The terms I use in my published work, what I mean by them, and where each one comes up. It grows as new terms appear in the work. Where a term has a primary source, it is linked.
GW-months Net movement Row-level and project-level date movement Derived residual Counting basis Snapshot provenance TEC Register Embedded Register (NESO) Embedded Capacity Register (ECR) Interconnector Register Project Number (PRO-nnnnnn) Tranche Gate 1 and Gate 2 Countersignature Accepted to connect Unique Site Identifier Maximum Import Capacity (MIC) Rated IT load TMO4+ Clean Power 2030 User Commitment (CMP192) Wider Cancellation Charge Queue management milestones (CMP376) Progression Commitment Fee (CMP448) CMP470 Curate Data Centre Service and Enterprise Basis ASTI TNUoS Transmission demand residual DUoS BSUoS RIIO-3 and RIIO-ED2 Regulatory Asset Value (RAV) Private wire CUSC DCUSA National Terms of Connection NESO DNO Transmission owners (NGET, SPT, SHET) Ofgem
GW-months
The measure I use for connection-date movement in the TEC tracker: the capacity of each agreement whose date moved, multiplied by the number of months it moved, added up across the register. Moves to a later date count as negative, moves to an earlier date as positive. A running total is carried from edition to edition.
Used in: TEC tracker, Edition 2 · TEC tracker, Edition 4 · TEC tracker, Edition 5
Net movement
The change in total contracted capacity on a register between two files, after joiners and leavers. Where capacity has moved from one NESO register to another, I record it as a transfer rather than as capacity leaving the queue.
Used in: TEC tracker, Edition 2 · TEC tracker, Edition 3 · TEC tracker, Edition 4 · TEC tracker, Edition 5
Row-level and project-level date movement
Two ways of counting date movement. Row-level compares the date on each register row between files. Project-level groups a project’s rows together, so it also catches capacity moved between tranches when no row’s date changes. From Edition 5 the tracker reports both.
Used in: TEC tracker, Edition 4 · TEC tracker, Edition 5
Derived residual
A figure obtained by subtracting one register column’s movement from another’s. It is arithmetic, not a measurement: the register does not record what happened to the capacity it represents, so I never describe it as a withdrawal.
Counting basis
The stated rule for how a total was added up: which column, which files, whether rows were deduplicated. I give it wherever a total appears, because the registers allow more than one defensible answer.
Used in: ECR tracker, Edition 1 · Four gigawatts left a connection register
Snapshot provenance
NESO overwrites each register file when it publishes the next, so a file not downloaded on the day is gone. The publication date in the filename is the only record of which snapshot a figure comes from, which is why downloaded files are never renamed.
TEC Register
NESO’s published list of projects holding transmission connection agreements, giving each project’s capacity (Transmission Entry Capacity, in MW), connection site, connection date and Gate status.
Source: NESO, TEC Register
Used in: TEC tracker, Edition 2 · TEC tracker, Edition 3 · TEC tracker, Edition 4 · The seven projects the NAO singled out · TEC tracker, Edition 1 · Grid connection dates are sliding · The TEC Register doesn’t show connections reform yet · Seven projects, 4.2 GW, gone from the register · Connection dates and grid upgrades · TEC tracker, Edition 5 · Why does CMP470 make sense? · Why does CMP470 make sense? (post)
Embedded Register (NESO)
NESO’s register of embedded, distribution-connected projects in Scotland that have a bearing on the transmission system. It covers Scotland only and is not additive to the DNO Embedded Capacity Registers.
Source: NESO, Embedded Register
Used in: TEC tracker, Edition 4 · Four gigawatts left a connection register
Embedded Capacity Register (ECR)
The register each distribution network operator publishes of generation and storage schemes connected, or accepted to connect, to its network, in a common template set under DCUSA. The six DNO groups each publish their own, in their own format.
Source: DCUSA
Used in: ECR tracker, Edition 1 · Four gigawatts left a connection register
Interconnector Register
NESO’s register of interconnector connection agreements. An interconnector leaving the TEC Register may have moved here, so the tracker checks this register before counting one as gone.
Source: NESO, Interconnector Register
Used in: TEC tracker, Edition 4
Project Number (PRO-nnnnnn)
The identifier on the TEC Register that the tracker uses as its row key, compared from file to file. Where a project is split into tranches, each tranche sits on its own row under the same project.
Source: NESO, TEC Register
Used in: TEC tracker, Edition 4
Tranche
A portion of a project’s capacity carried on its own register row, with its own connection date.
