy figure is used for reimbursement or sub-billing, the meter is typically offered as a specified option rather than as standard equipment, because not every site needs a regulated instrument. AC units in this range can be supplied with a MID-approved meter for that purpose.
What Eichrecht Requires
German verification law approaches the problem from a different direction. Rather than regulating the instrument alone, it addresses whether the value a customer is charged for can be independently verified.
In practice this produces three requirements that hardware and software have to satisfy together. The value transmitted for billing has to match the value shown at the point of delivery. The measurement has to be traceable, so that a customer or an authority can reconstruct how the figure was produced. And the software that handles the values has to be transparent in the sense the framework requires, so that a change to the calculation cannot happen silently.
The second requirement is the demanding one. A charger that displays one number and transmits another, even by a rounding rule, fails on principle rather than on magnitude. A charger that displays a value but cannot produce a record explaining how it was derived fails the traceability test even if both numbers are identical.
This is why DC products intended for that market are specified with a compliance statement that covers the display, the measurement and the transmitted record together. The 480 kW hub host is specified this way for that market, and the statement is worth reading as a description of scope rather than as a badge.
Where Disputes Usually Start
Almost every metering dispute begins with two numbers that were not meant to be equal. A driver compares the vehicle's own figure with the invoice, and the gap — losses after the meter — is read as overcharging.
The second common origin is a unit in the wrong place. A site billed from the utility meter while sub-metering individual sessions finds that the totals do not reconcile, and the difference is distributed loss rather than error.
The third is a tariff applied to the wrong timestamp, which becomes visible when a session crosses a rate boundary and the record does not show which band was used. The fourth is a transformer ratio recorded incorrectly once and inherited by every subsequent invoice.
All four are answered by documentation rather than by argument. A session record that states the meter value, the timestamp, the tariff band applied and the resulting amount is defensible. A single total on an invoice is not, no matter how accurate the measurement behind it was.
A compliant meter is a component. A defensible invoice is a chain, and the chain is only as good as the record kept at commissioning.
The commissioning pack is therefore the deliverable that matters. Meter model, class and serial number. Transformer ratio and wiring diagram. Seal numbers and verification date. A photograph of the installation. A description of how the controller reads the meter and what it transmits. None of it is expensive to produce at the time and all of it is expensive to reconstruct later.
For sites where the meter is being audited after the fact rather than specified in advance, the sequence of checks is covered separately in the note on compliance retrofit auditing, which starts from the meter chain for the same reason. The documents a supplier is expected to provide are listed in the technical file on the download page.
Billing on energy you deliver yourself?
Start from the meter chain rather than from the meter. Class, ratio, sealing and the transmission path decide whether the invoice holds up.
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