Simple 230v socket and an earth connection to 12v neg?

[Dellquay13]

I have the most basic of shore power setups on my boat. A shore power inlet wired to a 16a rccb to one twin 13a socket.
At various times this socket gets used for a kettle, phone charger, a little oil filled radiator or a ‘double insulated’ 12v smart charger for my batteries (3a fuse in the mains plug). No inverter or anything clever. If I’m using 230v then I am in the marina connected to shoreside earth. I only plug into shore power when I’m on board, without exception it’s unplugged from the marina mains when I leave the boat.

Why do I need to connect the shore power earth to my 12v negative and my engine and shaft anode?

If I really really must earth up my engine I can, and while I am financially embarrassed I can build a metal cased 350a galvanic isolator from bits already in my cellar, but I’d like to know why it is so necessary on such a basic installation.

 

[Tranona]

Yes, Galvanic isolator on input and earth direct to water if possible, You can use a hull anode or a dedicated button anode. Personally wwould not do it through the 12v circuits or the engine. Your "simplicity" is irrelevant as it is having 230v on the boat and used, not how many users you have.

 

[PaulRainbow]

I have the most basic of shore power setups on my boat. A shore power inlet wired to a 16a rccb to one twin 13a socket.
At various times this socket gets used for a kettle, phone charger, a little oil filled radiator or a ‘double insulated’ 12v smart charger for my batteries (3a fuse in the mains plug). No inverter or anything clever. If I’m using 230v then I am in the marina connected to shoreside earth. I only plug into shore power when I’m on board, without exception it’s unplugged from the marina mains when I leave the boat.

Why do I need to connect the shore power earth to my 12v negative and my engine and shaft anode?

If I really really must earth up my engine I can, and while I am financially embarrassed I can build a metal cased 350a galvanic isolator from bits already in my cellar, but I’d like to know why it is so necessary on such a basic installation.

The setup you describe is safe enough, you are under no obligation to connect the shore power Earth to "12v negative or your engine and shaft anode"

It is a requirement for new build boats to have an Earth connection to the water, you don't have to.

 

[Dellquay13]

The setup you describe is safe enough, you are under no obligation to connect the shore power Earth to "12v negative or your engine and shaft anode"

It is a requirement for new build boats to have an Earth connection to the water, you don't have to.

Thanks, the confirmation that my existing setup is safe in principle is reassuring.

My question about connecting the earth via the 12v neg ultimately to the shaft and anode was based on not having any other existing hull anode to connect the earth to. If I decided to connect my earth to water without additional holes in the hull, I suppose I could suspend an anode overboard on a stainless cable and add a GI, but I don’t see any major increase in safety gained from the extra complexity.

 

[William_H]

A galvanic isolator is really only needed for 24/7 type connection to mains to avert possible galvanic corrosion. If all your appliances are double insulated ie no metal parts exposed and connected to mains earth then you have no need for connection to water etc. ol'will

 

[PaulRainbow]

Thanks, the confirmation that my existing setup is safe in principle is reassuring.

My question about connecting the earth via the 12v neg ultimately to the shaft and anode was based on not having any other existing hull anode to connect the earth to. If I decided to connect my earth to water without additional holes in the hull, I suppose I could suspend an anode overboard on a stainless cable and add a GI, but I don’t see any major increase in safety gained from the extra complexity.

For what you describe in post #1 there is no benefit to you adding a connection to the water. There are millions of boats out there that pre-date the requirement to have such a connection, all sailing around happily.

 

[Dellquay13]

This article in the current YM made me question whether I needed to connect the shore power earth on my basic mains setup to my engine and 12v neg (as I don’t have a dedicated hull anode) but I couldn’t see any major benefit for me, hence my question.

How to prevent corrosion on your yacht - Yachting Monthly

 

[Refueler]

I defer to Alistair Garrod book on Boat Electrics : "Electrics Afloat" - where he describes fully the effects and viability of the connections ..

A book I thoroughly recc;d .... its a PBO recc'd book as well.

 

[jamie N]

You've the boats 12VDC, which will almost certainly have an earth to water on it, gawd knows how difficult it is to avoid one. Your 240VAC is basically an entirely different, and isolated circuit, that hasn't a clue that it's on a boat, any more than your boat knows that it's got a 240VAC socket running a kettle. There's nothing in common (see what I did there!) with them. Fabricating a common earth will 'potentially' lead to them giving a combined 'negative' effect.

