06How electricity gets to your building

The short version: Electricity is made at power plants, pushed at very high voltage along transmission lines, stepped down at substations, carried through neighborhoods on distribution feeders, and stepped down once more by a transformer on a pole, on a pad or in a vault under the sidewalk. In New England a separate operator, ISO New England, runs the high-voltage grid while local utilities such as Eversource own the wires to your door. Dense downtowns, including Boston's, use underground "network" systems that keep the lights on when one cable fails. After years of little growth, demand is rising again in 2026, pushed by data centers and expected to climb further with heat pumps and electric cars.

How does electricity get from the power plant to my house?

Think of the grid as four layers, each run at a different voltage.

• Generation. Power plants, wind farms and solar arrays make the electricity. New England's grid has nearly 400 dispatchable generators - plants an operator can call on or turn down - with about 29,300 megawatts (MW) of capability.⁵⁶
• Transmission. Step-up transformers at or near the plant raise the voltage so it can travel long distances. ISO New England counts about 9,000 miles (14,500 km) of high-voltage transmission line, which it defines as 115 kilovolts (kV) and above.⁵⁶
• Substations. These fenced yards full of transformers and switches step the voltage down and split the power into local circuits called distribution feeders.
• Distribution. Feeders run along streets on poles or in buried conduit. A distribution transformer - the gray can on a pole, the green box on a concrete pad, or a unit in an underground vault - lowers the voltage again to what a building uses.

The reason for all this stepping up and down is efficiency: for the same amount of power, a higher voltage means a lower current, and lower current loses less energy as heat in the wire. High voltage is good for moving power across a state and bad for a toaster, so the grid changes voltage at each handoff.

In most regions, primary distribution feeders run at roughly 4 to 35 kV. In North America, common choices are 12.47 kV, 13.8 kV, 24.9 kV and 34.5 kV, while 4.16 kV is typical of older systems.¹⁵⁵

What reaches the outlet also differs by region. Most of the world receives 220 to 240 volts at 50 Hz; North America is the main exception, where most premises get a split-phase supply offering 120 or 240 volts at 60 Hz.¹⁵⁶ Europe adopted a harmonized 230/400-volt standard under a 1997 amendment.¹⁵⁶

What's on a utility pole?

An overhead distribution pole is a stack of separate systems, and the order on the pole tells you who owns what. One rural electric cooperative's guide lists the parts roughly from top to bottom:⁵³

• Primary line. The high-voltage distribution wire coming from the substation, at the top of the pole.
• Insulators. Ceramic or polymer pieces that hold the live wires off the pole.
• Fused cutout. A switch with a fuse that isolates a faulted transformer so one failure does not take down the whole line. When a crew "re-fuses" a transformer after a storm, this is usually what they are replacing.
• Transformer. Steps the voltage down for nearby buildings.
• Service wire. The line that runs from the pole to the building.
• Ground wire. Runs the length of the pole and ties into the neutral.
• Guy wire. The angled cable anchored in the ground that keeps the pole from leaning.
• Automated switchgear. Some poles carry automatic switches (one brand is the "IntelliRupter") that can reroute power around a fault.
• Telecom lines. Phone, cable and fiber, lowest on the pole and hung without insulators. These belong to the phone and cable companies, not the electric utility.⁵³ (More on those in 311, the wires under the street, and city data.)

The guide's order is approximate, and real poles vary: streetlight circuits, the neutral and secondary wires usually sit between the transformer and the telecom space. A useful rule for anyone on the street is that the higher the wire, the more dangerous it is, and anything on a pole should be treated as live.

Utilities inspect this equipment on a schedule. Eversource told the Boston City Council in late 2025 that a third party inspects its Boston poles every five years, that it checks switches every year, and that it flies infrared surveys yearly to spot equipment running hot.⁴⁶

Why are there no power poles downtown?

Walk through the Financial District in Boston or Midtown Manhattan and you will rarely, if ever, see a distribution pole. The wires are under the street, and they are usually arranged differently from the radial feeders in the suburbs.

