Representative Jerrold Nadler, whose district includes parts of Brooklyn and Manhattan, denounced what he called a “total lack of urgency and concern” by the warden, Herman Quay, and jail management. Inmates who needed electrical power for sleep apnea machines were at risk of a stroke, Mr. Nadler noted.

When Mr. Nadler announced that contracted electricians had already left, and that power was unlikely to be restored over the weekend, the crowd grew angry.

The Federal Bureau of Prisons released a statement on Saturday night on behalf of the jail’s management, saying that a new electrical panel had been installed by an outside contractor that day and that the “facility is working to restore power as expeditiously as possible.” It expected work to be completed by Monday.

The statement continued: “Inmates have hot water for showers and hot water in the sinks in the cell. Essential personal hygiene items and medical services continue to be provided.”

On Friday night, a court order allowed the lead federal and public defender in the Brooklyn office, Deirdre von Dornum, to tour the jail for four hours. Because the electrical fire had knocked out the lights and outlets, inmates could not use computers to contact relatives or request prescription refills, including for psychiatric medications, she said.

As officials toured the prison on Saturday afternoon, the protesters outside, including many relatives of inmates there, marched around the jail chanting, “Where is the warden? Where is the heat?”

As a brass band played outside, inmates pounded on the narrow windows of their cells, in their own form of protest.