Charges made by the system operator (see System operator (SO)) for the use of the National electricity transmission system (NETS) designed to cover the cost of installing and maintaining transmission system infrastructure. The tariff is set as £/kW and is calculated ahead of time. The charges may be positive or negative, depending on location, and their recovery is split between electricity suppliers and generators. Charges to generators are based on their transmission entry capacity (TEC). Charges to electricity suppliers and large industrial customers are based on their electricity demand at peak times. The obligation to pay TNUoS charges and the methodology for their calculation is set out in the Connection and Use of System Code (CUSC).

For more information on CUSC, see Practice note, Finding and using the industry documents: electricity and downstream gas.

For more information on TNUoS charges, and the reforms to these charges, see Practice note, Power purchase agreement: key issues for drafting, reviewing and negotiating: Embedded benefits, National Grid: Transmission Network Use of System (TNUoS) Charges and National Grid: TNUoS in 10 Minutes (January 2024).