Used in: TEC tracker, Edition 4 · TEC tracker, Edition 5
Gate 1 and Gate 2
The two stages of the reformed connections process. A project at Gate 2 has met the readiness and strategic alignment tests and holds a confirmed queue position; a project at Gate 1 has not yet. The tracker counts agreements that gain a Gate label in each week’s file.
Source: NESO, Connections Reform
Used in: TEC tracker, Edition 2 · TEC tracker, Edition 3 · TEC tracker, Edition 4 · Five controls on the connections queue · TEC tracker, Edition 1 · The TEC Register doesn’t show connections reform yet · TEC tracker, Edition 5 · Why does CMP470 make sense? · Why does CMP470 make sense? (post)
Countersignature
The customer’s signature on a connection offer, which completes the agreement. “A Gate recorded on countersignature” in the tracker means a Gate label appearing on an agreement in that week’s file.
Used in: TEC tracker, Edition 3 · TEC tracker, Edition 4 · TEC tracker, Edition 1 · The TEC Register doesn’t show connections reform yet
Accepted to connect
The ECR status of a scheme that has accepted a connection offer but is not yet energised. The ECR tracker sums Accepted to Connect Registered Capacity as each operator publishes it.
Used in: ECR tracker, Edition 1 · Four gigawatts left a connection register
Unique Site Identifier
The ECR field that the governing template defines as an identifier that “distinguishes each entry uniquely rather than use site name”. Mandated since February 2026; not yet published consistently by all six DNO groups.
Source: DCUSA
Used in: Four gigawatts left a connection register
Maximum Import Capacity (MIC)
The import capacity agreed in a site’s connection agreement, and the measure against which some regimes set their thresholds and under which the National Terms of Connection allow unused capacity to be reviewed.
Source: ENA, National Terms of Connection
Used in: 72.8 GW requested, 4 GW connecting, 1.4 GW drawn · Six rulebooks set a data centre size line
Rated IT load
The power rating of a data centre’s IT equipment, excluding cooling and other site load. It sits below the site’s connection capacity, which is why a scheme can fall on different sides of thresholds set on each.
Used in: Six rulebooks set a data centre size line · Ofgem’s data centre milestones may bite at 1MW
TMO4+
The reformed, gated connections process for GB, which sorts projects into Gate 1 and Gate 2 and tests readiness and fit against Clean Power 2030 at entry.
Source: NESO, Connections Reform
Used in: Five controls on the connections queue
Clean Power 2030
The government’s action plan for a clean power system by 2030, published December 2024. It sets the capacity ranges that connections reform tests projects against.
Source: DESNZ, Clean Power 2030 Action Plan
Used in: Five controls on the connections queue · The seven projects the NAO singled out
User Commitment (CMP192)
The CUSC arrangement under which a project carries part of the cost of the network built for it, through liability that grows towards energisation.
Source: NESO, CMP192
Used in: Five controls on the connections queue · Why does CMP470 make sense?
Wider Cancellation Charge
The charge a project faces under User Commitment if it terminates, reflecting the wider network works built on its behalf.
Source: NESO, CMP192
Used in: Five controls on the connections queue
Queue management milestones (CMP376)
Progress milestones written into the CUSC in 2023. Projects that miss them can be removed from the queue.
Source: NESO, CMP376
Used in: Five controls on the connections queue · Ofgem’s data centre milestones may bite at 1MW
Progression Commitment Fee (CMP448)
A fee on projects between Gate 2 and Milestone 1, approved December 2025. It stays dormant unless terminations pass a set threshold.
Source: NESO, CMP448
Used in: Five controls on the connections queue
CMP470
A proposed CUSC modification introducing an Oversubscribed Technologies Commitment Fee. It applies when a technology’s capacity in the queue exceeds its government target by more than 50%. Ofgem published a minded-to consultation on 17 September 2026.
Source: Ofgem, CMP470 consultation
Used in: Five controls on the connections queue · Why does CMP470 make sense? · Why does CMP470 make sense? (post)
Curate
Ofgem’s 2026 consultation on data centre connection reforms, published 29 July 2026, covering commitment fees and queue management milestones for data centres.
Source: Ofgem, Proposed data centre connection reforms
Used in: Ofgem’s data centre milestones may bite at 1MW · Six rulebooks set a data centre size line · Curate consultation response · Flexible Hybrid Grid Connection · Why does CMP470 make sense?
Data Centre Service and Enterprise Basis
Definitions in the draft CUSC text consulted on under Curate. A Data Centre Service is a facility at 1 MW or above, or 10 MW where it is on an Enterprise Basis, meaning it serves only its owner’s own undertaking.
