Marine application and grounding

[Kommy000]

Hopefully I posted in the right forums, I'm hoping some of the users did the same conversion and had to deal with the same setup and questions like this one. Little background story: converting sailboat from diesel to electric motor. Ended up like everyone else buying 20 cells from Amy, with 16 for 48v propulsion bank and 4 to replace my house bank.
Did test build with 12v 4 cell bank, all works and running great.
Just finished 48v bank and connected it to my solar 400w array via Midnite Solar MPPT and small breaker box to be able to shut off on both sides of the MPPT.
Now I'm in the process of removing diesel engine and of course I see some grounding green wires going back to the panel which I think is connected to AC side ground bus bar. After removing diesel engine do I just connect that green wire to the metal mounting brackets of the electric motor and then maybe follow that wire and connect to the grounding screws on MPPT case and small breaker box? Right now I have no grounding wire going from any of those.
Researching grounding online, first, seems like I'm supposed to connect AC ground bar to the negative on DC side so both DC current and AC current have same ground. I don't think mine are connected since I don't see actual wire connecting the main negative DC bar and ground AC bar and they about 8" apart. So do I just connect 8 or 10 gauge green wire from DC negative bar to AC ground bar?
Also, electric motor mentioned casually that they recommend connecting 48v bank DC negative to 12v bank negative for grounding purposes also. Both banks are completely separate and 48v bank doesn't even go to the DC electric panel because it only being used/will be used as a propulsion bank. So again, do I just run 8 gauge green wire from negative to main DC panel negative which runs off the 12v bank? And again, if I connect that negative to AC ground I guess that would mean 48v bank is grounded too now?
I apologize for a long questions but I was hoping someone on these forums had to deal with this on their boat, since I see more and more people doing conversions out there on sailboats and most of the time seems like they end up using same cells , though really cells don't matter or what battery they used, this is more of a common sense grounding. Just trying to figure out how to ground the system properly or even if I need to do that.
What made me questions my grounding is that not having AC ground connected to DC negative on the AC/DC electrical panel and also as of now I have not galvanic isolator which I should be installing in a few days once I receive the part.
Thank you for any advice you can give me.

 

[12VoltInstalls]

“Ground” is a funny word in automobiles, RVs, and even weirder in boats.

yes you should ‘ground’ every negative to a common point and (review ABYC code for correct methods) AC green/bare/“ground”/white needs to be terminated properly as well. You DEFINITELY don’t want to mix your DC neg(-) with any AC nuetrals and that happens more often than you would think.

Because every boat is an anode floating in electrolyte for one thing. For another, you don’t want stuff to start “unplating itself” or dissolving while connected to shore power.

 

[Kommy000]

“Ground” is a funny word in automobiles, RVs, and even weirder in boats.

yes you should ‘ground’ every negative to a common point and (review ABYC code for correct methods) AC green/bare/“ground”/white needs to be terminated properly as well. You DEFINITELY don’t want to mix your DC neg(-) with any AC nuetrals and that happens more often than you would think.

Because every boat is an anode floating in electrolyte for one thing. For another, you don’t want stuff to start “unplating itself” or dissolving while connected to shore power.

And here why I'm getting confusing answers. Here is the link to west marine and point 4 talking about connecting ac ground to DC negative https://www.westmarine.com/WestAdvisor/Ten-Deadly-Conditions

 

[wholybee]

Google "abyc e-11" and get reading.

It's far too complicated to address in a post. If you are doing a complete rewire (or close) I would suggest following ABYC by using yellow for DC negative instead of black. Presumably, you have some sort of metal gear drive or similar that will be electrically connected to the propshaft and prop, That _could_ be used as a common grounding point, but it doesn't need to be. My diesel engine is completely isolated (even with a special starter and alternator that don't ground to the block) to prevent/reduce, the need for changing my shaft anode. Really, all you need is a common buss bar.

Regarding connecting grounds together. Multiple ground points *must* *only* be connected via one path. So, your old diesel engine block was grounded by necessity via the starter and alternator. You said you also thought that an AC ground wire was connected to it. Therefore, so too were the AC and DC ground bars connected, even though there was no wire between them. Connecting them together would create a second path, and current would flow in a loop, potentially causing various difficult to diagnose problems.

 

[Kommy000]

Google "abyc e-11" and get reading.

It's far too complicated to address in a post. If you are doing a complete rewire (or close) I would suggest following ABYC by using yellow for DC negative instead of black. Presumably, you have some sort of metal gear drive or similar that will be electrically connected to the propshaft and prop, That _could_ be used as a common grounding point, but it doesn't need to be. My diesel engine is completely isolated (even with a special starter and alternator that don't ground to the block) to prevent/reduce, the need for changing my shaft anode. Really, all you need is a common buss bar.

Regarding connecting grounds together. Multiple ground points *must* *only* be connected via one path. So, your old diesel engine block was grounded by necessity via the starter and alternator. You said you also thought that an AC ground wire was connected to it. Therefore, so too were the AC and DC ground bars connected, even though there was no wire between them. Connecting them together would create a second path, and current would flow in a loop, potentially causing various difficult to diagnose problems.

Ok it makes sense that they connected at the engine between ac and DC, didn't think about it. So theoretically I can just connect those together to get common ground for both ax and DC.
Per electric motor vendor, it is isolated from prop shaft so it's not connected to water so I'm guessing there is no need to connect ground wire to the motor?
And if not, do I just ground MPPT and Breaker box cases to a separate green wire just running to the same ac ground bar at the electric panel?
I also see that the old green engine ground wire was connected to the through hull on the way to the electric panel

 

[12VoltInstalls]

You are confusing the safety ground (green) AC ground a little bit.
You need to read the ABYC and answer your questions because it will also illuminate the single path of “ground” for you.
in essence the AC and DC sides need to be installed independently as if the other ‘side’ doesn’t exist. Then a common point (bussbar) connects the AC panel green and all the home-run DC neg(-) wires. You don’t just enter the neg(-) circuit at some convenient place which is sorta what you described.

 

[12VoltInstalls]

~>duplicate post<~ deleted

 

[Kommy000]

Thats the thing I'm reading all the info and it doesn't really explain the real life implementation of ground.
On my electrical panel I have a common negative bar for 12v house battery and all the DC breakers/circuits . On the other side of the panel there is AC panel with separate bus bar for all AC green cable connections. From reading all the literature it says to have common ground for both AC and DC. So from what I understand you don't just ran a short 8" wire to go from common DC negative bus bar and connect it to AC bus bar, so I would have to create another bus bar and now connect DC negative bus bar and AC green bus bar to this new bus bar? To me it seems it does the same function as a single wire connecting two existing bus bars but I can see the advantage for clean layout with separate common ground bus bar. And if that is the case, then do I run another green wire from that common ground bus bar to something like engine and maybe one of the thruhulls? That is what confusing, I can read code and other literature but seems like there is no real life example how to do that. I have no inverter, only will be galvanic isolator but only on AC side before it enters the AC panel, so everything is pretty straightforward.

 

[wholybee]

Don't complicate it. Use a meter to determine if they are connected now. If they are, do not add a second connection. If they are not, then connect them.. The details about where/how they are connected is not as important as they are connected in only one place.
And don't confuse bonding with grounding. Through hulls are bonded. That is not the same thing as grounding- it serves a very different purpose. Did you read ABYC E-11?