Boat Electrical Grounding: 230V + AGM- + LifePO4- to Same Ground?

DIY
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OK, so I started a “little” project to add solar to my boat and while making a box for my battery with my skill saw, while on shore power, some wires melted. I discovered in fixing this issue, that 1. Shore ground was not connected to my Mastervolt Mass GI input, 2. There was no (required) breaker/GFCI on either the input or output of the Mass GI, 3. The 230v shore power system was not grounded at all, 4. Without grounding a GFCI is not even possible, 5. My new LifePO4 needs to be grounded somewhere 6. My new inverter needs to be grounded somewhere, and last but not least 7. The whole internet seems to be conflicting over whether you can just ground the LifePO4 negative to the AGM negative which IS grounded, on the engine.

The ‘expert’ that I brought in to help said GFCIs are a waste and basically the same as breakers anyway.

Where am I now? Well the melted wires are replaced with far thicker, tinned wires, and connected properly with Wago connectors, inside a properly sealed junction box.

But my 230v system, and my LifePO4 system are fully ungrounded. So no GFCIs and no breakers/fuses, and no safety on the 230v system. And the Mastervolt instructions say to connect the ground wire with the neutral (negative) wire and then ground them both together.

And I want to add a Victron Orion XS DC to DC charger, but this has a common ground which I assume would go to the AGM negative terminal, since that’s where the whole 12V system is grounded to the engine. And this is where the internet blows up in my face with conflicting data.

Some say ground the AGM and LifePO4 to the same engine ground, which is to say- and let’s be extra clear about this- connect the negative terminals of the LifePO4 and AGM batteries!

Some say that will cause your antifouling paint to fall off and your zinc protective parts on your prop shaft to melt away.

Some say this will destroy both batteries.

Victron’s wiring unlimited has one chart showing both battery banks’ negative terminals sort of connected, but through a Victron shunt, but not directly (I don’t have a Victron shunt).

None show the 230V system grounded to the 12v battery negative posts, to the engine.

OK, I’m officially stuck.

The one thing the internet seems to agree on is that the number one cause of death on private boats is- fire, caused by bad electrical installations. Wonderful.

If I follow some instructions I will: 1. Wire my Mass GI negative to the Mass GI ground, to the LifePO4 negative terminal, to the AGM negative terminal, to the engine. Somehow this seems totally scary connecting both 12v battery types AND the 230V to a common ground.

Please help lay out all these snakes in a straight line :slight_smile:

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find a better expert to help you.
start with local Victron dealers, if no luck find the local Victron rep and ask for a good dealer recommendation.

GFCI do not need a ground to work, so anyone that tells you otherwise don’t use them.

all battery negatives should be connected (unless there is a very specific case for an isolated system)

this is beyond a quick online help thread, someone needs to get hands on that knows what they are doing to help you get this properly sorted.

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Kevin, thanks for the response.
I’m sure you’ll see why I’m so confused. When it comes to boat electrical, apparently everyone has a different opinion on just about everything. Anyway so the point about GFCI’s requiring a ground come from page 61 of Victron’s Wiring Unlimited (link below):

“Earth leakage detection can only take place in systems where the neutral conductor is connected to the earth conductor; like
in a TN or TT system. Earth leakage detection is not possible in an IT network.”

And also page 62:
“An AC power source needs to have a neutral-to-earth link (MEN link) so that an RCD can operate. This is the case for the
grid, but also if the AC source is a generator or an inverter.”

https://www.victronenergy.com/upload/documents/The_Wiring_Unlimited_book/43562-Wiring_Unlimited-pdf-en.pdf

OK, so all battery negatives need to be connected, and since it’s a boat, that means that they are all going to be grounded where the AGM batteries are currently ground- to the engine. OK, fine. I’m at least getting some consensus on this point. Thank you.

