Shore Power - Is this safe?

[PaulRainbow]

Like most yachts, mine has a 12v DC internal supply and a 240v AC shore power connection via an RCD.

I had assumed that these were entirely separate, and the 240v supply was earthed back to the marina post. But I've just discovered a green-and-yellow wire I hadn't ever noticed before. This connects both the 240v neutral and earth lines to the DC negative line, at the point where it is 'earthed' to the sea through the propeller shaft.

Electricity isn't my strong suit, but this feels iffy. Is this normal practice - is it safe?

You are almost certainly mistaken about the green/yellow wire. If the incoming AC neutral and earth are connected before the boats RCD, the marina RCD will trip, if connected after the boats RCD, the boats RCD will trip. If the boat does not have an RCD, the marina one will trip.

It's simple, shore power AC neutral and earth are bonded shoreside, prior to the marina RCD, not on the boat.

On new installations it is a requirement to connect the incoming earth to the vessels bonding circuit. Depending on various factors, this connection could be made in a variety of places, but the end result will be that there is a connection between the AC earth, DC negative and the water.

Older boats can also be wired like this, when re-wiring systems i'll generally update boats accordingly. In this type of installation, a galvanic isolator should be fitted.

Your green/yellow wire could be one of two things. a) a connection from AC earth to DC negative b) part of the anode bonding circuit, this circuit is usually wired with green or green/yellow wire.

 

[Refueler]

Seems unfortunate to have a shore power system without a battery charger, though. That's the main purpose of it as far as I'm concerned, since I rarely have any 240v appliances on board to plug in.

Pete

Please go back to my earlier post before that and you will see that I do have a battery charger as you say - its one of the greatest benefits.

The beauty of a battery charger is that they are 'double earthed' and are designed to keep both power sides isolated.

 

[RupertW]

Seems unfortunate to have a shore power system without a battery charger, though. That's the main purpose of it as far as I'm concerned, since I rarely have any 240v appliances on board to plug in.

Pete

Sounds like that works for you but we tried to make the boat seem like a floating home when guests come aboard so all cabins have domestic double sockets which quickly get used by them and us for laptops, fan heaters (in winter), phones and hair dryers. We will get an electric kettle and an induction hob that sits on the gimballed gas stove at some point.

But then for the rest of the time out at sea or anchored it’s 5 USB ports from the battery and no hairdryers which people get used to. Never thought of spending the money on more than a cheapo Halfords charger which now sits in a cupboard as solar does the rest.

 

[Refueler]

That book is almost 30 years old. For many years, the accepted advice is that AC earth should be connected to DC ground.

Second ... that Alastair Garrods book .... which is promoted by PBO ... also goes into great detail about this ... in fact has complete section on the problems of connected and non connected AC earth etc.

So its 30yrs old book .... never thought electrics was subject to Darwin ? Given that in 30yrs most countries have changed very little in power distribution ... OK - I will accept that a few countries that were still radial are now installing ring main ... YES there are some still with radial !!

Suggest Chapter 7 and 8 of Alastair Garrod's book Electrics Afloat ... ISBN 0-7136-6149-6 ...... In fact the whole book ... !!

 

[KellysEye]

As said fit a galvanic isolator otherwise you risk corrosion, the propellor is one as are the anodes.

 

[Refueler]

Any idea why it’s frowned upon? I have this set up, including charging a bowthruster battery in the forepeak, and it all seems to work OK. There is a galvanic isolator on the shorepower.

Here in Latvia - we still have radial circuits in houses and I have fought hard to have rin main in my rebuilt house and outbuildings. While agreeing all this with the electricians - luckily I had guys who had worked in UK so understood my request for Ring Main .... were talking about ENR.
Now I am not an electrician ... I have qualifications in AC DC theory etc. but as far as wiring goes ... I follow the plans set by those trained in it. But as I understand it ... ENR relies on the power supplier having grounded correctly and that no socket / appliance or item in your house / distribution has an error in which is connected. This is compounded by having as I have 3 phase to my estate and then divided into single phases. Over here we have the typical (I think its terrible ... ) EU various plugs and sockets ... some with earth some without ... ALL are non polar so can be plugged in any way round ... unlike UK / USA.

I'll leave it to experts to correct my above if wrong ...

