THE POWERHOUSE

Each of the different cable car lines once had its own powerhouse —or sometimes several—to drive the cable used on the line. The first power sources were steam engines powered by enormous amounts of coal each day, thus each powerhouse was equipped with boilers to heat the water needed to produce steam. During the decade after the 1906 quake, steam power was replaced by electricity. Before the 1982 restoration, a single 750 horsepower electric motor drove all the three remaining cable lines, with another identical motor for backup.

After restoration, four 510 horsepower engines were installed, one for each cable with its own separate gearbox. A set of six 14-foot diameter sheaves is driven by the motors, around which the cable runs in a figure-eight pattern to reduce slippage. Tension sheaves keep a constant tension on the cable and takes up slack produced by wear, car load and stoppage of cars on the line.

From the tension sheave the cable moves back under the power sheaves into an enclosed channel through which it passes out of the powerhouse and under the street to the tracks.



The
Powerhouse