Migrating non-half hourly unmetered supplies metering systems to MHHS

Elexon is working to smooth the path to Market-wide Half Hourly Settlement (MHHS) implementation by supporting Parties that need to migrate more than 30,000 Non-Half Hourly unmetered supplies metering systems to MHHS.

P434 ‘Mandate to Half Hourly Settle the Non-Half Hourly Unmetered Supplies Metering Systems (UMS)’ requires a period of mandatory Change of Measurement Class activity for all Non-Half Hourly (NHH) UMS Metering Systems.

This needs to be completed by March 2025 (Milestone 11 in the MHHS Timetable). 

Steps to success on P434

  • Completing data cleansing activities prior to starting migrations 
  • New UMS connections to be settled Half Hourly from April 2024 and no reversion from HH to NHH from April 2024.

Your OSM will be in touch

To support the smooth transition, Elexon’s Operation Support Managers (OSMs) will be engaging with impacted Suppliers and Unmetered Supplies Operators (UMSOs) over the coming weeks to understand their migration plans and timescales.  

Support and guidance information

Through the support of the P434 Implementation Working Group, we have created a variety of materials on P434 activities: 

  • FAQs to give guidance and best practices on migration activities  
  • Process maps which will be available soon on the FAQ page to help Parties visualise the sequence of events for key activities 
  • A list of contacts for suppliers and UMSOs to help facilitate engagement. Parties can request this by contacting [email protected] 
  • P434 Reporting – which will provide data on migration performance, including Metering System ID (MSID) counts and energy volumes, once migration gets underway. 

Background on P434

See the P434 webpage for all of the background documents related to the Modification.


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