MID electricity meters — accuracy classes A/B/C under EN 50470 and Directive 2014/32/EU

The [guide on current transformer measuring class and burden in indirect kWh metering](/guides/practical/stroomtransformator-meetklasse-burden-kwh-meting) covers the accuracy of the current transformer in an indirect metering setup. The energy meter itself — the device that registers the final kWh value and that is used for billing — falls under its own legal framework: the Measuring Instruments Directive (MID, Directive 2014/32/EU). This guide addresses what MID means for the energy meter, and the accuracy classes A, B and C that go with it.

What MID regulates and why it matters

Directive 2014/32/EU regulates the requirements for measuring instruments used for legal purposes — in the context of energy meters this almost always means: metering that is used for billing. For electricity meters, the specific requirements (accuracy class, maximum permissible error, permitted effect of disturbances) are laid down in Annex MI-003 of the directive. A meter that falls under MID carries the CE marking together with the additional metrology marking (an M with the year of conformity assessment) and a notified body number. This is relevant for any installer fitting a sub-meter for a situation where that measurement is used to bill a third party — for example an EV charger with recharged electricity costs, a sub-let commercial space, or an on-site meter for a solar installation with feed-in. A meter installed purely for the owner's own insight (for example a sub-meter in an energy monitoring system with no billing to third parties) does not need to comply with MID.

EN 50470 as the harmonised standard

EN 50470-1 (general requirements, tests and test conditions) together with EN 50470-2 (electromechanical meters) or EN 50470-3 (static meters) forms the harmonised standard through which a manufacturer can demonstrate conformity with MID. These standards are similar in structure to the better-known IEC 62053 series (see also the current transformer guide above, which refers to IEC 61869-2 for current transformers), but are written specifically for the direct legal context of MID.

The accuracy classes A, B and C

EN 50470-1 distinguishes three accuracy classes, each corresponding to a class from the IEC 62053 series:

Class A: corresponds to class 2 of IEC 62053-21 — the widest permissible measurement error of the three MID classes, typically applied for simple, small-scale applications.
Class B: corresponds to class 1 of IEC 62053-21 — a stricter permissible measurement error than class A, and in practice the most common class for regular residential and small commercial connections.
Class C: corresponds to class 0.5S of IEC 62053-22 — the strictest of the three MID classes, with the lowest permissible measurement error, and typically applied where greater accuracy is required legally or contractually (for example large-consumer connections with indirect metering via current transformers).

A meter only needs to comply with one of these three classes to be considered MID-conform; which class applies depends on the intended use and any contractual or national requirements on top of the MID minimum requirements.

Practical relevance

For the installer, the key control point is not calculating a measurement error, but verifying that the correct meter with the correct marking is being fitted for the intended application: a meter without CE/M marking and a notified body number is not suitable for billing a third party, regardless of how accurately the device functions internally. For a sub-meter for an EV charger with recharged costs, or an on-site meter that an energy supplier or landlord uses for settlement, it must first be established whether MID conformity is legally required for that specific application — this varies by situation and by national implementing legislation, and is not purely a technical choice for the installer.

Common mistakes

Fitting a non-MID-certified sub-meter for an application where a third party is billed — for example a cheap DIN-rail kWh meter without CE/M marking for an EV charger with recharged electricity costs.
Confusing "accurate enough for own use" with "MID-compliant" — a meter can be technically accurate without the formal metrological certification and marking that MID requires for legal billing.
Assuming that any meter with an IEC 62053 class designation is automatically MID-compliant — the IEC 62053 series and the EN 50470 series are related but separate normative frameworks; the MID marking (CE + M + year + notified body number) is the formal proof of conformity, not the class designation alone.
Keeping the same class when replacing a faulty meter without checking whether the application now requires a stricter class — for example after extending a connection into a large-consumer situation with indirect metering.