Question.

Explain why the alternator output from phases are fed to separate bus bar.

The alternator output from phases are fed to bus bar. Individual alternator output is fed to its bus bar, which are then connected through isolating device connected to main bus bar.

If the alternator output was to be fed to a common bus bar, the phase would get shorted.

The phase sequence on main bus bar could change which would affect the machineries drawing current from the main bus bar.

For purpose of safety

For individual isolation of machine, if work has to be carried out.