Shore power earth

colind3782

colind3782

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I'm about 2/3 of the way through the first fix of rewiring the 240 volts on the boat. Now it's an old Spanish boat that had no RCD or earth and here in Spain, an earth is few and far between. What's the best way of earthing the system on the boat? Engine block? Separate earthing block? The French couple who berthed next door had an earth lead connected to a metal block which dangled over the side. His reckoning being that you don't get a much better earth than the water in the marina. A tidier system would be appreciated :)
 
Fit an isolation transformer to isolate you boat completely from the dodgy Spanish electricity system

Ground one side of the secondary winding to an internal "earth "system thereby creating your own neutral. Don't worry about connecting it to the planet's surface.

Fit an RCD in the normal way
 
VicS said:
Fit an isolation transformer to isolate you boat completely from the dodgy Spanish electricity system

Ground one side of the secondary winding to an internal "earth "system thereby creating your own neutral. Don't worry about connecting it to the planet's surface.

Fit an RCD in the normal way
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+1
 
colind3782 said:
I've fitted the RCD and have plenty of earth wires just looking for a home. The engine mount seems favourite at the moment as I already have a route through the bulkhead for the wiring.
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Create a a common earth connection point above the level of any bilge water. Whether on not your engine block and DC negative are connected to this earth system depends upon your engine electrics . The DC negative should be connected to it if is not an isolated system

You should refer to the current edition of ISO 13297 which is the relevant international standard for AC systems in small boats
 
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VicS said:
Create a a common earth connection point above the level of any bilge water. Whether on not your engine block and DC negative are connected to this earth system depends upon your engine electrics . The DC negative should be connected to it if is not an isolated system

You should refer to the current edition of ISO 13297 which is the relevant international standard for AC systems in small boats
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Cheers :)
 
Am I missing something here? In the UK whatever the earthing arrangement in the boat is, it is connected to an earth on the marina supply. It sounds to me that in the OP that no such earth exists in the marina supply to connect the boat earth to. How is that resolved?
 
colind3782 said:
The French couple who berthed next door had an earth lead connected to a metal block which dangled over the side. His reckoning being that you don't get a much better earth than the water in the marina. A tidier system would be appreciated :)
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So when he gets a dead short to earth in any of his appliances he sends a blast of AC up through your skin fittings - nice! Probably creates a load of stray current corrosion as well, so I'd watch your underwater metal bits like a hawk!
 
l'escargot said:
Am I missing something here? In the UK whatever the earthing arrangement in the boat is, it is connected to an earth on the marina supply. It sounds to me that in the OP that no such earth exists in the marina supply to connect the boat earth to. How is that resolved?
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dk said:
So when he gets a dead short to earth in any of his appliances he sends a blast of AC up through your skin fittings - nice! Probably creates a load of stray current corrosion as well, so I'd watch your underwater metal bits like a hawk!
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Hence my suggestion to fit an isolation transformer to completely isolate the boat from the shoreside electricity supply, and to create an internal "protective conductor" system and equipotential boding
 
VicS said:
Hence my suggestion to fit an isolation transformer to completely isolate the boat from the shoreside electricity supply, and to create an internal "protective conductor" system and equipotential boding
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Totally agree.
 
nigelmercier said:
First thing you should do is fit an RCD.

Personally I don't have mains earth connected to any part of the boat; except mains appliances, and the metal switch panel which houses a couple of neon lamps and mains switches.
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I would agree on a GRP boat where all metal appliances tend to be insulated from each other.

On my steel boat I do have my mains connected to the steel hull and thus all metal cased appliances.

My DC negative is insulated from the hull as is my engine.
 
VicS said:
The DC negative should be connected to it if is not an isolated system
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Do you mean the DC negative should be connected to the mains earth "if it is not an isolated system".

You imply that if the DC system is an isolated system not mains earth connection is needed/desired/recommended.

If you mean an isolated system has the DC negative run a separate return wires. Don't most/all GRP boats have this arrangement and most/all metal boats have this arrangement to prevent stray currents in the hull to reduce the possibility of galvanic corrosion.
 
KellysEye said:
Along with the RCD fit a Galvanic Isolator to protect the boat from stray current corrosion.
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If there is no incoming earth conductor. Then there is no scope for fitting a galvanic isolator.

One of the OP's problems is the possible lack of a reliable earth in the power supply which is why I suggested an isolation transformer. Once a transformer is fitted there will be no connection to the shore earth even when one exists so need or scope for fitting a GI.

An isolation transformer, apart from its weight and bulk, is the best way of avoiding the galvanic corrosion problems associated with shorepower earth connections.
 
Rogershaw said:
Do you mean the DC negative should be connected to the mains earth "if it is not an isolated system".

You imply that if the DC system is an isolated system not mains earth connection is needed/desired/recommended.

If you mean an isolated system has the DC negative run a separate return wires. Don't most/all GRP boats have this arrangement and most/all metal boats have this arrangement to prevent stray currents in the hull to reduce the possibility of galvanic corrosion.
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Yes by isolated system I mean that the DC negative has separate wiring and does not use the engine block as a common return. Some grp bots have an isolated system. Most, at least among the smaller ones AFAIK, do not. Maybe more common on larger boats. I dont know. Some of course, esp where saildrives are involved, have hybrid systems with earthing relays etc. Volvo Penta, at least, have attempted to go down the route of isolation of the saildrive to avoid corrosion.

Metal hulls you know more about than I do but they should have a single earth connection point and if the DC system is not isolated and has its negative earthed it should be to this point. The hull must not be used (as a car body is )as the negative return at all.
 
Rogershaw said:
This is only needed on metal boats or where all underwater metal fittings are connected together and to anodes to reduce the wasting of the anodes.
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It is needed to protect underwater bits and pieces, in particular anodes, from corrosion due to "stray currents", from galvanic sources, which can be conducted to the boat via the shorepower earth connection.

If the shorepower earth connection can be eliminated by fitting an isolation transformer then there is no need for a GI nor indeed if there is no earth connection is there anywhere to fit one.

A GI will not offer any protection against stray currents from higher voltage sources, defective 12volt systems for example, which can lead to electrolysis.
 
I fully agree with what VicS knowingly writes and forgive me if I just repeat things. The isolation transformer is indeed the ideal solution, but let us be also practical: they are heavy, bulky and costly and only a few persons and/or boat dimensions can afford one. In case the shore power reliability is not certain, first of all it should be assumed to be totally floating (both live and no neutral whatsoever) and, second, the earth wire should not be used at all. The power can be still used safely within the boat if 1) both wires are always treated as "live" and dangerous (no neutral), 2) a good ground circuit is created onboard with a proper grounding plate in contact with the water, and 3) a good residual-current switch (RCD) is fitted.
Notice that at the end what I just wrote is almost the same (but nr. 1) if an isolation transformer was indeed fitted!

DC systems are another issue and, unfortunately, there is not a uniform agreement on the optimal configuration.

Daniel
 
Do consider that if in the case where an isolation transformer is used for the RCD to work the neutral and earth wire must be connected together at the secondary side of the transformer. If this is not done there will be no path to the residual current to flow bypassing the RCD for the RCD to trip.

This is exactly the same setup as the wiring of a substation in the UK type of power distribution configuration.
 
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