BOSTON (WHDH) - Manhole covers have rocketed into the sky all over the state, in cities including Worcester, Somerville, and Boston’s Back Bay.
To understand how the heavy metal circles can get launched into the sky, 7NEWS was given an exclusive look below the street, tagging along with Eversource crews. 7 Investigates discovered chambers packed with the electrical wiring that power businesses, streetlights, and homes above.
“The cable has a conductor where all electricity runs through, and on top of that conductor is insolation that protects that cable from faulting,” said Bill Ritchie, Vice President of Electric Field Operations at Eversource.
Over time, weather and wear can break down that protection, and the lines can short out. When that happens, crews said the air in the space heats and expands, and pressure builds to a point where something has to give.
“If there’s no ventilation or egress for that air to go, it goes up,” said Ritchie.
Such explosions eventually sparked a solution.
Eversource invented new covers that diffuse the danger. They are designed with a lip that catches onto the ring of a manhole cover, keeping the lid in place.
The new cover made a difference on Northeastern University’s campus last year. Pressure building underground damaged the road and sent smoke pouring into the street, but the cover stayed in place.
Eversource crews are working to replace 33,000 manhole covers across the state.
Crews have already replaced all Eversource covers in downtown Boston. The company hopes to get the rest in place by the end of next year.
National Grid crews are also rolling out redesigned manhole covers to keep them locked down in high-traffic areas.
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