Skanska, the engineering firm responsible for the structural steel work at the Transbay Transit Center, where two cracked beams were discovered last week, is also at the center of a storm involving the $2.3 billion BART extension to the South Bay.

Just this month it was reported that the opening of BART’s 10-mile extension from Fremont to new stations in Milpitas and San Jose could be delayed well into next year after it was discovered that workers had installed used or noncompliant communications equipment.

The electronic components, which control everything from public address systems to passenger information signs and fire alarms, need to be replaced.

The general contractor for the BART extension is a joint venture of Skanska-Shimmick-Herzog, although the $1.2 million worth of communications equipment was installed by a subcontractor.

A representative for Skanska referred us to the Valley Transportation Authority, which is overseeing construction of the BART extension.

Authority spokeswoman Bernice Alaniz, said determining how the mistake happened is “still under investigation, because there is a whole supply chain” involved.

In the meantime, subbing out the bad parts could push back the opening of the line from this year until the spring of 2019 or later.

San Francisco Chronicle columnists Phillip Matier and Andrew Ross appear Sundays, Mondays and Wednesdays. Matier can be seen on the KPIX-TV morning and evening news. He can also be heard on KCBS radio Monday through Friday at 7:50 a.m. and 5:50 p.m. Got a tip? Call 415-777-8815, or email matierandross@sfchronicle.com. Twitter: @matierandross