 

[Dellquay13]

You've the boats 12VDC, which will almost certainly have an earth to water on it, gawd knows how difficult it is to avoid one. Your 240VAC is basically an entirely different, and isolated circuit, that hasn't a clue that it's on a boat, any more than your boat knows that it's got 240VAC socket running a kettle. There's nothing in common (see what I did there!) with them. Fabricating a common earth will 'potentially' lead to them giving a combined 'negative' effect.

This is why I was struggling to find a compelling reason to earth my mains socket to water through the only path I could see.
Without realising I could open the can of worms that is fitting a dedicated hull anode to a boat that has lasted 44years without one, I didn’t like the idea of my 12v and propeller having a connection to everybody else’s anodes.
Especially since 4 out of the 5 boats immediately adjacent to me are liveaboards who have 24/7 shore power and haven’t been lifted for any maintenance work in years, I doubt they have any anodes left.

KISS

Maybe I need to unsubscribe from email links to simplistic articles that make blanket statements, and only follow guidance that has been fact checked and curated by a reputable source. (So why am I still typing on a forum?)

 

[PaulRainbow]

This article in the current YM made me question whether I needed to connect the shore power earth on my basic mains setup to my engine and 12v neg (as I don’t have a dedicated hull anode) but I couldn’t see any major benefit for me, hence my question.

How to prevent corrosion on your yacht - Yachting Monthly

"For safety reasons, the shore supply’s AC earth should always be bonded to your vessel’s own grounding circuit, which in itself will be connected to all of the metallic components on board including the engine, propshaft, saildrive and skin fittings."

This statement is incorrect for a number of reasons. Engines are not always connected to the anodes, they are not in the water and they are often fully isolated from anything else. The propshaft may or may not be connected, it might have it's own anode, same with the prop itself. Many saildrives are isolated and have their own anodes, connecting those would be very risky indeed. Skin fittings are contentious, some people insist they should be connected, i (and many others) say that they should not. A skin fitting, in isolation, will not be subject to corrosion, but if it is bonded and there is a problem, it can be affected. I've seen it first hand where there was a corrosion problem and the skin fittings were corroded, this obviously means that there is a real risk of the skin fittings failing and consequent loss of the boat.

Safety reasons may be an issue, but that will depend on the AC installation, in your case there is not benefit of such a connection.

As i said, all new boats must have a connection from the boats AC Earth to the water, this can be made using the hull of a metal boat, the vessels ground plane (if one exists) or an anode. I would not connect to the engine, gearbox, saildrive etc. If none available i would fit a small button anode.

Yours is not a new boat, so you are under no obligation to make such a connection, but you could if you so desired. It would involve fitting the button anode (assuming you don't have a suitable one to connect to). Doing so now leaves you open to corrosion problems, so you must fit a galvanic isolator.

If you do not make the connection you cannot be subject to the SCC Duncan Kent refers to and you do not need a GI.

 

[PaulRainbow]

This is why I was struggling to find a compelling reason to earth my mains socket to water through the only path I could see.
Without realising I could open the can of worms that is fitting a dedicated hull anode to a boat that has lasted 44years without one, I didn’t like the idea of my 12v and propeller having a connection to everybody else’s anodes.

This is the key and that's why you would need the GI. 44 years without is also very relevant.

Especially since 4 out of the 5 boats immediately adjacent to me are liveaboards who have 24/7 shore power and haven’t been lifted for any maintenance work in years, I doubt they have any anodes left.

KISS

Maybe I need to unsubscribe from email links to simplistic articles that make blanket statements, and only follow guidance that has been fact checked and curated by a reputable source. (So why am I still typing on a forum?)

I do this for a living

 

[Refueler]

I'm with Paul ....

Why fit what has not been there before ?

Has there been any sign of corrosion that prompts thoughts of connecting ? Is it just reading someones blurb ?

When I had my mounts and engine changed - Alan disconnected the grounding wires that bridged the shaft coupling ... isolating the engine / gearbox and shaft from each other and rest of boat.
We could find no reason to have it ...

20 odd yrs later .. all is fine ... prop shows no sign whatsoever of pitting / corrosion ... all's well.

My latest boat has loads of connecting wires from keel bolts to all sorts BUT 240 is NOT grounded with 12V -ve ... I'm not changing anything in that order ... - but will monitor to see what happens over time. As I work through the electrics - I will of course get to see aspects ..

 

[Alex_Blackwood]

For what you describe in post #1 there is no benefit to you adding a connection to the water. There are millions of boats out there that pre-date the requirement to have such a connection, all sailing around happily.

