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rubicon asked

MultiPlus 3K 12v ground

I’m in the middle of planning a new lithium system on my Winnebago Travato. I currently have 2 AGM batteries with a small 1K inverter. The new system will have (3) 100amp Battle Born batteries with a 3K MultiPlus inverter. I plan on running the current AC wire from an ATS (shore power and generator) to the AC input of the inverter as a pass through. The inverter AC output to the existing electrical panel that powers the system. I’m replacing the OEM DC battery cable with 4/0 cable. I have a similar situation that I’ve read about on this forum. The negative DC cable will run from the battery bank to a smart shunt, then to a (-) busbar, and (-) busbar to the inverter. On the positive side, the cable will run to a 400amp class T fuse, then on/off switch, second 400amp class T fuse, (+) busbar, then MultiPlus 3K 12v. What is the best ground solution for the inverter case? Should I run a separate ground to the chassis or run the box ground to the (-) busbar? At this point, the negative busbar is grounded through the chassis off a single negative cable attached to the Battle Born batteries - one cable running to the chassis. I assume, I don’t want to run an additional ground off the busbar. This would create a ground loop. Does all of this make sense? What is the best approach? Like you, I’ve seen the diagrams etc on this forum. It appears, people are running the case ground to the (-) busbar. Note: I live in the USA.

Multiplus-II
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jkmann answered ·

Basically the case ground point for the Multiplus must provide a ground path to the chassis for the full AC amperage that your Multiplus is set up to produce when not on shore power, AND it needs to provide a ground path to the negative busbar robust enough to blow the fuse to the Multiplus (400A in this case) in a fault condition. This is a separate path from the negative path from the Multiplus (-) power terminal to the battery.

You CAN use a separate chassis grounding point because the Multiplus case ground is only active as a DC ground in a fault condition. It should not create a ground loop in normal operation. On the other hand, you then also need a chassis ground back to the negative busbar capable of handling that amperage. So ask yourself ... where can you locate two chassis ground points that are actually capable of 400A? That's not an easy project on a van. Maybe some of the main structural members have that kind of capacity. Your better choice is to bring the Multiplus case ground to the negative busbar where it can blow your fuse in a fault condition without going through the chassis, and ensure that your chassis ground cable from the (-) busbar has adequate ampacity for all of the AC current that the Multiplus will deliver, plus any B2B charging loads and other loads that have their return path through the chassis.

If this doesn't clarify it, maybe it would be best for you to post a diagram.

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