An Oregon wildfire continued to threaten the AC Pacific Intertie, one of the backbones of the Western U.S. power grid, on Thursday, although the transmission system was operating near normal capacity, a spokesman for the line's operator said.

Bonneville Power Administration spokesman Bill Murlin told Reuters fire breaks were being built around the Cycan substation, while a relay station was also being threatened by the blaze.

The fire has also been causing arcing, where electricity makes lightning-like leaps through the thick smoke, endangering firefighters.

Murlin said that on Wednesday afternoon the blaze caused a 15 minute outage on two of the four lines that make up the transmission system, forcing the Portland, Oregon-based agency to shut 2,500 megawatts of generation.

The line is currently operating with a southbound capacity of about 3,200 MW. One of the four lines, which can carry about 1,000 MW, is located far from the blaze and has not been impacted, while the other three lines at times have all come under threat, Murlin said.

One megawatt is enough power for 1,000 homes.

Murlin noted that at one stage on Wednesday it looked as if the fire was moving away from the lines, but there were signs early Thursday that such hopes were premature.

BPA had provisionally scheduled for three of the four lines to be taken down late Wednesday and through Thursday to allow firefighters to tackle the blaze without the threat of live electrical wires.

That outage was canceled after discussions between BPA and the Oregon State Department of Natural Resources and has not been rescheduled.

"That is not going to happen the way things are looking now," Murlin said.