AC DC common ground

[goboatingnow]

Originally Posted by pdqsailor

I happen to agree with you.. I had a CENTRAL GFCI installed... there is no connection from my AC ground to the DC ground.. we are in fresh water nd I do not want our boat to have a pathway to discharge stray currents into the water and with a central GFCI .. the boat and the occupants are protected.. I do not CARE what ABYC says - I care about not providing a pathway to kill anyone and be safe on board our boat.. The GFCI does this while on shore power or when sailing with our inverter as the source of AC power..

I fully agree with a rcd installed and one on the pillar l also I ensure no earth or neutral ever is connected to sea water or earth or dc negative

[donradcliffe]

Amen. If you want to protect the kids and props, talk the club into installing RCI breakers in the dock power system.

[pdqsailor]

Originally Posted by donradcliffe

Amen. If you want to protect the kids and props, talk the club into installing RCI breakers in the dock power system.

Our club in rewiring the electrical did indeed install RCI breakers in the dock power system.. AND they work,, they slam the entire dock down TIGHT and a strobe light flashes off... until the breaker is manually reset..

However multiple boats this season suffered stray current corrosion to their propellers, one to a keel and a propeller right next to me.. Our boat having its AC ground isolated from the DC bonding system suffered zero damage. How do I protect us on our boat with either shore power or the inverter? I have a central GFCI breaker and if there is a fault to ground.. it trips and shuts the boat down regardless of AC source be it shore power, inverter or a portable generator..

Circuit is shore power connection - inlet breaker - inverter/charger - central GFCI breaker - distribution panels - appliances.. No AC connection to DC ground... including at the inverter charger...

The history of ABYC's mandates is that they first demanded that the AC ground can discharge power safely into the water - but not so safe for fresh water that has 70 x more resistance... and not safe for animals or people in that water.. Later recognizing that DANGER they added ECI but it allows for up to 30 ma of discharge six time more than the 5 ma as a GFCI does 30 ma is sufficient to cause electro shock drowning..

So I am NO fan of ABYC where boat wiring is concerned...

[YANDINA]

So if your GFCI is not working and your shore power battery charger shorts AC to DC there is NO HARD WIRE PROTECTION. The life of your swimmers is dependent on some electronics with no backup system. Perhaps ABYC is over protective but there is a reason for it.

[pdqsailor]

Originally Posted by YANDINA

So if your GFCI is not working and your shore power battery charger shorts AC to DC there is NO HARD WIRE PROTECTION. The life of your swimmers is dependent on some electronics with no backup system. Perhaps ABYC is over protective but there is a reason for it.

first off .. my battery charge is integral to the inverter... and in the event of a short - there are two input GFCI's to the shore power, first is the shore power pedestal breaker - and it is tested once a week by ME... and second is the clubs main breakers for the dock circuit.. and I have SEEN these work - they are quite dramatic shutting off the entire power to the dock... Actually the primary purpose of the central GFCI on board the boat - a more SENSITIVE device than the ABYC suggested ECI is to protect the occupants of the boat while we are off of shore power using the inverter.. and it works.. and it is tested regularly...

The idea that boats can - and DO discharge AC power with a fault into the water and in our case FRESH water in close proximity to the Junior Club beach where children and dogs venture into the water - we are talking 20 FEET here...is arrogance and recklessness.

Keep in mind that ABYC is not a sanctioned legal authority such as UL, ULC, CSA or the NFPA - they would LIKE to be.. they are NOT.. they are an industry appointed body... with NO legal authority... however they may well be legally liable for mandating that which is arrogant and reckless.

[goboatingnow]

Originally Posted by YANDINA

So if your GFCI is not working and your shore power battery charger shorts AC to DC there is NO HARD WIRE PROTECTION. The life of your swimmers is dependent on some electronics with no backup system. Perhaps ABYC is over protective but there is a reason for it.

In my case there are 4 RCBO between me and the water. Hence all 4 would have to simultaneously fail to expose asa swimme

Even between the marina pillar and me there are 3 RCDBOs. Frankly my dear ABYC hasn’t a clue

[Jolly Roger]

I read about half of this thread until I became more confused than before I started, as I suspect also is the OP.
For starters, I wish the ‘experts’ would not use acronyms without first stating what they stand for. All of us know what AC and DC means, (I hope), but some of the others are a complete mystery to me.

Then there are the direct contradictions between one reply and another. There are also the contradictions between marine electricians, so if I use such a person, how do I know he’s giving me the correct advice? I also agree that a little knowledge in this subject can be a very dangerous thing, but it is to be hoped that the people who post genuinely think they are correct and are not trying to kill us or sink our boats.
So what is a poor ignorant fellow supposed to do? Switch it on and see what happens?
The grounds on my shore power, (I have two), are not connected to my DC 12 volts grounds. If they should be, why do we have both? Why not just have one big buss and connect all the ground wires on that?
Just asking.

[goboatingnow]

The point really depends on the safety perspective

If you rely on multiple in line RCD protection then the old fashioned concept of “ grounding everything “ is largely redundant. The grounding mentality stems from the desire that the ground system will blow any protective devices ( ie fuses ) if any hot wire makes a ground connection Like through seawater

If you follow this approach then everything has to be grounded especially everything that could have a live fault , this extends to your dc system as well.

