PHILADELPHIA (AP)  A federal appeals court has overturned a rule that said a cable TV company could not serve more than 30 percent of the nation’s subscribers. The decision, released Friday, was a victory for the largest cable company, the Comcast Corporation, which has a 25 percent share and sued to block the rule.

It was an embarrassing decision for the Federal Communications Commission, which had reimposed the cap after it was rejected twice before. Friday’s ruling from the United States Court of Appeals for the District of Columbia Circuit called the limit “arbitrary and capricious,” and threw it out.

Fearing a cable monopoly, Congress directed the F.C.C. in 1992 to set limits on how many customers cable TV operators could reach nationwide. The agency set the limit at 30 percent, but that was thrown out twice by the courts. Two years ago, under chairman Kevin J. Martin, the same cap was reinstated, prompting the new challenge from Comcast.

In the ruling, the appeals court noted that the F.C.C. sought to justify the previously rejected cap by recalculating its formula. But the outcome remained the same at 30 percent.