Five Star Customer Service
Stress Free Switching
Utility Management
Competitive Prices
What TNUoS Charges Are
TNUoS charges fund the maintenance and operation of Britain’s high-voltage transmission network. Think of it as the motorway system for electricity. Your local network (the “A-roads” and smaller roads) is covered by DUoS charges, but the main transmission backbone that moves power from power stations and renewable sources across the country is what TNUoS covers.
These charges are set by National Grid ESO (Electricity System Operator) and are mandatory for all businesses connected to the network. You can’t avoid them or negotiate them individually. They’re standardised based on where your business is located and how much power you use.
The reason businesses have to pay separately for transmission is practical: the network costs money to build, maintain, and upgrade. Using a “cost-reflective” model means businesses that use more power (especially during peak times) pay proportionally more of these costs. This encourages businesses to spread their usage more evenly and invest in efficiency.
TNUoS vs DUoS
It’s easy to confuse these two charges because they sound similar and both appear on your bill. Here’s the key difference:
TNUoS = Transmission Network Use of System (high-voltage, long-distance network)
DUoS = Distribution Network Use of System (local distribution network)
Think of National Grid ESO as owning the motorways, while local distribution network operators (DNOs) own the A-roads and local roads. Both sets of infrastructure need paying for, so both charges exist.
In cost terms, DUoS is usually the larger charge for most businesses because the local network is denser and more expensive to maintain. TNUoS tends to be smaller, but it varies by region and your consumption profile. Some regions have higher TNUoS charges than others because transmission is denser there or more investment has been needed.
Your electricity supplier includes both charges in your final bill, but they’re calculated separately and go to different organisations. National Grid ESO collects TNUoS, while your local DNO collects DUoS.
How TNUoS Is Calculated
TNUoS is worked out using two main methods depending on your usage profile: demand tariffs and Triad charges.
Demand Tariff Charges
Most businesses pay TNUoS through demand tariffs. These vary by region and are based on your peak demand during specific times. National Grid divides Great Britain into 14 demand tariff zones, each with different charge rates.
Your zone depends on where your business is physically located. A business in London sits in a different zone from one in Glasgow, and the TNUoS charge per kW reflects the transmission congestion and costs in that area.
Within your zone, you’re charged per kilowatt (kW) of your peak demand. The supplier measures your usage over half-hour periods throughout the year and charges you based on your maximum demand during certain periods (usually winter months, which is when the network is most strained).
Triad Charges
If you’re a larger business with significant consumption, you’ll face additional Triad charges. These are based on your consumption during the three highest demand half-hours that occur across winter (November to February). Even if you only use high power for short periods, hitting a Triad window can add thousands to your bill.
Triad Charges
Triad charges deserve their own section because they’re the part of TNUoS that causes the most confusion and often the biggest costs.
How Triads Work
During winter, National Grid identifies the three half-hour periods when the entire network is under the most stress. These are the Triad periods, and your business pays per kilowatt for whatever you consumed during those three windows, even if you only hit them once by accident.
Here’s a practical example: if your business has a peak demand of 150kW during normal times but surges to 300kW during an afternoon in January, and that afternoon happens to be a Triad, you’re charged for 300kW across all three Triad rates. One moment of high usage can double your TNUoS bill.
Triads are unpredictable. National Grid doesn’t announce them in advance. They typically occur on cold, dark weekdays (around 4-6pm) when heating and lighting demands peak. But a business can’t predict which days these’ll be.
Are Triads Being Phased Out?
Yes, slowly. The Targeted Charging Review (TCR) from Ofgem introduced changes to make TNUoS charges fairer for different business types. These changes are being rolled out gradually, but they’re moving away from Triad-based charging for smaller businesses.
Businesses with half-hourly meters will eventually move to a fixed charge based on their location and connection type rather than their actual consumption during Triad periods. Larger businesses with significant imports will continue paying Triads for a longer period, but even this is being reformed.
The transition isn’t complete, so check with your supplier about which model applies to your business. If you’re currently on Triads, there’s a possibility you could move away from them, which could significantly reduce your bill volatility.
What TNUoS Costs
Actual TNUoS charges vary widely depending on your region, business type, and consumption patterns.
Regional Variation
Some zones are much more expensive than others. London and the South East typically have higher TNUoS charges because that’s where demand is greatest and the network is most congested. Rural areas or less densely populated regions usually have lower charges.
A business in London might pay £20-30 per kW per year for the demand charge alone. The same business in Scotland or the Midlands might pay £10-15 per kW per year. That’s a significant difference when multiplied across your peak demand.
Triad Costs
Triad charges are billed per kW and per Triad. If your business consumed 200kW during each of the three Triad periods and the rate is £2 per kW, you’d be charged 200 x 3 x £2 = £1,200 just for Triads. For businesses with high or unpredictable peaks, this can be the largest component of their transmission charges.
A typical mid-sized manufacturing business might see TNUoS costs between £2,000-8,000 per year depending on zone and profile. Larger businesses could easily see five or six figures.
Reducing Triad Exposure
If you’re paying Triad charges, the most direct way to reduce costs is to avoid peaks during those three winter periods. Some businesses do this by shifting energy-intensive processes to other times, pre-cooling or pre-heating facilities before Triad windows, using onsite generation or battery storage to reduce grid imports, or working with their energy supplier to understand when Triads typically occur.
These strategies aren’t always practical, but even small reductions in your peak during Triad periods can save thousands.
How TNUoS Appears on Your Bill
When you look at your business electricity bill, TNUoS should be shown separately from the energy charge, DUoS, and other levies.
You’ll typically see Transmission Network Charge or TNUoS as a line item, the charge per unit (pence per kWh) or per kW depending on your tariff structure, a separate breakdown for demand charges and any Triad charges, and the total amount you’re being charged for that billing period.
Some suppliers break this down more clearly than others. If your bill doesn’t clearly show TNUoS, ask your supplier for a detailed breakdown. You need to understand what you’re paying for to identify cost-saving opportunities.
If you’re moving onto a new contract, make sure you understand whether you’re being charged via demand tariffs, Triads, or a newer fixed TNUoS model. The difference can be significant.
Key Takeaways
✓ TNUoS charges fund the high-voltage transmission network that carries electricity across Great Britain, and every business pays them as part of their connection.
✓ They’re set by National Grid ESO and vary by region, with some areas (like London) having significantly higher rates than others.
✓ Triad charges add extra costs if you hit high consumption during winter peak hours, and they’re impossible to predict in advance.
✓ The Targeted Charging Review is gradually moving businesses away from Triads, but the transition isn’t complete yet. Check your tariff to see which model you’re on.
✓ Understanding your charges helps you find savings. If you’re paying Triads, reducing peak demand during winter months can deliver real cost reductions.
✓ These charges are non-negotiable, but your energy contract and how you manage your consumption absolutely are.
▬▬▬
“Adam was very helpful and not at all pushy! Which was appreciated. My current water supplier was going to auto renew at double the price! Adam very successfully renegotiated a much more competitive price and has locked it in for three years.”
Nick, energy customer · ★★★★★ on Trustpilot
Clearsight Energy helps UK businesses compare, understand, and move to better energy contracts.
Compare business energy prices