A fire on a bridge across the Teltow Canal in south-western Berlin could leave up to 45,000 households without power until January 8, grid company Stromnetz Berlin said on Saturday.
Local police said they are investigating the incident, which took place early in the day, as a possible arson attack.
The fire near the Lichterfelde heat and power station damaged several high-voltage cables.
"We expect a full restart of all customers by Thursday afternoon," the company said in a statement, noting it would require the installation of new cables.
It said some 2,200 commercial entities were also affected and mobile phone services and landlines might also be impacted.
Firefighters had been alerted at 0545 GMT and put out the fire, according to a police note posted on Twitter.
Criminal investigators and emergency services are on the scene, the police said.
