Issue 3/2001 of Metering International reported on progress with development of the European Measuring Instruments Directive (MID) – the putting into use of a wide range of measuring instruments subject to metrological controls, including electricity, gas and water meters. The article suggested that ratification of the MID was imminent, but in fact it was not agreed until March this year. European member states must now transpose the MID into their own laws and apply its provisions as from 30 October 2006.

European directives set legal requirements with which member states (MSs) must comply, so as to harmonise practices across Europe. The European Commission, the administrative body of the European Union (EU) can propose directives which are then discussed and agreed at Council (the main EU decision-making body) or European Parliament level or – as in the case of the MID – both. The Commission consults appropriate bodies to produce a proposal which is likely to be accepted; for the MID, this process involved representatives of both legal metrology bodies of MSs and of industry (the European trade associations for the relevant sectors). The final Commission proposal for the MID went to Council in September 2002 and was adopted. This was the start of a discussion process, during which the draft was amended until all Council and Parliament representatives were able to report a common position (ie agreement to it).


The MID’s key objective is to remove barriers to trade in measuring instruments. It sets out requirements which must be complied with before instruments can be placed on the European market or put into use. These are stated as generic essential requirements (ERs) with which all instruments must comply, and instrument-specific ERs in individual Annexes.

The main principles are that to assess conformity of products with the MID, MSs may designate notified bodies (NBs) – essentially test houses in that particular MS which are independent of its legal metrology organisations. Not all MSs will have NBs for each category of instrument, but the MID allows approval completed in one MS to be equally valid in another. In general, manufacturers will submit new products to the NB of their choice in any MS for confirmation that the product conforms; this product may then be CE marked and sold in that and any other MS, which must accept the mark as proof of conformity.

The regime for conformity assessment is flexible and can range from the NB directly carrying out tests, through the NB accepting the results of tests carried out within a quality assurance regime, to full declaration by the manufacturer of conformity of both design and production. The MID is a ‘new approach’ directive, which means that the ERs are broad and may need interpretation to assist assessment of compliance. This is usually done through European standards (ENs) produced under a mandate from the Commission. Compliance with such standards is deemed a fast track to conformity. The MID also establishes a Measuring Instruments Committee (MIC) which has powers to agree normative references which presume conformity, and to amend the requirements of the instrument-specific Annexes.

The MID applies only to new products and is not retrospective so, in the case of electricity meters, it will not apply to refurbished meters put into service after it comes into force, nor to existing meters on circuit. Also, it does not directly refer to in-service requirements such as the overall accuracy limits which most European Member States prescribe. A transition period is allowed so that instruments satisfying the rules applicable before October 2006 may still be placed on the market for a period of time under defined conditions.


The version of the MID adopted in September 2002 was generally satisfactory to the electricity meter industry, except for the specific Annex MI-003 for electricity meters, which was considered completely unworkable. Redrafting it was a major priority. During consultation the Commission had been assisted by a working group of WELMEC (the Western European Legal Metrology Committee) and this group was reconvened to advise Council on technical changes.

Revision of MI-003 through this group did not go well; at the end of 2002 agreement had still not been reached and progress of the MID itself was being held up. UK legal metrology representatives (National Weights and Measures Ltd - NWML) stepped in and offered to host intensive meetings, which resulted in an acceptable version finally being agreed. This was sent to Council in March 2003 and, with some minor amendment, is now in the published Directive.

Definitions Alignment of definitions for electromechanical and static meters
Operating conditions To be specified by the manufacturer within set limits

Three Classes, Maximum Permissible Errors at Imax and between+5 to +30 °C being:

A: 3.5%
B: -2%
C: 0.7%

Disturbances of long duration Permitted effect on accuracy specified
Disturbances of long duration Recovery criteria specified
Miscellaneous Error not to exceed 10% below rated operating voltage.
Display to not reset within 4000 hours and to be available for four months after loss of supply.
Within specified voltage range, no registration if no current.

[NOTE: There are other requirements within Annex 1 which apply]


Publication of the MID is not the end of the process, and several strands of work remain.

1. Transposition of the MID into the laws of individual MSs
There is a two-year window for MSs to adopt the provisions of the MID into their metrology laws. As these laws vary between states, it is not possible to give a useful generic view of the MID’s likely impact. A metering group of EURELECTRIC – the trade association for the European electricity utilities – met recently and will seek to give utilities an overview on progress within each MS. The group will update a survey of the legal metrology practices across Europe, which will identify the starting points to help members track changes as work proceeds.

