A unit of energy measurement, often used alongside kWh. To calculate the equivalent value in kWh, multiply the number of therms by 29.3071.


A device used to adjust the voltage of an electric current. Transformers can be used to increase or decrease the voltage of an electrical power supply.


The transfer of a high-power electrical current from the UK’s power stations across the National Grid Company’s (NGC) nationwide grid system.

Transmission Use of System (TUoS)

These charges are incurred when transmitting electrical power across the National Grid network. The TUoS rate is calculated by applying a rate charge to the TRIAD demand level (see below).

Transportation Charge

The transportation charge is levied by the relevant Transporter and covers the cost of transporting gas through the relevant parts of the Gas Network. Transportation charges are calculated using three unique elements: capacity charge, commodity charge and site charge. 


The National Grid uses Triads to calculate TUoS charges. A Triad is calculated by using the three maximum demand points of an electrical supply at half hourly intervals, before calculating the average total. Triad periods occur at peak times during the winter months, when the demand for electricity is at its highest.