A suburban street typically hangs off one feeder: if that feeder fails, everyone on it goes dark until a crew switches them to another. Downtowns often use a secondary network instead. Many transformers in underground vaults all feed one interconnected low-voltage grid, so a fault on one supply is isolated without interrupting customers on the others.⁷⁷ These networks are used "in downtown areas of cities where there are many customers in a small area."⁷⁷ A large building can have its own spot network: two or more transformers dedicated to that one customer.⁷⁷

The key part in the vault is the network protector, a switch that opens automatically when power would flow backward from the shared grid into a primary feeder that has gone dead.⁷⁷ Without it, a failed feeder would be fed from the wrong end, which would be dangerous for the crews sent to repair it.

Networks are very reliable and very expensive, which is why they are generally reserved for places where the density of customers - and the cost of an outage - justifies the cost.

Why do manhole covers explode?

Underground cable avoids ice storms and falling trees but brings its own hazard. When cable insulation breaks down, it can arc and set off fires, smoke and, occasionally, explosions inside manholes. Utilities call these manhole events.

New York's Con Edison has published detailed figures. It runs more than 94,000 miles (151,000 km) of underground cable, which NBC News described as the largest such system in the world, and some Manhattan cable predates 1930.⁸⁴ In 2014 it recorded 3,369 manhole events, of which 32 were explosions in which a dislodged cover caused injury or damage.⁸⁴ Sixty-eight percent of the events came in January and February, when most road salt goes down, and nearly 90% were caused by cable insulation breaking down.⁸⁴

Salty meltwater soaks into the vaults and attacks old cable. Con Ed's response has included vented manhole covers, which let gases escape before pressure builds.⁸⁴

Those figures are from 2015 reporting; current counts were not in our sources.

Who runs the power grid?

In much of North America the company that sends you a bill does not run the regional grid. An independent system operator (ISO) or regional transmission organization (RTO) dispatches power plants, manages the high-voltage system and runs the wholesale electricity market for a region, while local utilities own and maintain the distribution wires.

ISO New England is the operator for the New England region. It serves about 15.1 million people and 7.6 million retail customers.⁵⁶ Its job, minute by minute, is to keep supply matched to demand. That job is hardest at peak demand, the moment when use is highest. New England's all-time peak was 28,130 MW, set on August 2, 2006.⁵⁶

Peaks still bite. On June 24, 2025, between 5 and 6 p.m., with temperatures at 97°F (36°C), the region hit 26,586 MW, its highest peak in more than a decade.⁸⁵ Reserves - the spare capacity kept ready in case a plant trips - ran short for more than three hours. The lights stayed on, but the shortfall triggered about $97.1 million in "Pay-for-Performance" charges, the market's penalty and reward system for generators that do or do not deliver when called.⁸⁵

Other regions organize this differently, and outside North America many countries have a national transmission operator rather than regional ones.

In the US, FERC regulates six such organizations - PJM Interconnection, the Midcontinent ISO (MISO), the California ISO (CAISO), the Southwest Power Pool (SPP), the New York ISO (NYISO) and ISO New England - which together manage transmission for about 190 million people.¹⁵⁷ Texas has its own operator, ERCOT, whose markets FERC does not oversee, and parts of the West and Northwest sit outside any RTO.¹⁵⁷ In Great Britain, the National Energy System Operator (NESO), an independent public corporation, runs the electricity system for the whole country. On the continent, ENTSO-E is an association of 40 transmission system operators from 36 European countries.¹⁵⁸

Who gets power back first after a storm?

Restoration follows a published order, and it explains why your street may stay dark while the next one comes back. Eversource lists its priorities this way:⁴⁸

1. Public-safety and life-threatening calls, such as live wires down near people.
2. Blocked roads with electrical hazards, so emergency vehicles can get through.
3. Critical facilities: hospitals, police and fire stations, and water and sewage plants.
4. Transmission lines, substations and main feeders, prioritized by how many customers each one affects.
5. Distribution repairs that restore the most customers soonest, with single-customer fixes near the end.

The logic is upstream first. Fixing the wire to one house does nothing if the feeder behind it is still down, and fixing one substation can bring back thousands of customers at once. The person whose service drop was torn off by a branch is, unluckily, at the end of the list.

Should power lines be buried?

After every big storm, someone asks why the wires are not underground. Undergrounding does protect lines from wind, ice and falling limbs, and it removes poles from sidewalks. The objection is cost.

