* Pipelines shut down for five to seven hours
* U.S. govt looks at how to boost pipeline security
* Activists face charges after tampering with lines (Updates with background on protester arrests, adds background, quotes from regulator and TransCanada executive)
By Catherine Ngai and Nia Williams
NEW YORK/CALGARY, Oct 12 (Reuters) - Five oil pipelines disrupted by environmental protesters were back up and running on Wednesday after an unprecedented act of sabotage left policy makers and energy executives from Calgary to Washington mulling how to secure key energy infrastructure.
Protesters simultaneously broke into valve stations at five different remote locations on Tuesday to stop the flow of crude through arteries that carry millions of barrels of crude from Canada to the United States every day.
Companies operating the pipelines, which pump around 15 percent of U.S. oil consumption, shut down their lines for between five and seven hours as a safety measure before the restart, according to Reuters estimates and company representatives.
The action on Tuesday underscored the vulnerability of the thousands of miles of pipeline in the United States that deliver energy to consumers.
In Washington, White House spokesman Josh Earnest said on Wednesday the departments of Homeland Security and Transportation were "trying to get to the bottom of what exactly happened and what potential steps could be taken to ensure the safety and security of our energy infrastructure."
"We certainly take that security quite seriously," Earnest told a daily news briefing.
Protest group Climate Direct Action said on Tuesday the action was to support the Standing Rock Sioux Tribe, which is protesting construction of the $3.7 billion Dakota Access pipeline, carrying oil from North Dakota to the U.S. Gulf Coast.
Activists across Montana, Minnesota, North Dakota and Washington state were arrested on Tuesday after the early-morning raids, which they posted on social media.
Part of that group included a documentary filmmaker, who was arrested and had her footage confiscated. She remained in custody in Pembina County, North Dakota, on Wednesday.
In Washington state, three protesters are in custody and are expected to face formal charges by Thursday evening, said Chris Baldwin, a sergeant with Skagit County Sheriff's office.
In Minnesota, two people have been charged in connection with pipeline tampering, said Rick Mollin, the county attorney for the Clearwater County Attorney's office.
TransCanada Corp's Keystone pipeline, Spectra Energy Partners LP's Express pipeline and Enbridge Inc's Line 4 and 67 all restarted Tuesday afternoon, according to company representatives.
Information provider Genscape said Keystone was running at reduced rates.
Kinder Morgan Inc said it was not operating a spur of the pipeline affected by the protesters, although it has since restarted the main pipeline.
Together, the pipelines can carry nearly 2.8 million barrels a day of crude across the border.
In Texas on Wednesday, a gathering of around 150 activists organized by the Texas Environmental Justice Advocacy Services held a protest in front of the offices of Energy Transfer Partners, spearheading construction of Dakota Access.
Reporting by Catherine Ngai in New York and Nia Williams in Calgary; additional reporting by Rory Carroll in San Francisco, Jeff Mason in Washington, DC and; Editing by Simon Webb and James Dalgleish