3D drawing of road bed, showing the cable conduit, as it was in San Francisco
1800s; in 21st century Dunedin an all-concrete format is the likely plan. Illustration from: The Cable Railways Company's System of Traction Railways for Cities and Towns. San Francisco, California, 1881.
A camera placed below street level, actually in the cable conduit, with the cable continuously running, on one of the San Francisco lines. Every now and then, a cable car arrives, with its grip mechanism sitting on either side of the cable. When the grip lever is pulled, the jaws of the grip come together, and clamp upon the sides of the cable. The sparks are due to the friction of the soft iron of the jaws as they grasp the steel of the cable; once the contact is complete and the car is running at cable-speed (15.3 km/hr), there is no more friction. Unsurprisingly, the soft iron needs frequent replacement. The style of the Mornington grip will probably be a little different, with the clamping imposed vertically on the cable; see the CAD picture further down.
Click photo for YouTube video of a view from within the conduit, as the cars release and grip the cable.
CAD drawings of Mornington car 103
(courtesy Lawrie Cooper, Tramway Historical Society, Ferrymead):
The central chassis of Car 103 under reconstruction with the Tramway Historical Society at Ferrymead. Note the ironwork in the middle, which will house the grip and brake mechanisms, and the axle attachments (no springs on these cars!) on the next beam.
Format of the cable winding apparatus, to be housed in the permanent Cable Car Building. From Watermusic in the Track. A History of San Francisco Cable Cars, Mike Phipps & Don Holmgren, publ. Friends of the Cable Car Museum, San Francisco, 2012. An alternative possibility would be a single large sheave (of diameter of the distance between the middle of the two tracks), similar to the arrangements in the gondolas and ski lifts of Central Otago.