However it still concerns me that I will also need to ground the 230V shore power system, and (apparently) the boat side of the Mass GI only has one option- connecting the ground to the neutral wire, then to the negative terminals of the batteries mentioned above. OK so I’m connecting 230V to my batteries. Is it just me to whom this seems bizarrely wrong? I mean that’s what they’re calling for I guess (link below page 10):

“The Protective Earth (output terminal) must be connected to the central grounding point of the
vehicle/ ship.
The neutral conductor (N) of the AC output of the Mass GI must be connected to the safety ground
(PE/GND) and a ground fault circuit-interrupter (GFCI) must be integrated in the wiring of the AC
output”

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in re to GFCI
they look for current leaving them to be the same as the current returning, if there is less current returning a difference of 5ma in US and 30ma else where it trips, it does not need a reference to ground as it only looks that current leaving and returning, if less returns it is leaking or faulting to “ground”

you should install a GFCI on the load side of the inverter before any loads

in re to grounding or correctly said bonding (electrically connected)
all metal on the boat needs to be bonded to insure equal potential on all metal, so yes you need to connect all metal and battery negatives electrically together, this is for life safety and also on a boat corrosion resistance.

so you are not connecting the 230v to the batteries as you would think, you are bonding all the metal and battery negatives to the grounding conductor of your electrical system.
so all metal, battery neg, inverter frame, inverter ground terminal all together, the inverter ground relay will tie the neutral to the grounding bond when in inverter mode.

this is essential so that if the 230v hot line or the DC positive come in contact with any metal on the boat, that metal has a low impedance path to the source, IE inverter or batteries to allow enough current to flow to quickly trip or blow over current protection device.

if the return path for a short is a high impedance path, then it will heat up and that is a potential source of fire, and fire is bad.

for shore power you should install an isolation transformer, this will separate the shore ground and the boat ground, and at that point you no longer care if the shore power has a ground.(while you are in the water)
adding a circuit breaker on the line side of the isolation transformer sized properly for the cord and connectors you are using will protect you even if the shore power is not protected correctly.

you can also get a shore power cord with an inline GFCI at the male end to add protection to the cord and boat.

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Your not connecting 230V to the batteries, you are tying all the things together that need to be grounded, namely all battery negatives and the protective earth conductor of the inverter output. You generally want one single connection per system to ground. So a negative busbar gets a connection to ground, therefore the whole negative side of that DC system is now grounded.

But im sure theres exceptions, so you may want to keep the battery negatives ungrounded. Same for whether or not you need, or even should, connect the grounding system to the boats hull is an entirely different question, but i cant answer those. Thats where an actual boat specialist would need to support you.

Connecting the inverters AC output neutral conductor to protective earth/ground is what lets a GFCI/RCD work. There should also be only one such connection in a TN-S (terre-neutre separe/earth-neutral separated) system. In a Victron inverter this is done automatically by the earthing relay.

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Kevin and Chrigu,
You both referenced the ‘inverter’, where I was actually talking about a Mastervolt Mass GI Isolation Transformer :wink:

Does that change anything???
Thanks again!

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first post
“My new inverter needs to be grounded somewhere”

again you should find someone qualified to help or do the work, I don’t think you should be undertaking this work.

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Oh yeah, I forgot the inverter has a ground on the frame of it, on the back…
The 230V I was referring to was coming from the Mass GI.
Anyway, I guess that doesn’t change your post. Thanks :slight_smile:
And yeah, I need to find a good boat electrician!

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Just to add something into the mix, inland boat in the UK, steel hull. Our regulations are that all batteries are connected to the hull at a single point, usually the engine bearer as the engines are mounted on rubber mounts, so the engine block gets connected to this same point. The 230V ac also is also connected to the same hull point. If shore power is used, then a galvanic isolator is inserted between the shore earth wire and the hull, or in my case, an isolation transformer. Neutral and earth are connected on the outlet of the isolation transformer as this is a voltage source. When not on shore power, the Multiplus automatically connects earth to neutral. My hull and anodes have not dissolved after 4 years, my batteries (AGM starter and lithium house bank) have not had any issue. Tens of thousands of boats wired like this in inland UK waters.

