System Operator Transmission Owner Code
All modifications to the System Operator Transmission Owner Code, tracked through their lifecycle. Administered by NESO.
How STC modifications work
The System Operator Transmission Owner Code (STC) governs the relationship between the System Operator (NESO) and the three Transmission Owners: National Grid Electricity Transmission, SP Transmission, and SSEN Transmission. It covers planning, construction, operation, and maintenance of the GB transmission system, including data exchange, outage planning, and the coordination of investment.
The modification process
The STC has two types of modification. Connection Modifications (CM) change the main body of the code. Procedure Modifications (PM) change the associated STC Procedures, which contain the detailed operational and planning processes. Both follow a similar governance route: a proposal is raised, assessed by a Workgroup or Amendment Panel, consulted on, and then decided by Ofgem or (for Self-Governance modifications) by the STC Amendment Panel.
Key concepts
- CM vs PM: Connection Modifications change the code itself. Procedure Modifications change the supporting STC Procedures. PMs are typically more operational and technical in nature.
- Self-Governance applies when a modification will not materially affect consumers, competition, or existing contractual arrangements. The Amendment Panel decides; parties can appeal.
- Cross-code impact means the modification affects other industry codes (Grid Code, CUSC, BSC). When this happens, the codes must be changed in coordination.