Jul 23, 2025
Connecticut Project Highlights Trade-Offs in Underground Transmission
It is easy to justify underground transmission projects when your baseline is repairing the damage caused by powerful storms. And although underground transmission is likely to be the trend moving forward, there is a give and take involved. A project now unfolding in Connecticut exemplifies this perfectly.
The project, designed to update aging infrastructure and keep a local railway operating at current service levels, is being completed in five phases. Three phases have already been completed while the fourth is currently in process. Meanwhile, the fifth phase is stuck in limbo. An estimated $838 million price tag is forcing decision makers to rethink the route's underground design.
More Than Twice the Cost
Improving the infrastructure between Fairfield and Congress would cost United Illuminating and the Independent System Operator of New England (IS-ONE) an estimated $306 million if completed using overhead transmission lines. But the cost of underground transmission is more than double.
As for how the project would be paid for, it depends on the option they go with. If they choose above ground transmission, the entire cost would be borne by the 14 million customers within IS-ONE's operational region. If the underground transmission plan is adopted, the first $306 million would still be borne by those 14 million customers. But the remaining $532 million would be borne exclusively by Connecticut ratepayers.
United Illuminating is not sure they could convince state regulators to allow them to pass on such a huge amount. And of course, rate payers probably wouldn't be happy with their increases. The utility says it really doesn't want to go with underground transmission for this final leg because of the commitment they have made to customers, the commitment to find the least expensive means of achieving stable and reliable power.
The Give and Take
Time will ultimately tell how the Connecticut project is finished. But what is currently happening in the state illustrates the give and take nature of underground transmission. On paper, underground transmission seems like a great idea. Bury power lines underground and they are not subject to severe storms that can damage infrastructure to the tune of tens of millions of dollars. On the other hand, installing underground transmission lines is incredibly expensive.
For some in the industry, it is a 'pay me now, or pay me later' scenario. The idea is that underground transmission pays for itself in the long term by reducing repair and maintenance costs. But there are others who disagree. They say underground transmission never fully pays for itself because it has its own maintenance issues.
Each Project Is Different
Another thing the Connecticut project reveals is that each project is different. How often does Connecticut suffer tens of millions of dollars in weather-related damage to its regional grid? Probably not as frequently as states that routinely deal with tornadoes and hurricanes.
Given the number of times some Florida utilities have had to rebuild the grid over the last decade, investing in underground transmission makes sense. But does it make sense in Connecticut? Regulators, utilities, and consumers will ultimately have to decide for themselves.
Underground Transmission Is the Future
Regardless of how things play out in Connecticut, underground transmission is the future. A day will come when overhead transmission lines are obsolete. It is simply a matter of how long it takes to get there and what the final bill will be.
Underground transmission ultimately has benefits that simply cannot be replicated with overhead systems. They are worth investing in. And as more projects are built, the move toward underground transmission will gain momentum.
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