+1 As Paul says not needed and from other posts in this thread it is obvious that there is a lot of somewhat misleading information around on this subject.
I would however entreat you to ensure that your shore connection is in good order at all times. Regularly inspect and check continuity of the cable. Also test your RCD with the test button if nothing else.

 

[BabaYaga]

Thanks, the confirmation that my existing setup is safe in principle is reassuring.

My question about connecting the earth via the 12v neg ultimately to the shaft and anode was based on not having any other existing hull anode to connect the earth to. If I decided to connect my earth to water without additional holes in the hull, I suppose I could suspend an anode overboard on a stainless cable and add a GI, but I don’t see any major increase in safety gained from the extra complexity.

This is why I was struggling to find a compelling reason to earth my mains socket to water through the only path I could see.
Without realising I could open the can of worms that is fitting a dedicated hull anode to a boat that has lasted 44years without one, I didn’t like the idea of my 12v and propeller having a connection to everybody else’s anodes.

Consider a scenario like this: You are working on your boat afloat, let's say replacing the sink drain hose. It is early spring and cold, so you have brought along an old fan heater, which you plug into your socket. The fan heater works but has developed an internal fault, meaning that live AC current leaks to its metal case. Meanwhile, the protective earth lead in the shore power connection has for some reason been compromised. Unlikely, but not impossible.
If your shore power installation had had a PE connection to the water, the RCD would have tripped as soon as you plugged in or turned on the fan heater. If not, the RCD will not trip until you yourself provide the 30 mA path to ground by touching the the case and the skin fitting at the same time.
Anyway, this is my understanding of why the requirement (for new boats) is in place.

 

[Stemar]

While I'm not an electrician, I do understand how circuits work, and I've yet to see Paul give advice that I wouldn't be happy to follow.

 

[Buck Turgidson]

Consider a scenario like this: You are working on your boat afloat, let's say replacing the sink drain hose. It is early spring and cold, so you have brought along an old fan heater, which you plug into your socket. The fan heater works but has developed an internal fault, meaning that live AC current leaks to its metal case. Meanwhile, the protective earth lead in the shore power connection has for some reason been compromised. Unlikely, but not impossible.
If your shore power installation had had a PE connection to the water, the RCD would have tripped as soon as you plugged in or turned on the fan heater. If not, the RCD will not trip until you yourself provide the 30 mA path to ground by touching the the case and the skin fitting at the same time.
Anyway, this is my understanding of why the requirement (for new boats) is in place.

And what is the statistical probability of that happening compared to the statistical probability of the common earth put in to protect against it failing?

I have a portable caravan unit for shore power, should I rip it apart and bond the earth?

 

[Alex_Blackwood]

Consider a scenario like this: You are working on your boat afloat, let's say replacing the sink drain hose. It is early spring and cold, so you have brought along an old fan heater, which you plug into your socket. The fan heater works but has developed an internal fault, meaning that live AC current leaks to its metal case. Meanwhile, the protective earth lead in the shore power connection has for some reason been compromised. Unlikely, but not impossible.
If your shore power installation had had a PE connection to the water, the RCD would have tripped as soon as you plugged in or turned on the fan heater. If not, the RCD will not trip until you yourself provide the 30 mA path to ground by touching the the case and the skin fitting at the same time.
Anyway, this is my understanding of why the requirement (for new boats) is in place.

Unhelpful fantasising.

 

[PaulRainbow]

Consider a scenario like this: You are working on your boat afloat, let's say replacing the sink drain hose. It is early spring and cold, so you have brought along an old fan heater, which you plug into your socket. The fan heater works but has developed an internal fault, meaning that live AC current leaks to its metal case. Meanwhile, the protective earth lead in the shore power connection has for some reason been compromised. Unlikely, but not impossible.
If your shore power installation had had a PE connection to the water, the RCD would have tripped as soon as you plugged in or turned on the fan heater. If not, the RCD will not trip until you yourself provide the 30 mA path to ground by touching the the case and the skin fitting at the same time.
Anyway, this is my understanding of why the requirement (for new boats) is in place.

But you still don't get an electric shock, even after the most unlikely set of faults/coincidences.

 

[Dellquay13]

I can understand the theory behind the belt and braces approach to PE on new boats. It’s imperative to have the water earth if an inverter is fitted making 230v available when there is no shore earth. I don’t have an inverter.

In lieu of this on my old boat I have been relying on good husbandry of electrical equipment and a considered RAMS to control risks from hazards, and to reduce the chance of one ‘if’ cascading through several more ‘ifs’ into a disaster.

Maybe magazine articles should be consigned to the category of mild interest pieces while in the dentists waiting room