TDR

The Transmission Demand Residual (TDR) is the main component of TNUoS charges since the Targeted Charging Review (April 2023). It replaced the old Triad-based system with fixed daily charges based on capacity bands.

How TDR Actually Works:

TDR uses 4 bands per voltage level, with band determined by your Maximum Import Capacity (MIC) agreed with your DNO. Band thresholds are set by NESO using percentiles (40th, 70th, 85th) of GB-wide capacity data.

RIIO-2 Thresholds (April 2023 - March 2026, superseded):

LV No MIC sites are banded by annual consumption (kWh) instead.

RIIO-3 Changes (April 2026 - March 2031):

Rates nearly double AND thresholds shift:

Critical Warning: EHV thresholds decreased in RIIO-3. An EHV site whose average agreed capacity over the allocation window (1 May 2022 to 30 April 2024) was 4,000 kVA moved from Band 1 to Band 2 automatically on 1 April 2026, an increase in TNUoS residual of up to 767.0%.

Reducing MIC does not move your band before 2031:

Many businesses over-specified their MIC for headroom, and under TDR that lands them in a higher band. DCUSA Schedule 32 ¶4.5 holds a Final Demand Site in its charging band for the duration of the price control period, so a RIIO-3 band stands until 31 March 2031 whatever happens to the MIC. A capacity reduction still cuts the DUoS capacity charge in proportion from the date the DNO registers it. It does not change the TDR band. The one mid-period route that turns on capacity, ¶6.1(b), needs a change of use or site configuration, a capacity change of more than 50.0% against the MIC held on 30 April 2024 (¶6.3(a)), and a signed letter from a company director (¶6.2).

Two dates that matter: your DNO takes the MIC snapshot for the RIIO-4 allocation in January 2029 (¶3.1), so a reduction registered before then sets the next band. And if the RIIO-3 allocation itself was wrong, a ¶7 dispute rebates up to six years (five in Scotland) from the first incorrect charge (¶7.17). A ¶6 request only rebates from the date the DNO received it (¶6.4).

What changed on 1 April 2026: RIIO-3 rates nearly doubled, and EHV sites averaging 3,500 to 5,000 kVA over the allocation window moved up a band. Those allocations hold to 31 March 2031.