In the UK the transposition work will be done through NWML, advised by the regulator Ofgem, which has legal metrology responsibilities for both electricity and gas meters.

Ofgem has set up its own advisory group to identify drafting requirements; the group includes utility and manufacturer representatives.

2. Production of normative documents to assist presumption of conformity
A major long-standing concern of industry with the MID has been that the new approach works in a ‘green field’ situation. However, as far as electricity meters are concerned, a comprehensive series of European standards based on international (IEC) standards has been in existence for some time. Both sides of industry have invested considerable resources to produce criteria within these standards that form an acceptable balance between performance and price. During the drafting of MI-003, industry delegates were largely successful in inserting rather more detail than Commission officials were happy with – such detail of course aligning with the criteria in existing standards! The intention was that any mandate to CENELEC (the European standards body) as regards the MID would allow relatively minor modification to these existing standards to produce suitable supporting documents.

However, the MID is unusual in allowing for two ways in which supporting standards can be produced. The Commission may:

  • Issue a mandate to relevant standards bodies (for electricity meters this is CENELEC) under normal procedures relating to new approach directives (Article 13.1).
  • Identify and list parts of normative documents produced by OIML (an international organisation of legal metrology representatives) which presume compliance with the ERs (Articles 13.2 and 16.1).

The Commission has now issued an enquiry for a mandate, to which CENELEC Technical Committee 13 is preparing a response in respect of electricity meters. This will propose the production of three new European standards based on IEC 62052-11, 62053-11 and 62053-21, and also further work within IEC on standards relating to acceptance, inspection and reliability, which will then be adopted by CENELEC. A timetable for this work is also included, so that the standards will be in place before the MID comes into force.

Industry has been concerned about this dual path within the MID, which could lead to duplication of work and/or differing requirements which would be confusing. It is unfortunate that an attempt to produce a memorandum of understanding between CENELEC and OIML as to who should do what failed. In theory, the Commission should not act until advised by the MIC, and the MIC cannot be set up until the MID comes into force. However, OIML is conscious of its potential role and has already started work on review of its Recommendation 46 on electricity meters. Some criteria additional to and different from the CENELEC standards have already emerged.

The MID comprises the following:

  • A recital, being legal and political justification for its issue.
  • The body, covering inter alia scope, objects, status of the Essential Requirements, marking, conformity assessment including technical documentation required, designation of and criteria for Notified Bodies, status and production of normative references, the Measuring Instruments Committee and its functions, market surveillance, transitional provisions and entry into force.
  • Annex I – generic essential requirements applying to all instruments, including classes of climatic and electromagnetic environments.
  • Annexes A-H1 – details of conformity procedures. These include type tests, initial verification tests and declarations by a manufacturer based on quality assurance concepts.
  • Annexes MI-001 to MI-010 – specific ERs for particular types of instrument. Annex MI-001 refers to water meters, MI-002 to gas meters, MI-003 to electricity meters and MI-004 to heat meters.

3. Software requirements of the MID
The MID has requirements about software used in measuring instruments – for instance to separate software relating to legal metrology functions and protect it from unauthorised access or attack. WELMEC established a working group (WG7) to identify specific requirements and make recommendations to NBs about how software conformity could be assessed. It produced a general guide (WELMEC 7.1) and some specific proposals for simple electricity meters (WELMEC 7.2).

However, in 2001 further work was passed to a thematic network – a consortium of interested parties funded by the EU – on the basis that this would speed up the production of documentation, but with the proviso that WG7 should be kept aware of its output. The network is due to present its report in October this year.

4. Consistency of assessment
The MID does not harmonise legal metrology requirements across MSs, and the role of WELMEC has always been to exchange information to promote consistency of practice within the different metrology provisions in different MSs. Although each MS will exercise a surveillance role within its borders to ensure that NBs are complying with the MID requirements, there could be problems with differences of approach. For instance, it would be unfortunate if one NB had the reputation of being ‘easy’ as regards obtaining compliance – manufacturers would tend to favour this NB and the confidence of purchasers would be undermined. WELMEC would seem to have an important and continuing role to play in promoting consistency, in conjunction with the MIC.

The MID has been a major project which will impact on 25 countries within Europe. It has taken longer than expected – first discussions began around 1988 – but is now on the final lap to successful implementation.