Previously I wrote:
The ND alternators Ross, Blain, and Mickey have checked apparently do not have an internal stator-to-field connection. It appears the only source of field current is via the IG terminal. An OV device installed in the IG lead will shut them down if the regulator goes nuts for any reason.
I've since been doing some research, gathering information about ND units, and dismantling a spare Plane Power alternator. Right now I have a question in with the ND tech line, and learning continues.
At this time I'm pretty sure the above statement is wrong.
I do not yet have a schematic for the ND regulator's IC chip. However, after looking at the TDS for a few voltage regulator IC chips in the open marketplace, it seems likely that the Denso regulator's electronics are actually powered full-time (at very low current) via a tap to the B terminal's rectifier bridge, and the IG terminal is fundamentally an ON-OFF switch for the IC, not a field power supply. More research to come; God is in the details. For sure the typical ND has a very direct stator-to-field connection, with the regulator on the ground side of the field.
Greg is right; this thread was about a requirement for OV protection with an EarthX, not alternator control. Future posts regarding alternator control will go to the other thread.