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Charging policy and guidance

The methodology we use to set TNUoS tariffs and charges is in the Connection and Use of System Code (CUSC), Section 14, Part 2. The general methodology for TNUoS is in CUSC Sections 3 and 13.  On this page, you will find more about consultations, policy decisions, guides, and Triads data. 

Open letter consultations and guidance

These documents are open letters and informal consultations relating to TNUoS charging methodology as codified in the CUSC.

Charging methodology policy decisions

These are policy decisions documents relating to TNUoS charging methodology that are not codified within the CUSC.

Industry information guides

The following documents are designed to give you a better understanding of electricity generation charges and related topics.


Triads are the three half-hour settlement periods with highest system demand and are used by National Grid to determine charges for demand customers with half-hour metering and payments to licence-exempt distributed generation.  They can occur in any half-hour on any day between November to February inclusive but are separated from each other by at least ten full days. Triads are determined after the event using Elexon settlement metering data from November to February. This data is usually available around 24 March after which National Grid will confirm the Triad half-hours.  Once confirmed they are not updated for subsequent settlement data.  Indicative Triads based on data received to date can be found on Elexon's Electricity Data Summary.