It could take 10 years to fully upgrade downtown Honolulu’s underground electric cable network under a plan being accelerated after two disruptive outages over the past two weeks.

Representatives of Hawaiian Electric said the utility company had begun downtown cable replacement work during the prior decade and completed about 25% of the project before the coronavirus pandemic interrupted the effort.

Now, the remaining 75% has become more of a pressing need after three recent outages downtown, and strategies are being examined to do all the work on an accelerated timetable that the company estimates could take the next 10 years or perhaps less.

Much of the work will be challenging because of the confined spaces involved and other logistics.

The system, which includes equipment in underground vaults beneath streets and accessed by maintenance holes, was developed between the 1950s and 1960s, making it between 55 and 75 years old.

Another difficulty with replacing the cables that serve many office towers, residential towers, courthouses, the state Capitol and numerous small businesses, including many in Chinatown, is that some of the work has to involve cutting power to customers.

“Because it’s so old and the way it’s designed, we have to de-energize customers in order to do certain upgrades,” said Shelee Kimura, company president and CEO. “A lot of the work that has yet to be done is going to require us to take some customers down in order to do the replacements.”

Some of this work is anticipated to be done at night to minimize disruptions that can’t totally be avoided.

The utility company, which is regulated by the state Public Utilities Commission and serves Oahu, Maui, Molokai, Lanai and Hawaii island, continually weighs costs and benefits to determine system upgrade priorities. And given the unexpected series of recent outages downtown that were spread over six days for different customers, a plan to finish replacing cables in the area has been elevated.

“It’s better to have those planned outages than the unplanned outages,” Kimura said.

The recent trouble downtown began at night on June 12 when an outage between Mililani and Bishop streets damaged an underground cable feeding power into the downtown area, according to Hawaiian Electric.

The next morning, on June 13, equipment at the utility’s nearby Iwilei substation got overloaded and triggered a new power outage that affected about 900 downtown customer accounts and lasted about 10 hours. In many cases, a single account represented an entire building with hundreds of office or residential tenants.

Four days later, at night on June 17, another outage occurred after a fire in the underground system damaged cables in several locations. This outage was concentrated in the Chinatown area, and according to Hawaiian Electric did not include as big an area as the June 13 outage that affected most office buildings. But the Chinatown outage affected more customer accounts, about 3,000.

The fire damaged four underground circuits comprising 12 high-voltage cables spanning three blocks along King Street between Bethel and Alakea streets, according to the utility.

Hawaiian Electric was able to restore power to roughly 2,400 of the 3,000 affected accounts a day later, on June 18, after what the company described as painstaking work that included identifying and replacing damaged wiring as well as repairing ducts carrying conduits that had melted.

As repair work continued into the evening of June 19, an arc flash disrupted progress and forced Hawaiian Electric to shut off power to about 3,000 Chinatown customers.

The National Fire Protection Association has described an arc flash as a burst of electrical energy three times hotter than the surface of the sun accompanied by a pressure wave on par with a grenade blast.

Hawaiian Electric said four technicians were inside a maintenance hole in the vicinity at the time of the arc flash but were not hurt.

Finally, on June 20 power was restored to about 2,400 customers at about 8 a.m., followed by the remainder of affected customers at about 3:45 p.m.

Company officials have said they believe some kind of electrical failure in the downtown system led to the June 17 fire, which then caused collateral damage.

Kimura said an analysis to determine a root cause of the outage is ongoing and could take a month to complete.

Meanwhile, customers can file claims with Hawaiian Electric in an effort to receive compensation for losses or damage resulting from the power outages. There are no parameters for what can be in a claim, though coverage is determined on a case-by-case basis. Claims must be filed within 30 days of an outage. More information about filing claims is available at 808ne.ws/hecoclaim.

As of early Wednesday, the company said 42 claims had been filed over the June 13 outage and 102 had been filed over the outage that began June 17.