The Trans Bay Cable is a high-voltage direct current underwater cable interconnection between San Francisco, California and Pittsburg, California. The 53 mi (85 km) cable under San Francisco Bay and through the Carquinez Strait can transmit 400 megawatts of power at a DC voltage of ±200 kV, enough to provide 40% of San Francisco's peak power needs. The line connects PG&E's Potrero Substation to its 230 kV transmission line in Pittsburg. The system was completed in November, 2010. The Trans Bay Cable Project was the first commercially operated HVDC system to use the Siemens HVDCPlus Modular Multi-Level Converter (MMC) VSC system.
Trans Bay Cable is operated by a dedicated team of operations, engineering, and maintenance staff, on a 24hr a day basis, and is a Participating Transmission Operator on the California ISO Grid.