P434 Implementation Working Group


Modification P434 ‘Half Hourly Settlement for UMS Metering Systems’ will require a period of mandatory Change of Measurement Class for NHH UMS Metering Systems. To ensure a smooth transition and support impacted parties, an Implementation Working Group (IWG) has been established.

Contact information

Operational queries
Contact your OSM

About IWG meetings
[email protected]

IWG Objectives

  • Share operational and implementation information that could be of value to others and that can feed into guidance issued by Elexon
  • Discuss and seek to resolve common issues with the migration and data cleanse
  • Provide feedback on the data cleanse template. Elexon will make changes to the template if necessary

Terms of Reference

Further information on the Group’s objectives, role and responsibilities can be found in the Terms of Reference.

Relationship with MHHS

Modification P434 ‘Half Hourly Settlement for UMS Metering Systems’ mandates that all NHH UMS Metering Systems must be (HH) settled via a new Change of Management Class (CoMC) process by the UMS Mandate Go-Live Date.

The UMS Mandate Go-Live Date is tied to milestone M11 of the Market-wide Half-Hourly Settlement (MHHS) Transition Timetable. The Timetable is currently subject to a MHHS Change Request.

The proposal is for M11 to move to April 2025.

P434 Data Cleanse Template

P434 also mandates a Data Cleanse activity, to start no later than 18 months prior to the UMS Mandate Go-Live Date.

We have created a set of FAQs to help with the work associated to P434.


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