The Trans Bay Cable is a high-voltage direct current

High-voltage direct current

A high-voltage, direct current electric power transmission system uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses...

 underwater power line

Power Line

Power Line is an American political blog, providing news and commentary from a conservative point-of-view. It was originally written by three lawyers who attended Dartmouth College together: John H. Hinderaker, Scott W. Johnson, and Paul Mirengoff...

 between San Francisco, California

San Francisco, California

San Francisco , officially the City and County of San Francisco, is the financial, cultural, and transportation center of the San Francisco Bay Area, a region of 7.15 million people which includes San Jose and Oakland...

 and Pittsburg, California

Pittsburg, California

Pittsburg is a city located in eastern Contra Costa County, California, the outer portion of the East Bay region of the San Francisco Bay Area. The population was 63,264 at the 2010 census....

. The 53 mi (85.3 km) cable under San Francisco Bay

San Francisco Bay

San Francisco Bay is a shallow, productive estuary through which water draining from approximately forty percent of California, flowing in the Sacramento and San Joaquin rivers from the Sierra Nevada mountains, enters the Pacific Ocean...

 and through the Carquinez Strait

Carquinez Strait

The Carquinez Strait is a narrow tidal strait in northern California. It is part of the tidal estuary of the Sacramento and the San Joaquin rivers as they drain into the San Francisco Bay...

 can transmit 400 megawatts

Watt

The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...

 of power, enough to provide 40% of San Francisco's peak power needs. Owned by SteelRiver Transmission Company, the line connects PG&E's Potrero Substation to its 230 kV transmission line in Pittsburg. The system was completed in November, 2010.