NESO raises STC modification PM0124 to revise Expansion Constant & Expansion Factor data requirements following CMP315/CMP375

NESO submitted STC modification proposal PM0124 on 14 February 2023, a consequential change to revise STC data requirements, templates and processes to reflect new methodology for calculating the Expansion Constant (EC) and Expansion Factor (EF) arising from CUSC modifications CMP315 and CMP375, and to incorporate 'Lessons Learned' from the RIIO-2 EC & EF re-calculation. The proposal was approved for STCP processing on 22 February 2023 and is now awaiting a Panel decision on the governance route.

EC and EF values directly influence the locational signal embedded in TNUoS tariff calculations, which apply to all Users paying TNUoS charges, ESO, and Onshore/Offshore Transmission Owners. Updating the underlying data requirements and methodology affects how transmission investment and network growth are reflected in transmission charges, with a stated High impact on affected parties.

PM0124 is a procedural/data-consequential modification rather than a substantive charging methodology change itself—the substantive EC/EF calculation methodology changes are being progressed through CUSC modifications CMP315 and CMP375. PM0124's role is to align STC data submission requirements, templates and TO reporting processes with whatever new methodology CMP315/CMP375 ultimately adopt. Because implementation is explicitly TBC and pending Panel determination on governance route, this event is currently in early regulatory review with no confirmed timeline; its eventual effect on TNUoS tariff locational signals will depend on the parallel CUSC process outcomes.

System Operator Transmission Owner Code (STC), in conjunction with Connection and Use of System Code (CUSC)

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