The cable pull: a major milestone in upgrading BART’s electrical infrastructure
Story by MELISSA JORDAN | Photos by MARIA J. AVILA
BART Communications
Workers buzzed in a hive of activity last Friday night in the tunnel underground the 16th St./Mission BART Station as crews reached a major milestone in an important infrastructure improvement: large-scale installation of modern and robust high-voltage cables to reliably run trains.
When it’s all done, BART riders can expect a more resilient electrical power system to handle more frequent trains and support the growing number of Fleet of the Future trains.
The operation involved pulling three large cables through a conduit using a mechanical cable puller, part of an upgrade funded by the Measure RR bond that voters approved in 2016. The existing electrical system is from when BART was built in the 1960s.
Cable rail truck with 3,000 feet of cable being transported
The first task in a cable replacement project is to install new 6-inch phenolic (a thermosetting resin) conduits. These conduits are attached to the ceiling of the tunnels using high grade structural steel plates and clamps.
Crew setting cable and steel braided line in pulling guide
BART is using a new type of conduit that is lightweight, strong and durable. Benefits to these new types of conduit include less time to install, lower maintenance cost and longer service life. The second task is to insert a steel braided line into the entire length of conduit, ensuring the conduit is clear of obstructions and ready for the cable pull.
As soon as the steel braided line is pulled through the entire conduit, one end is attached to the electrical cables and the other end is connected to the mechanical cable puller.
A journeyman electrician attaches cable pulling guides to the steel ring of the tunnel using high-strength structural steel.
Now the cable pulling operation can begin. The seafoam green mechanical cable puller slowly pulls the cable into the lubricated conduit. It measures pulling tension every second to ensure no damage to the cable or conduit. It takes about one hour for the cable to travel through the entire length of the conduit. As the cable snaked along, workers listened for the sounds of its progress through the conduit.
An electrician attaching the steel braided line to the start of the cable pull
Once the cable reaches the mechanical cable puller end, all the cable is inside the conduit and the cable pull is accomplished. It may sound simple, but the workers face challenging conditions in the dark, cramped underground space. Large fans blow fresh air – required for workers to safely breathe -- into the tunnel.
BART’s infrastructure and system upgrades is considered essential work and thus can continue under the coronavirus shelter-in-place orders. Workers are equipped with face masks, safety glasses, hard hats and other PPE, and keep the greatest social distance possible on each job.
Managers watching work on cable pull operation
The additional time made available by BART’s 9 pm early closure, due to low ridership during the pandemic and in effect until further notice, is being used to ramp up projects like the electrical system upgrade.
Customers may be affected by the need to single-track for this project; the extra time is necessary to bring in staff and materials to be ready to go when trains stop running. This time means, potentially, we will be able to perform three cable pulls instead of one per shift. That equals up to 9,200 linear feet (or nearly 2 miles) of cable that can be installed each night. This could shave off many months of work affecting our customers from the five-year-long project
DMZ Builders, a local general engineering contractor based in Concord, is the contractor for the project.