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Hi Pwfarnell,
I guess I just thought it strange to connect the isolation transformer’s neutral and ground, because it’s AC. In AC as I understand the current pulses from the positive then from the neutral so both lines are ‘hot’ which is why you can plug into an AC socket upside down and it doesn’t matter. Now we’re going to go and ground one of those ‘hot’ wires. What am I missing here?

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Ok, sorry my mistake, i didnt look up what that device was and just assumed its an inverter. I dont think it changes much, since the output neutral of it would also need to be grounded

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OK great, thanks for clarifying :slight_smile:

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As you already noticed, grounding is not an easy topic. Im a trained and certified electrician, working for almost 20 years mostly in larger low voltage systems including generators, and i dont know all of it. And theres certainly still today discussions to be had between experts from the regulatory bodies on how to properly ground certain things, and even after those discussions there might still be asterisks in the code that might say “but in X situation, do Y instead”.

Tying the neutral conductor to ground is what defines it to be the neutral. If you dont ground it then theres no neutral conductor, then you are correct, its just two phases or hots. This would be an IT system (isole terre/isolated ground).

Using an IT system is not inherently wrong (but it might be against your local rules though). It can be more dangerous in certain situations, thats why the TN system is wider spread (at least in low voltage and to my knowledge)

I think the wikipedia page about those systems cover the basics fairly well

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This is why I stated I am in the UK as things vary country by country, in the UK we have neutral, which should be at or close to 0 volts and live which varies from plus to minus. Therefore, in the UK our plugs only fit one way into the sockets. This is why you need to know what your local rules are.

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Chrigu and Pwfarnell,
Thanks for both of your replies, very interesting.
This has been a very informative thread!
So I guess that the actual instructions list that I had was correct, as crazy as it sounded. Plus I need to ground some extra metal stuff that I hadn’t considered. Plus I need to put a GFCI on the output side of the inverter, which I had not considered. So good stuff. Thanks again all!

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6 posts were merged into an existing topic: Electric boat, propulsion and house battery, Cerbo GX monitoring and MP II AC power supply

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Think theres a language barrier here. AC power is Active and Neutral. Some countries also have earth which is exactly that a high conductive metalic rod in the earth usually copper and usually does f all in places like Australia with no moisture in the ground. Your AC power source never goes to ground in any application. DC has positive and negative and contradictions of negative going to earth is controversial. The larger the mass the better the earth and that includes engines which are earthed/negative to a lead mass being the battery. Cars have 40,000v AC and DC from 5mv in their ecu and to some sensors to high amperage 12 volt units and earth is earth its the body the engine which often has a cable between engine and body and body to negative battery and all works in harmony. Iv worked on cars where no matter how good your techniques are for joining a cut wire the car will go into panic attackor limp mode. German engineering they looked at water and said “how can we make this more complicated” Your answer to earth in a boat is as much mass of metal as possible like the engine and it can be a 2.5mm 200meter run. Neutral treat it as a live wire and dont connect your AC neutral to earth. Iv rewired many boats I hope this helps and I doubt you need a “sparky” Corrosion or electrolusees I can explain simply to but thats easily avoidable by good connections and correct sized cabling and insulation and your hull or engine wont become a sacrificial rod. Legally if you can or cant is upto you

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Grego77, are you commenting on Jan’s install or mine???

Sorry Jan, no offense, but I think you need another thread because I’m getting confused now on the advise that’s to you and the advise that’s to me.

I thought we had it settled that my 230V output from my isolation transformer would go to ground with the neutral and ground wires coupled together and all run with both battery systems’ negatives, to engine ground.

Please verify this.

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Topic cleaned up, moan at me if you are not happy. @jrmartin505 Grego77’s reply left as I have no idea what / who this was aimed at.

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No moaning here, it looked like you moved it at exactly the same time I was trying to move it. :folded_hands:

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