As used for electricity, the three half-hours of highest demand on the national electricity transmission system (NETS) between November and February each year, which form part of a charge-setting process designed to minimise energy consumption in peak periods. Triads must be at least 10 days apart to avoid all three potentially falling in consecutive hours on the same day, for example during a particularly cold spell of weather. For more information, see National Grid: TNUoS in 10 Minutes (January 2024).