First, I have seen several installations where the ammeter was
connected between the alternator/generator and the main bus. When
connected this way, only the total of charge plus load will be shown,
and never discharge. Connecting the ammeter between the battery and the
bus will show any charge going into the battery over and above the
load, and also discharge when the alternator/generator is not supplying
sufficient charge.
Second, and this applies only if you have a regulator separate from
your alternator/generator and you have a circuit breaker between the
alternator/generator and the bus. With the regulator connected to the
main bus, if the CB from the A/G to the bus were to open for some
reason, the regulator, sensing the lower bus voltage without the A/G
supplying charging voltage, will supply maximum current to the field.
With maximum field current and the high rpm at which we spin our A/G's,
its output could rise to 50V-150V depending on rpm and no load. If you
were to reset the A/G CB at this time, to could put a substantial
voltage/current transient on the bus, which could fry your electronics.
This transient could last for the regulator's filter time-constant and
the A/G field time constant, which could be many milliseconds. The
battery does not supply a good clamp on this transient due to its
internal resistance, along with the inductance of the battery to bus
leads. Electrically the way you can protect this from happening is to
connect the regulator's battery connection to the A/G side of the A/G
CB. In this way, even if the A/G CB opens, the regulator is still
connected to the A/G output and will maintain a regulated output. Of
course, the alternative is never reset the A/G CB with the engine
running!