The boardwalk fire in Seaside Park and Seaside Heights began accidentally Thursday in aged wiring that had been compromised by saltwater and sand during the Oct. 29 storm, federal and county investigators said at a news conference.
The wind-whipped blaze destroyed more than 50 businesses in the two towns.
Ocean County Prosecutor Joseph Coronato said the fire should be a cautionary tale.
"I'm sure on every boardwalk everywhere (at the Jersey shore), there may be compromised wiring," he said. "We don't want to start a panic mode; we just want to be reasonable. If you're a property owner and you think your electrical work came in contact with water and sand, we strongly recommend you have it inspected."
Seaside Heights officials did not immediately return a message seeking comment about the status of wiring in the surviving two-thirds of the boardwalk.
Investigators said the fire began in wiring that dated to the 1970s, and was located under a Kohr's frozen custard stand and the Biscayne Candies shop last Thursday afternoon.
Jessica Gotthold, a senior special agent with the Bureau of Alcohol, Tobacco, Firearms and Explosives, said investigators located wires under the boardwalk that somehow came in contact with each other, causing an electrical arc that is believed to have started the fire.
Coronato said those wires had been exposed to the storm surge and grating sand action of the storm, which compromised them.
But as far as why the wires contacted each other, he said, "we will never know."
The prosecutor said the investigation ruled out all other possible causes of the fire, including careless smoking or a deliberate act of arson. The wiring was inaccessible to the public, he noted.
Authorities even pulled financial records of the businesses involved in the fire to make sure no one had a financial motive to start a fire.