In service testing of gas and electricity meters
The Measuring Instruments Directive (MID) is a European Directive (2004/22/EC) that covers a number of different measuring instrument types including gas meters and active electrical energy meters. The aim of the MID is to create a single market in measuring instruments for the benefit of manufacturers and, ultimately, consumers across Europe.
In the UK, the MID is implemented by Regulations for the different instrument types and these are available to download from the following website: http://www.legislation.gov.uk/uksi
For gas and electricity meters the relevant legislation is:
- The Measuring Instruments (Gas Meters) Regulations (SI 2006/2647)
- The Measuring Instruments (Active Electrical Energy Meters) Regulations (SI 2006/1679)
The MID only applies up to the point that meters are first placed on the market and thereafter they are covered by the existing national provisions. Gas and electricity meters that are put into use in accordance with these Regulations are “deemed” to be stamped as required by Section 17 of the Gas Act 1986 and approved and certified as required by Schedule 7 of the Electricity Act 1989.
However, this does not apply if the error of measurement exceeds that prescribed in the Regulations. MID meters that are not deemed to be stamped (gas) or approved and certified (electricity) do not meet the requirements of the Gas and Electricity Acts and may therefore not be used for billing.
Background
The Industry Metering Advisory Group (IMAG), sponsored by ELEXON and OFGEM, set up the In-Service Testing and Post-MID Expert Group (IST1), to develop proposals for the in-service accuracy monitoring of MID approved domestic type gas and electricity meters. A further Expert Group (IST2) was subsequently established to develop additional proposals to ensure the other legislative requirements aside from meter accuracy were also covered.
The combined proposals of these Groups were published in the IST 1/2 Report that was accepted by IMAG and OFGEM in 2008. These proposals set out a methodology based on sample testing whereby energy suppliers and asset owners can demonstrate they are fulfilling their statutory obligation to keep their meter populations in proper order for correctly registering the quantities of gas and electricity consumed.
A further Expert Group (IST3) was then established to consider the costs of the IST scheme and possible governance arrangements. The findings of this Group were published in the IST 3 Report in 2009. IMAG and NMO then published a joint consultation on the governance options and, following the transfer of responsibility for the metrological performance of gas and electricity meters from Ofgem to NMO, it was agreed that NMO would assume responsibility for governance of the IST scheme.
What is IST?
IST is a national sampling scheme for gas and electricity meters based on the British Standard BS 6002-2:2007 (Sampling Procedures for Inspection by Variables).
NMO contact asset owners on an annual basis to request information about the meters in their portfolios, including manufacturer, model number, year of installation, and population size. NMO then collate this information to obtain a list of meter samples required for in-service testing. The sample sizes are allocated in proportion to the overall population size as detailed in the IST handbook and the British Standard.
Asset owners are requested to submit the required number of samples to approved IST test stations for laboratory testing. Finally, NMO collate the test results and assess the performance of individual meter populations using the agreed assessment criteria.
IST will take place at regular intervals throughout the anticipated lifespan of a gas or electricity meter. Meters may continue in-service for as long as they conform to the Regulations, while meters that no longer conform will need to be removed from service. IST therefore forms an important part of consumer protection by ensuring that only meters that operate within the prescribed limits of accuracy are used for consumer billing.
Scope of IST
The IST methodology was developed for domestic type meters approved under the European Measuring Instruments Directive (MID). Domestic type meters are defined as those with a maximum capacity of 6m3/hour (gas) and whole current, single phase meters (electricity).
NMO is now considering how the IST methodology may be extended to meters approved under UK national legislation. IST can assist asset owners to manage their meter portfolios during the transition to “smart meters”.
In the future it may be possible to extend the IST methodology to cover non-domestic meters (i.e. larger meters installed in industrial and commercial premises). However the statistical process detailed in the IST handbook will need to be modified to account for the much smaller populations of these meters.
Implementation
NMO has established a further Expert Group (IST4) to implement the IST scheme. This group is open to all interested parties including energy suppliers, asset owners, trade organisations and meters manufacturers.
NMO is currently developing an “IST handbook” to summarise the testing requirements developed in the IST 1/2 and IST 3 Reports. The handbook will also include details of IST test stations that have been approved by NMO for the in-service testing of gas and electricity meters. The latest version of the IST handbook will be available from the NMO website shortly.
For further information on IST and/or application for membership of the IST4 group please contact: michael.worrell@nmo.gov.uk.
