FARMINGTON (AP) – Vandals stealing valuable copper grounding wire cut power to as many as 2,100 customers for several hours overnight Thursday.

Maine’s two largest electric utilities have been hit by thieves who broke into substations.

The latest breaks were at Central Maine Power Co. substations in Farmington and Strong, disrupting service to as many as 2,100 customers.

Repair crews had to remotely cut electricity to de-energize the substation equipment before they could enter the fenced-in enclosures, CMP spokesman John Carroll said.

Thousands of dollars worth of wire was stolen earlier this month from four Bangor Hydro-Electric Co. substations in Chester, a burglary that triggered a brief shutdown of a power link to Canada and disrupted service to major customers.

Maine State Police are investigating those thefts, which were discovered May 12 during routine security checks.

One or more burglars broke locks at the substations and tampered with wiring that was being used as grounding, utility officials and state troopers said at a news conference Friday outside Bangor Hydro’s electrical operations office in Veazie.

“Such vandalism really compromised the safety of the power system,” said Rob Bennett, utility president and chief operating officer.

Although power was rerouted, two mills in the Lincoln area reduced their operations and a vital backup link that allows power to flow between New England and the Canadian Maritimes was shut off for eight hours while workers restored the system.

Bennett wouldn’t identify the affected mills, but Lincoln Paper & Tissue officials acknowledged that the mill cut its power consumption on short notice for about six hours May 12-13.

The mill operated with only one of its five machines while Bangor Hydro switched to another substation so the ones in Chester could be worked on, said Keith Van Scotter, mill president. He said the cost of the downtime was substantial.

State Trooper Thomas Fiske said investigators have taken evidence, interviewed suspects and are following up on leads. While he wouldn’t speculate on the reason for the theft, copper prices have more than doubled over the past year.

Officials cited the danger of electrocution, both to the burglars and those who worked to get the system back up.

“It put the vandals at extraordinary risk,” Bennett said. “Also it put our employees at risk, and it had a tremendous impact on the economy.”

He said the company was still assessing the costs of the vandalism and repairs.