NEW YORK (AP) - A judge has ruled that the New York City Department of Correction violated its own regulations by involuntarily confining some inmates for up to 23 hours a day for their own protection.

Manhattan Supreme Court Judge Hon. Marcy Friedman says inmates housed in so-called "close custody" are subjected to "the most severe isolation" in the city's jail system.

Current regulations require that inmates in protective custody be let out of their cells at least 14 hours each day.

Former Commissioner Martin Horn imposed the 23-hour isolation policy in 2005 to safeguard vulnerable inmates. Research has shown that such isolation can be psychologically harmful.

The judge's ruling, released Friday, asks the department to voluntarily comply with its own regulations.

The department had no comment.

The city's Law Department says it is studying the decision.