Inverter/Charger grounding question

[fireman_bob]

Hi, I've got a 2003 Sea Ray sedan bridge 480 I'm working on. I'm putting in an inverter/charger using the 24VDC bow thruster batteries. In the electrical diagram for this boat, it shows the bow thruster motor case and 24v battery B- connected to the grounding bus (green wires), yet I don't see any physical connection nor do I get any continuity from 24v B- to the grounding bus. The bow thruster motor case is connected to 24v B- wire at the motor ( I don't think this meets ABYC requirement?).
I believe the ABYC requirements for inverters specifies the unit's chassis ground needs to be connected to the "engine negative terminal" (grounding bus) and not just the DC B- point which is the 24v battery in this case. Would there be any issue connecting the 24v B- to the grounding bus to meet this requirement? Or can I just connect the inverter chassis ground to the B- connection (without having the B- connected to the grounding bus)? The problem I see with the latter is that if a short from AC line to case developed, it would energize the 24v B- bus and not take out the upstream AC breaker.

 

[Grandad]

Hi Bob. I don?t know whether this will be much help, but after searching for bow thruster schematics for the 480, I also found a similar schematic for the 390. One of the differences in the drawings helped me to determine that the box shown for the bow thruster is actually the motor of the bow thruster, not the case. The 390 schematic specifies a #2 AWG ground jumper from the motor to the case, whereas the 480 does not. I?m thinking that this may simply be an omission on the 480?s schematic. - Grandad
View attachment 480 Bow Thruster Schematic.pdf View attachment 390 Bow Thruster Schematic.pdf