What is TDR (Transmission Demand Residual)?

TDR (Transmission Demand Residual) explained | EnergyCode

Fixed daily charges for TNUoS introduced in April 2023, replacing the variable Triad-based system - your band (1-4) is determined by your Maximum Import Capacity (MIC) and voltage level.

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.

Current RIIO-2 Thresholds (April 2023 - March 2026):

Voltage	Band 1	Band 2	Band 3	Band 4
LV	≤80 kVA	81-150	151-231	>231
HV	≤422 kVA	423-1,000	1,001-1,800	>1,800
EHV	≤5,000 kVA	5,001-12,000	12,001-21,500	>21,500

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

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

Rates nearly double AND thresholds shift:

Voltage	Band 1	Band 2	Band 3	Band 4
LV	≤90 kVA	91-150	151-250	>250
HV	≤500 kVA	501-1,100	1,101-2,000	>2,000
EHV	≤3,500 kVA	3,501-11,000	11,001-20,000	>20,000

Critical Warning: EHV thresholds decrease in RIIO-3. An EHV site with 4,000 kVA capacity will automatically move from Band 1 to Band 2, potentially increasing TNUoS costs by 767%.

The MIC Optimization Opportunity:

Many businesses historically over-specified their MIC for headroom. Under TDR, this means paying more than necessary. If your actual maximum demand is well below your MIC, you may be able to review your demand data, request an MIC reduction from your DNO, and move to a lower TDR band.

Why April 2026 Matters: RIIO-3 rate increases are substantial. EHV sites between 3,500-5,000 kVA will automatically move up a band. Businesses should review their MIC now to plan reductions before the new period.

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