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Ever wonder how the cable cars in San Francisco climb those steep hills?

The heart of the cable car system is the Powerhouse located at the corner of Washington and Mason Streets. Each of the trolley lines—California Street, the Powel-Hyde, Powel-Mason, and their common section—all emanate from this terminal hub. Each line is independently powered by a 510HP (380 kW) DC electric motor and include speed-reducing gears and three large, self-adjusting pulleys called sheaves. The gears work to normalize the cable’s speed to 9.5MPH across all lines while the sheaves ensure the cables run through smoothly.

The cable itself is a 1.25-inch diameter steel rope comprised of six twisted strands, each of which are made of 19 individual wires encircling a sisal rope core. The cables vary in length from 9,300 feet on the Powell line to 21,700 feet for the California. Each cable is slathered with a tar-like substance that works much like axle grease, wearing and breaking down in the cable’s place. Even with this protective coating, the cables only last six to eight months on average. When one fails, the system is shut down that evening and a new cable is spliced into the feed.
via Gizmodo

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