At a December 2025 Boston City Council hearing, Eversource cited a 2023 range of about $2 million to $6 million per mile (about $1.2 million to $3.7 million per km) for undergrounding, and said inflation and the tight conditions of a dense neighborhood such as Charlestown could push costs higher.⁴⁶ Verizon cited about $300 per linear foot for its conduit alone.⁴⁶ The hearing followed a July 29, 2025 incident in Charlestown.⁴⁶

Part of the expense is that every system on the pole - power, phone, cable, fiber, streetlights - has to move too, and each owner needs its own trench space or conduit. Underground faults are also harder to find than a broken wire you can see from the street.

In Boston

Boston's electricity comes from the New England grid run by ISO New England, and the local wires belong to Eversource. Downtown Boston and parts of Cambridge are served by underground distribution networks rather than overhead lines; the City Council asked Eversource to explain why at its December 2025 hearing.⁴⁶ Eversource does not appear to publish how many networks or vaults it runs in Boston, or exactly which neighborhoods they cover.

Most of the rest of the city, including neighborhoods such as Charlestown, still has poles. That hearing put a price on burying them ($2 million to $6 million per mile in 2023 dollars) and laid out Eversource's inspection schedule: poles every five years, switches yearly and annual infrared flights.⁴⁶ Eversource also told the council it is installing advanced metering infrastructure (smart meters) and a distribution management system, the latter required by Massachusetts regulators at the Department of Public Utilities (DPU).⁴⁶ Both give the utility a live view of where power is flowing and where it has stopped, instead of waiting for customers to call.

When a nor'easter knocks out power, Boston restoration follows the same Eversource priority list described above: safety calls and blocked roads, then hospitals and water and sewer plants, then the big lines, then the long tail of individual homes.⁴⁸

How it changed

The first electric street circuits were lighting systems. Paris lit the avenue de l'Opéra with electric arc lamps on May 30, 1878, and Cleveland demonstrated 12 electric lights around Public Square on April 29, 1879.¹⁵⁹ Arc lamps gave way to incandescent bulbs, often wired on high-voltage series circuits, late in the 19th century.¹⁵⁹ (The street lighting side of this story is in How streetlights work.)

Underground cable followed in the densest cities. Some of the cable still in service in Manhattan predates 1930, which helps explain why insulation failures are so common there.⁸⁴

New England's peak of 28,130 MW in August 2006 still stands as of October 2026.⁵⁶ With the record holding for two decades, the recent upturn in demand stands out. The data center share of that demand was still small: US data centers used 58 terawatt-hours (TWh) in 2014.¹⁶⁰

What's changing now (2026)

Demand is climbing again, and the reasons differ by place.

Data centers. Lawrence Berkeley National Laboratory estimated that US data centers used 176 TWh in 2023, or 4.4% of US electricity, three times their 2014 use, and projected 325 to 580 TWh, or 6.7% to 12%, by 2028.¹⁶⁰ That range is wide because nobody knows how fast AI computing will grow.

Batteries. Grid storage is the fastest-growing piece of new capacity. US utility-scale battery capacity was 43.6 gigawatts (GW) at the end of 2025. Developers added 8.3 GW in the first half of 2026, bringing it to nearly 52 GW, with 14 GW more planned for the second half of 2026 and 26 GW for 2027.¹⁶¹ Batteries charge when power is cheap and plentiful and discharge into the evening peak.

Rooftop solar. New England has about 400,000 distributed solar installations totaling about 7,500 MW, mostly behind the meter: on homes and businesses, where they reduce the demand the grid sees rather than showing up as a power plant.⁵⁶ This helps explain why the June 2025 peak came at 5 to 6 p.m. rather than mid-afternoon: as the sun drops, rooftop output falls while air conditioners are still running.

Heat pumps. ISO New England forecasts total electricity demand growing about 1.0% a year through 2035, but winter peak growing about 2.9% a year.⁵⁶ Our reading of those numbers: as buildings switch from oil and gas heat to electric heat pumps, the coldest night of the year, not the hottest afternoon, may become the moment the grid is built for. New England could become a winter-peaking grid sometime in the 2030s.

For a city, the tight spot is often not the power plant but the last mile. Every block that adds EV chargers or electrifies its heating may eventually need a bigger transformer, a reinforced feeder or a new substation, which is why utilities are investing in the meters and management systems that show them where load is growing.

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