question

The Lynx distribution system is basically positive and negative bus bars with added features built in. I havn't seen that particular schematic but my guess is the Lynx negative distribution bus has a heavy gauge negative cable connected to it. If it does and this cable is bigger than or equal to the size of the multiplus earth/case ground, you can terminate the case ground on the Lynx busbar. If its smaller then you would need to terminate the case ground at the point where it grounds to the chassis, engine or grounding plate (boats). If your BlueSeas negative DC busbar is fed by a 4/0 cable from the chassis ground point you can use your busbar as the ground point for your inverter case earth/ground.

The multiplus case ground serves two purposes. to bond neutral and earth when inverting (while disconnected from shore power) for proper functioning of GFCI type outlets and to carry a fault or short current if the DC positive wire ever shorted to the inverter case. at least this is how i understand it to work with Victrons inverter/chargers. depending on the size of your battery bank, this could be several hundred amps. this is why this earth/case wire needs to be so big. also, there can not be any smaller earth wires between it and the point where it exits the vehicles ground. if there is and several hundred amps are forced onto a smaller gauge wire, it will melt or possibly catch on fire. luckily for us a DC fault to case like this is exceptionally rare event, but scarry enough of a thought for sailors who might be in the middle of an ocean to wisely include this ground. a fire on the side of the road is unfortunate. a fire in the middle of an ocean would most likely be tragic.

Couple interesting links if your interested. Victron actually has some really good documentation on grounding but it seems so hard to find. It should be readily available on every product page on their website.

https://www.victronenergy.com/media/pg/The_Wiring_Unlimited_book/en/ground,-earth-and-electrical-safety.html#UUID-7790f868-512d-9080-00fb-c272426e66c5

https://www.youtube.com/watch?v=-X5wwPT5l-c&lc=Ugx02eakuv6VxFPX7Lh4AaABAg.A-5meo6-MK7A-85cPBhocB

I believe that the Multi's case is also connected to the AC PE connection so plan accordingly.