Home / Glossary / What is TNUoS?Last reviewed July 2026

TNUoS

What is TNUoS?

Every unit of electricity your business uses travels down the motorway of the grid, the high-voltage transmission network of pylons and cables that carries power across the country, before it reaches your local wires. TNUoS is the charge that pays for that motorway. It stands for Transmission Network Use of System, and it is one of the bigger network costs bundled into your bill. How it is calculated changed significantly in 2022, and if your site is large the change may have shifted your costs. Here is what TNUoS is and how it works.

TNUoS is a network cost, not a supplier margin. It recovers the cost of the national transmission grid, it varies by where you are in the country, and a 2022 reform changed how the bulk of it is charged to businesses.

What TNUoS is

TNUoS, the Transmission Network Use of System charge, recovers the cost of building, maintaining and operating Great Britain’s high-voltage transmission network, the pylons and cables that carry electricity long distances from where it is generated to the regions where it is used. It is charged to both generators and electricity demand, and the demand share reaches you bundled into your business electricity rate.

Think of it as the toll for using the national grid’s motorway, before your power turns off onto the local distribution network for the final stretch to your meter.

What it pays for

TNUoS funds the transmission owners and the system operator for the infrastructure that moves power around the country: overhead lines, underground cables, substations and the ongoing investment needed to connect new generation and keep the network reliable. As Britain connects more offshore wind and reinforces the grid for net zero, transmission investment is rising, which feeds through into TNUoS over time.

How it is charged

The way TNUoS is charged to demand depends on your meter and size. Since the 2022 reform, most of the demand charge is recovered through fixed charges based on assigned bands, rather than purely on your peak-time consumption. Larger, half-hourly metered sites also face a locational element linked to demand at system peak. Smaller sites simply have it bundled into their unit rate.

The 2022 reform (TCR)

The Targeted Charging Review, or TCR, took effect on 1 April 2022 and changed how the main “residual” part of network charges, including TNUoS, is recovered. Instead of being tied to when you used electricity, the residual moved to fixed band charges. Every non-domestic site is assigned to a charging band based on its voltage connection and agreed capacity, and pays a set amount for that band regardless of exactly when it draws power.

The reform was designed to make network cost recovery fairer and harder to avoid. Its biggest practical effect was ending the old game of Triad avoidance.

Triads and why they mattered

Before the reform, the demand residual of TNUoS was based on your consumption during the Triads, the three half-hour periods of highest national demand between November and February, each at least ten days apart. A large site that cut its usage during those peaks could dramatically reduce its TNUoS bill, so “Triad avoidance” became a real strategy, often involving on-site generation or shutting down at forecast peak times.

Since TCR, the residual is a fixed band charge, so Triad avoidance no longer reduces it. A locational element linked to peak demand still applies to larger sites, but the sweeping savings some businesses once made from dodging the Triads have largely gone.

A worked example

Suppose your half-hourly site is assigned to a TNUoS demand band with a fixed charge of around £3,000 a year. Under the current arrangements you pay roughly:

£3,000 a year for that band, whenever you use your electricity.

Example only. Band charges vary by region, voltage and capacity and are reset annually, so treat this as illustrative rather than a quote.

The key contrast with the old system: before 2022, avoiding the three Triad half hours might have cut a bill like this substantially. Now the band charge stands whether you run at peak or not.

Why location matters

TNUoS has always been locational. The further you are from where power is generated, the more it costs to transport electricity to you, so demand in the south of England has historically carried higher transmission charges than demand in the north, where a lot of generation sits. Two identical businesses can face different TNUoS purely because of where they are. This locational signal remains part of the charge even after the TCR reform.

TNUoS on fixed vs flexible contracts

As with other network costs, how you see TNUoS depends on your contract:

For a larger site, understanding which model you are on matters, because TNUoS can be a meaningful share of a half-hourly bill.

How it shows up on your bill

On a fixed contract, TNUoS is invisible, folded into the unit rate with wholesale, BSUoS and policy costs. On a pass-through or half-hourly contract it is usually itemised among the non-commodity charges. If you want to understand how much of your rate is transmission cost, a bill validation can break it out. For a fuller treatment of the charge and how it is calculated, see our page on TNUoS charges explained.

What it means for your business

For most businesses TNUoS is a cost to understand rather than manage: it pays for the national grid, it depends partly on where you are, and since 2022 the bulk of it is a fixed band charge you cannot dodge by shifting usage. If you run a large half-hourly site that once relied on Triad avoidance, it is worth confirming how the reform changed your position. For everyone else, the practical step is making sure the network element of your business electricity rate is priced fairly, which a market review and a bill check will confirm.

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