How a transmission cost overrun reaches your power bill

When a road costs more than budgeted, the money comes from consolidated revenue and appears in a budget paper.

Transmission does not work that way. A transmission network is a regulated asset: the business that owns it is allowed to earn a set amount of revenue, determined by the Australian Energy Regulator, and that revenue is recovered from customers through network charges.

So when a transmission project costs more, the operator does not absorb it and does not go to Treasury. It applies to the AER.

Here is the chain.

Step 1: the project is flagged as a contingent project

Contingent projects are major network infrastructure assets identified in advance in a network business's long-term investment plans, but not yet committed.

They sit outside the business's ordinary five-year revenue determination precisely because their timing and cost are uncertain. Flagging them early means there is a mechanism ready when they proceed.

Step 2: the business applies for revenue

When the project proceeds — or when its cost changes — the network business lodges a contingent project application. That application sets out the amount of revenue the business seeks to recover from its customers to deliver the project.

This is the point at which a cost increase becomes a public document — and the point at which it can be refused. Transgrid's bid to recover more than $1 billion of overspend on Project EnergyConnect was rejected by the AER in a preliminary position on 1 September 2026, after a six-month review, on the basis that the blowout was not unforeseeable.

Step 3: the AER decides

The AER assesses whether the costs are prudent and efficient, and determines how much revenue to allow. Consumer advocates participate, and they routinely argue for less.

The mechanism sits in clause 6A.8.2 of the National Electricity Rules, which permits an adjustment to the maximum allowed revenues under an existing revenue determination.

Approved revenue is then added to the network business's five-year revenue determination.

Step 4: it becomes a network tariff

Each year, electricity distribution businesses submit a pricing proposal to the AER, containing the network tariffs they propose to charge. Those tariffs recover:

• their own revenues
• transmission network charges
• the costs of jurisdictional schemes

The AER approves the tariffs.

Step 5: the retailer decides what you see

This is the step most people miss. Retailers ultimately determine how network tariffs are reflected in the retail prices offered to customers.

Network charges are an input to a retail price, not a line item passed through unchanged. So the relationship between an approved transmission cost and what appears on a bill is real, but indirect.

What it actually costs a household

The numbers are smaller per household than the headline project figures suggest, because they are spread across every customer and recovered over decades.

A useful worked example: the AER approved cost recovery for early works on the North West Transmission Developments in Tasmania. Those costs are reflected in customer bills from 2025-26, with an estimated increase of around $5 a year in residential electricity bills in Tasmania across 2025-26 to 2028-29.

That is early works on one project. The cumulative effect of a national transmission build-out — Infrastructure Australia projects utilities investment more than doubling to $36 billion over five years — is the thing to watch, not any single determination.

Business customers see it differently. Network charges fall unevenly across customer classes, and industrial users have faced substantially larger increases than residential customers in recent tariff decisions.

Why contractors should understand this

It is not an energy-sector curiosity. It changes how these clients behave on site.

Variations are slower to settle. A client recovering through regulated revenue cannot simply agree a variation and absorb it. It has to be defensible to a regulator, in public, against consumer advocates. That reduces appetite for scope growth and lengthens claim resolution.

Prudency is the test, not affordability. The AER asks whether costs were prudent and efficient — not whether the client can pay. A client that cannot demonstrate it managed the work well risks not recovering. That pushes rigour, documentation and process onto contractors.

Documentation matters more than usual. If your client will eventually have to justify the cost of your work to a regulator, the records you keep become part of its case.

And the money is real. Regulated recovery means the funding exists once approved. The risk is timing and quantum, not solvency.

Where else this applies

The same architecture, with different regulators, covers most Australian utility infrastructure:

• CopperString is to be delivered as a regulated asset, with a new regulated entity established for the Eastern Link
• Marinus Link equity allocations between three governments are expected to change once the AER determines the project's final cost, with Tasmanian customers carrying 27.6 per cent of annual costs and Victorians 72.4 per cent
• Water works the same way but state by state, with no national equivalent. The Alkimos Seawater Desalination Plant's A$2.8 billion is funded by user charges, reaching bills through a state economic regulator with far less scrutiny

What to watch

1. The AER determination on HumeLink, which sets the precedent for every transmission project behind it.
2. Annual network tariff decisions, where approved project costs actually surface.
3. Whether consumer advocates become a routine party to major project cost disputes.
4. State water pricing determinations, which carry desalination costs with a fraction of the attention.

Published 7 September 2026