Ofgem rejects transmission contestability code changes

Ofgem has rejected proposed changes to Britain’s Connection and Use of System Code that would have allowed some newly connected transmission users to build connection assets longer than 2km and widened the range of transmission connection work open to contestable delivery.

The regulator rejected both the original CMP330/374 proposal and its alternative, WACM1. CMP330 had been raised to allow new transmission connected users to construct connection assets longer than 2km, while CMP374 sought to extend contestability and give customers more flexibility over how those assets were delivered.

The two modifications were combined because they depended on the same wider legal and operational arrangements. That supporting framework was being developed through CMP414, which was intended to govern the relationship between customers, contractors, the Transmission Owner, and the wider transmission system when connection assets were built outside the conventional delivery route.

NESO withdrew CMP414 in June 2026. Ofgem concluded that implementing CMP330/374 without it would leave no coherent or workable basis for the intended arrangements, so neither the original proposal nor WACM1 was judged to better facilitate the applicable code objectives.

The decision closes this particular code route rather than removing the engineering case for greater contestability. Transmission connection projects can involve cables, substations, transformers, switchgear, protection, control equipment, communications, and civil works that serve one connecting customer. Allowing a customer to procure more of that work directly can change the delivery model, but it does not change the electrical duties imposed on the completed assets.

Longer connections increase those duties because the new equipment interacts with a larger part of the existing system. Cable impedance affects fault current and voltage behaviour, transformer characteristics influence fault levels and reactive power, and protection settings have to coordinate with equipment on both sides of the connection boundary. A design that functions as an isolated installation can still be unsuitable once connected to the transmission network.

Protection provides a practical example. Relays must identify faults and trip the correct circuit breakers quickly enough to protect plant, while remaining selective so healthy circuits stay energised. Extending a connection changes the impedance between the fault and the source, which can alter the current seen by protection devices and the time needed for different protection zones to operate.

Equipment ratings also have to reflect more than the customer’s expected import or export. Switchgear must withstand the available fault level, transformers must remain within thermal and insulation limits, and cables must carry their planned current without excessive heating. Earthing, voltage performance, harmonics, communications, and future network changes all influence whether the asset can be operated safely after construction.

The abandoned CMP414 framework was intended to provide the governance around those technical obligations. A Transmission Owner expected to operate an asset for decades needs defined rights over design assurance, inspection, testing, records, access, ownership transfer, liabilities, and defects. Without those arrangements, construction rights can be granted more easily than the resulting equipment can be accepted into the regulated network.

Ofgem has kept transmission self-build reform alive through a separate consultation opened on 7 October. That proposal would allow generation, storage, and demand customers to construct defined assets used only for their own connection before transferring the completed equipment to the relevant Transmission Owner.

The new route separates the policy objective from the rejected code package. Customers could gain more control over procurement and construction, but adoption would still require evidence that the equipment meets network standards and can be maintained safely. The wider transmission system would also remain a constraint: a customer can finish its own connection and still be unable to energise if upstream network reinforcement has not been completed.

Construction assurance therefore extends beyond the day of energisation. Cable joints, terminations, foundations, protection wiring, control systems, commissioning records, and equipment data all need to support future operation. Defects can remain hidden until loading changes or equipment ages, so a successful initial energisation is not enough to demonstrate that an asset is suitable for long term adoption.

Ownership transfer also changes responsibility for faults and maintenance. Once the Transmission Owner accepts an asset, it inherits obligations for inspection, outage planning, repair, and eventual replacement. The legal framework must therefore define which defects remain with the original builder, what warranties transfer, and what technical records are required before operational responsibility changes hands.

Ofgem’s rejection leaves CMP330/374 without effect and keeps the existing code arrangements in place. The regulator is pursuing the same broad objective through a replacement framework that addresses construction rights, adoption, technical assurance, and ownership together rather than approving a narrower modification after its supporting governance had disappeared.