 

[Refueler]

+1, or something similar.

Not a book in which you can have confidence.

Funny that people still reference such as the 12V Bible ... which is even older !

I've been searching for more 'up to date' definitive info ............ strange that the argument of connect or not is STILL prevalent ... that it is NOT decided as implied by some here.
That in fact it appears that Shore Power provision at least in UK is setup with the assumption that we as boaters do not connect AC earth to DC ground.... regardless of which is correct.

I think Garrod sums it up well : P88 .. where he remarks about people bringing shore side knowledge / part knowledge onto boats and not understanding the dangers ....

I think I'll stick with Yates and Garrod rather than forum comments.

 

[Refueler]

Your system isn't exactly frowned upon, it's how boats used to be wired, millions of boats were, and still are, wired this way. Connecting the incoming AC Earth to the boats grounding circuits is a modern requirement and where this system is used a galvanic isolator should be fitted.

To run your DC systems from AC you wouldn't fit a AC-DC transformer. Your battery charger should do this. If it doesn't, fit a better battery charger.

Thank you for confirming what is common ...

As regards battery charger to run the DC side ... I have a double bank of 90 - 100A/Hr accumulators which give more than enough power and the 4A charger is fine to top them up while alongside. Boat is a motor sailer as well - so 50% of the sailing time ... the old Perky 4-107 is thumping amps into the battery bank ! Both batterys rarely drop below 80% charged ...

I have considered a Caravan style power panel (marine of course ) that looks after charging / powering DC circuits etc. but to be honest after many 2 week cruises with the existing setup and not running out of 'juice' ... its a luxury that is unnecessary.

 

[VicS]

Funny that people still reference such as the 12V Bible ... which is even older !

I've been searching for more 'up to date' definitive info ............ strange that the argument of connect or not is STILL prevalent ... that it is NOT decided as implied by some here.
That in fact it appears that Shore Power provision at least in UK is setup with the assumption that we as boaters do not connect AC earth to DC ground.... regardless of which is correct.

I think Garrod sums it up well : P88 .. where he remarks about people bringing shore side knowledge / part knowledge onto boats and not understanding the dangers ....

I think I'll stick with Yates and Garrod rather than forum comments.

The standards which dictate what is correct are ISO 13297:2018 for the low voltage AC installation, ie the shorepower system, and ISO 10133:2017 for the extra low voltage DC system. These provide the up to date definitive info you are searching for.

Early editions of ISO 13297, prior to the introduction of the 2012 edition, allowed the DC negative not to be bonded to the shorepower earth provided the AC system included an RCD protecting the whole craft. This was something of an anomaly when compared with the standards for caravans etc where this was not allowed however one must expect some older boats, wired before 2012, not to have the DC negative bonded to the shorepower earth.

 

[rogerthebodger]

Unless the DC system is a fully isolated system the the DC negative and shorepower earth should be connected, although this was not always a requirement

The neutral should not be connected to either the shorepower earth or the DC negative

I assume we are not talking about a shore power system using an isolating transformer.

Vic

The first statement "Unless the DC system is a fully isolated system the the DC negative and shorepower earth should be connected, "

This statement interest me in what is considered as a "fully isolated system DC system" as its is now considered that anodes not connected to the DC negative and with a flexible coupling the engine will be isolated.

The connection of the mains earth to any metal fittings outside the boat will provide a secondary earth point in case the wired earth wire in the shore power connection is compromised.

The question of a battery charger is a question of the type (does it have an isolation transformer). If it doen't it has no place on a boat.

We discussed the neutral/earth connection on a boat before and you did some tests and confirmed that the RCD would trip. This is because of an alternate route bypassing the boat RCD.

This of cause assumes that there is no incoming isolation transformer on board. This would require a neutral/earth connection on board.

My own boat has the DC system totally isolated from the hull, so I have not mains earth/DC negative connection. I do have a mains earth connection to the steel hull via a GI.

 

[pvb]

So its 30yrs old book .... never thought electrics was subject to Darwin ?

Even though you live in Latvia, there's no reason why you shouldn't follow modern safety advice on boat electrics.

 

[oldharry]

I understood that on the Continetal mains supply the voltage swings from zero to +110v then swings back through zero to -110v, thus giving 220 across the wires, but only 110v above earth. