A state appeals court ruled Thursday that Commonwealth Edison Co. owes more than 34,000 customers for damage caused by widespread power outages from a 2011 storm.

Under Illinois’ Public Utilities Act, power companies are subject to pay for damages — such as spoiled food or damage to property and vehicles — when 30,000 or more customers lose power for four or more hours.

But ComEd and the state disagreed whether the 30,000-customer threshold only counted from a single event in ComEd’s system or was an aggregate of all simultaneously affected customers systemwide.

In a 27-page opinion written by Justice James R. Epstein, the 1st District Appellate Court panel ruled that the language in the law is ambiguous enough that both parties’ interpretations were reasonable. But the court deferred to regulators’ interpretations in absence of clearer language.

“Unless and until the legislature chooses to rewrite the statute in the manner suggested by either side, we will not substitute our own construction for the reasonable interpretation adopted by the agency charged with the statute’s administration,” Epstein wrote.

The ruling affirmed a June 2013 ruling by the Illinois Commerce Commission that found ComEd was liable to reimburse customers for damages after seven storms between February and July 2011 affected power for more than 2 million customers.

To establish that ComEd was liable, the ICC found that each storm caused at least 30,000 customers to experience interrupted service during a four-hour period. But it also waived liability for claims from six of the storms, finding that those interruptions were caused by unpreventable weather-related damage.

The ICC found that the 34,559 customers and their local municipalities impacted by the July 11, 2011 storm were entitled to compensation.

ComEd contended that it was not liable because no single interruption affected 30,000 customers. It also argued that the outages were unpreventable and caused by weather conditions.

An administrative law judge rejected ComEd’s reading of the law and its alternative argument, finding that more than 25,000 customers on July 11, 2011, lost power due to trimmable tree branches that came into contact with lines.

On appeal, ComEd contended that the word “interruption” in the law refers to a single break in service. It argued that a fallen tree limb in Highland Park and a lightning strike 65 miles away in Rockford may have come from the same storm passing over northern Illinois, but the two could not reasonably be considered the same interruption under the law.

But that interpretation presumes the legislature used the industry meaning of “interruption,” rather than a layman’s understanding of the term, Epstein wrote.

The Illinois attorney general’s office and the ICC asserted that the statute focused on the customers’ experiences, not the industry’s, and that ComEd’s interpretation defies the rules of English grammar.

The panel went to dictionary definitions of “interruption” for guidance, but found mixed results that supported both sides’ views.

“The word ‘interruption’ means something different to a utility than it does to a customer,” Epstein wrote. “To the utility, an interruption is an event on a system that causes customers to lose their connection with the integrated grid. From the customer’s perspective, he is subjected to a power interruption when his service is in the state of being interrupted.”

Because courts give substantial weight and deference to regulators’ interpretations when statutes are ambiguous, Epstein wrote, the panel affirmed the ICC’s orders.

Justices Nathaniel Howse Jr. and Terrence J. Lavin concurred.

A ComEd spokesman declined to answer a question on how much the customer claims could cost the company.

ComEd was represented by Thomas S. O’Neill, its senior vice president and general counsel; Deborah E. Decker, assistant general counsel for parent company Exelon Corp.; John J. Hamill, Kathryn Hunt Muse and Daniel T. Fenske of Jenner & Block LLP; and E. Glenn Rippie, a partner at Rooney, Rippie & Ratnaswamy LLP.

In a written statement, ComEd said it is disappointed in the ruling and is evaluating its next possible steps.

“The statute was put in place to ensure that electric utilities are held accountable for system reliability while acknowledging that severe weather is beyond our control,” the statement says. “We believe the decision misinterprets the intent of the statute.”

The ICC was represented by its solicitor general, John P. Kelliher, and the state was represented by Assistant Attorney General Evan Siegel.

In a written statement, attorney general spokeswoman Natalie Bauer said that the office is pleased the court rejected ComEd’s attempt to avoid reimbursing customers for what the state deemed preventable power outages.

The case is Commonwealth Edison Company v. Illinois Commerce Commission, et al., 2014 IL App (1st) 132011.