Source: Ofgem, Proposed data centre connection reforms
Used in: Ofgem’s data centre milestones may bite at 1MW · Six rulebooks set a data centre size line · Curate consultation response
ASTI
Accelerated Strategic Transmission Investment: Ofgem’s 2022 framework for fast-tracking large onshore transmission projects needed for 2030.
Source: Ofgem, ASTI decision
Used in: The seven projects the NAO singled out · Connection dates and grid upgrades
TNUoS
Transmission Network Use of System charges: what users pay for the transmission network, set annually by NESO.
Source: NESO, Final TNUoS Tariffs 2026/27 (PDF)
Used in: What a data centre actually buys from the grid · What sits inside the data centre price gap
Transmission demand residual
The fixed part of transmission charges for demand sites, charged per site per day by band rather than by the power drawn. In the top band for 2026/27 it is £20,829.24 a day.
Source: NESO, Transmission Demand Residual guidance (PDF) · NESO, Final TNUoS Tariffs 2026/27 (PDF)
Used in: What a data centre actually buys from the grid · The haulage deal nobody would sign · What sits inside the data centre price gap · Ofgem built a network charge that is very hard to avoid
DUoS
Distribution Use of System charges: what customers pay for the local distribution network. Since April 2023 they also carry the reinforcement costs no longer charged to connecting demand.
Source: Ofgem, Access and Forward-Looking Charges SCR decision
Used in: What a data centre actually buys from the grid
BSUoS
Balancing Services Use of System charges: the cost of keeping supply and demand matched in real time, charged to final demand only since April 2023.
Used in: What a data centre actually buys from the grid · What sits inside the data centre price gap
RIIO-3 and RIIO-ED2
Ofgem’s price controls for the network companies. RIIO-3 covers transmission from 1 April 2026; RIIO-ED2 covers distribution. Each sets allowed revenue, including an allowed return on equity, for a five-year period.
Source: Ofgem, RIIO-3 Final Determinations · Ofgem, RIIO-ED2 Final Determinations
Used in: What a data centre actually buys from the grid · The haulage deal nobody would sign
Regulatory Asset Value (RAV)
The regulated value of a network company’s asset base. Spending added to it (“slow money”) earns a return and is recovered over the assets’ lives; spending recovered in the same year is “fast money”.
Source: Ofgem, RIIO-ED2 Final Determinations
Used in: What a data centre actually buys from the grid · The haulage deal nobody would sign
Private wire
A direct line from nearby generation to a site, bypassing the network for the power it carries. It avoids usage-based charges on that power but not the fixed residual charges, if the site stays grid-connected.
Source: Ofgem, Targeted Charging Review decision
Used in: What a data centre actually buys from the grid · The haulage deal nobody would sign · What sits inside the data centre price gap
CUSC
The Connection and Use of System Code: the industry code governing connection to, and use of, the GB transmission system. Changes to it are made through numbered modifications (CMPnnn).
Source: NESO, CUSC
Used in: Five controls on the connections queue · Ofgem’s data centre milestones may bite at 1MW
DCUSA
The Distribution Connection and Use of System Agreement, the equivalent multi-party agreement for the distribution networks. It governs the Embedded Capacity Register template.
Source: DCUSA
Used in: Four gigawatts left a connection register
National Terms of Connection
The standard terms, published through the Energy Networks Association, on which distribution-connected customers are connected. Section 3 includes the clause allowing a network operator to propose reducing unused import capacity.
Source: ENA, National Terms of Connection
Used in: 72.8 GW requested, 4 GW connecting, 1.4 GW drawn · Great Britain’s data centre queue, in three numbers
NESO
The National Energy System Operator, which runs the GB transmission system, administers the CUSC and publishes the TEC, Embedded and Interconnector Registers.
Used in: TEC tracker, Edition 2 · TEC tracker, Edition 3 · TEC tracker, Edition 4 · 72.8 GW requested, 4 GW connecting, 1.4 GW drawn · TEC tracker, Edition 5 · Why does CMP470 make sense?
DNO
Distribution network operator. Six DNO groups run Great Britain’s fourteen distribution licence areas and each publishes its own Embedded Capacity Register.
Used in: ECR tracker, Edition 1 · Four gigawatts left a connection register
Transmission owners (NGET, SPT, SHET)
The companies that own the transmission network in their areas: National Grid Electricity Transmission in England and Wales, SP Transmission in southern Scotland, and Scottish Hydro Electric Transmission in northern Scotland.
Used in: TEC tracker, Edition 3
Ofgem
The energy regulator for Great Britain. It approves code modifications and sets the network price controls.
Used in: Five controls on the connections queue · Ofgem’s data centre milestones may bite at 1MW · What a data centre actually buys from the grid · Why does CMP470 make sense? · Why does CMP470 make sense? (post)