I've spent quite a bit of time researching this question, in the Wiring Unlimited document, along with the Multiplus manual and a multitude of forum postings. I realize some elements of the question are largely redundant so I will try and be as specific as possible. This installation is for a personal RV, and although I'm not a licensed electrician I have done quite a bit of high voltage electrical work, and as a computer scientist have had some exposure to electrical engineering principles and issues when working with microcontrollers, etc, though most of my work does not involve machinery or process automation. I'm by no means an expert, however.
I'm working to complete an installation of 2xMultiplus 12/3000/120-50 inverters connected to a 6x100AH Battleborn battery bank in parallel configuration. I also have a SmartSolar 150/85 MPPT controller connected to 7x195Watt PV panels mounted on the roof. The Multiplus units are in a split phase parallel configuration. Proper size wiring and current protection devices (breakers and fuses) on both the A/C and DC side are installed and various points(E.G. pre inverter A/C breaker, post PV combiner to MPPT controller, post MPPT controller to battery bank, post battery bank pre inverter, pre trailer existing wiring connection, post inverter A/C to trailer, etc). Properly sized wiring is used based on the current protection devices in place and maximum intended sustained amperage taking into account insulation rating, conduit fill rules (where applicable), etc.
At this juncture I have completed the majority of the installation on the system but have come to a question on proper ground application. Currently all equipment functions without grounding the equipment separately to the chassis(although I have full intention of doing so), and I have tested the system in excess of 250amps continuous DC flow to the inverters for extended periods of time(E.G. by turning on the A/C, electric hot water heater, etc). After working through a number of configuration "tuning" issues, I'm happy with the results, although an added element of safety is left dangling out there.
With that in mind, I believe the following is accurate:
1) Each Multiplus should be separately grounded to the chassis using a conductor of equal size to the conductors used in DC +- in the inverter. In my case 4/0 wire with 105c insulation.
2) The Solar MPPT controller should be grounded to the chassis, again with the same principle outlined in 1 regarding wire sizing.
In both 1 and 2, it would be alternatively acceptable to utilize a wire size equal to the acceptable size requirements for the current protection(e.g. for the battery bank a 300AMP fuse is used) device.
This brings me to my question(s):
Currently the negative and positive leads running to/from the inverters are connected to BusBars rated for 600A each. The positive side, prior to reaching the bus bars from the battery bank is fused, and then runs to a disconnect, then to the bus bar. The negative side, through a shunt and then straight to the BusBar.
One of the terminals on each BusBar runs off and connects to the main trailer wiring via the terminals where the previous manufacturer supplied batteries resided and then into the main trailer DC supply disconnect. This minimized the amount of rewiring needed to tie into the existing DC wiring. The positive side leading to the trailer manufacturer dc wiring is fused prior to reaching the existing trailer wiring system.
The existing trailer appears to have ran a frame chassis DC connection from the negative side of the DC wiring. Should I disconnect this and replace it with a larger 4/0 wire from the battery bank bus bar? Is it acceptable to leave it, and run an additional negative wire from the BusBar directly to the chassis(near the existing ground bar on the trailer)? Would/Could this create a ground loop/other situation with multiple DC paths to the chassis ?
Additionally, since the Multiplus requires a ground, should I route that to the negative BusBar, instead of a separate ground out to the chassis, and then use the larger ground noted above? The same applying to the MPPT controller. Similar to this:
https://community.victronenergy.com/questions/25415/installing-the-multiplus-3000.html
In the aforementioned diagram, it would appear all negative and ground connections are terminated on the same negative busbar, and then a single chassis ground is ran to the frame. If that is the more suitable way to approach it, would it be necessary to disconnect the existing DC negative to chassis run the manufacturer installed(I would think so)? How would energizing the inverter chassis with high voltage A/C impact the DC negative connected equipment in the case of a short to the inverter housing using a common busbar scenario(or for that matter into the chassis) ?
I'm trying to determine the most ideal path forward to ensure safety and minimize complexity. The wiring space is extremely constrained as well. Any recommendations are much appreciated.
Thanks in advance for any thoughts.
Chris