The trouble is now the extensive ground earth bonding system is itself a source of ” risk ”

These days both with multi stage RCD protection and potentially isolating transformers ( or even quasi ac dc boats which are effectively isolated anyway. There is much less justification for the “ ground everything “ approach

Hence there are “ calls” that need to be made based on your approach.

My own view is isolating transformers should be mandatory. It’s funny that on building sites in the U.K. they are whereas in marinas they are not ( even if soon they will most likely be added to the code )

Isolating transformers should really be fitted to any boat with extensive AC assets in my view. This removes all meds for grounds and removes most potential shock paths.

[pdqsailor]

Yes... the ISO standard in the UK and in Europe is an actual legal standard and it is sensible.. it Works.. ABYC and their initial call to bond grounds later amended to bond grounds and to install ECI breakers (mitigating the risk they caused with the grounding) is NOT any kind of authority with legal standing.. They dream about being one... they are not.. Multiple boats on our dock were built in Europe or like mine are purposely wired to not make an AC ground connection to the DC bonding system... a much bigger deal for us as we operate in fresh water which is 70 times the resistance to salt water conductivity...so the danger area in fresh water is severe... This year why did this rear its UGLY head.. boats were damaged from a source of stray current...

[pdqsailor]

Originally Posted by Jolly Roger

I read about half of this thread until I became more confused than before I started, as I suspect also is the OP.
For starters, I wish the ‘experts’ would not use acronyms without first stating what they stand for. All of us know what AC and DC means, (I hope), but some of the others are a complete mystery to me.

Then there are the direct contradictions between one reply and another. There are also the contradictions between marine electricians, so if I use such a person, how do I know he’s giving me the correct advice? I also agree that a little knowledge in this subject can be a very dangerous thing, but it is to be hoped that the people who post genuinely think they are correct and are not trying to kill us or sink our boats.
So what is a poor ignorant fellow supposed to do? Switch it on and see what happens?
The grounds on my shore power, (I have two), are not connected to my DC 12 volts grounds. If they should be, why do we have both? Why not just have one big buss and connect all the ground wires on that?
Just asking.

About thirty years ago I was plunged into this issue... I knew a lot about boat wiring at the time but not about this issue.. so I had to educate myself.. I read, I traded messages with ABYC senior engineers.. I read stuff by the National Fire Prevention Association (a body that has legal standing) and I came to conclusions.. one of which was that while ABYC in a salt water environment had a point with some validity that this was a dangerous reckless and irresponsible thing for boats operated in fresh water..

So like I had to become educated .. so do you and you also have to think critically and get your information from MULTIPLE sources to arrive at a well rounded and informed bigger picture and make up your OWN mind as to the best way to proceed...

[goboatingnow]

Originally Posted by pdqsailor

About thirty years ago I was plunged into this issue... I knew a lot about boat wiring at the time but not about this issue.. so I had to educate myself.. I read, I traded messages with ABYC senior engineers.. I read stuff by the National Fire Prevention Association (a body that has legal standing) and I came to conclusions.. one of which was that while ABYC in a salt water environment had a point with some validity that this was a dangerous reckless and irresponsible thing for boats operated in fresh water..



So like I had to become educated .. so do you and you also have to think critically and get your information from MULTIPLE sources to arrive at a well rounded and informed bigger picture and make up your OWN mind as to the best way to proceed...

Your last paragraph is indeed correct blind faith in so called largely “ advisory “ standards are no substitute for clear thinking and informed decision making

Ultimately you make your vessel safe.
In my view therefore. I do not bond anything to seawater if at all possible and I rely on RCBO to ensure my vessel is safe. I am however fitting an isolating transformer to improve my vessels safety and recently orders a toroidal one of suitable ratings. I will have to add soft start to this unfortunately and I will protect it with RCBOS as necessary

[pdqsailor]

I fully agree with you... I have to research isolation transformers.. here we do not have 220 volts.. and at 110 VAC and thirty amps I expect that the transformer will be large, heavy and expensive..

[goboatingnow]

Originally Posted by pdqsailor

I fully agree with you... I have to research isolation transformers.. here we do not have 220 volts.. and at 110 VAC and thirty amps I expect that the transformer will be large, heavy and expensive..

Well yes that’s the issue the toroidal ones offer the best weight advantage. A charger invertor combination could also be used depending on exact requirements. I’m fitting ac230 vac 3kw unit ( Hammond manufacturing )

[goboatingnow]

Sorry I should have said Airlink transformers

17kg for a 230vac 3000va unit £230

[s/v Jedi]

I have a request and a question:

R: can someone pm/email me the ISO document about shore power, RCD and isolation transformers?

Q: under ISO and when using an isolation transformer: is the RCD between inlet and isolation transformer mandatory or does it allow an exception because of the isolation transformer?

For the thread: you can improve on the RCD and removing any jumpers between AC and DC by utilizing an isolation transformer. Not only does this eliminate all risk for swimmers but also for people on board. It is the clear winner for safety and that is added to the galvanic protection for the boat.

I added the diagram, which shows a standard 2-pole breaker after the inlet.