The use of an electric starter required heavier duty cables than previously required for lighting and accessories.
When fitting it again it dawned that this most dangerous of cables from a short circuit viewpoint had no circuit breaker or fuse, nor had any car I have ever seen.
Should the cable become detached or rub through its insulation currents of up to 1000 amps could be generated with catastrophic consequences.
Perhaps it is too difficult to fit a 400 amp fuse, which is about what is required. Though most batteries are fitted fairly close to the starter motor reducing the risk, racing cars can require the battery somewhere in the rear.
I am still looking into this as I have seen firsthand what happens when a large spanner was dropped across the terminals of a starter battery for a large V12 diesel generator: it glowed red hot instantly for a few seconds then the battery exploded. Fortunately, we all lived to tell the tale, but I have never seen a brown skinned mechanic with such a bleached complexion.
The best place for a circuit breaker is right at the earth terminal of the battery.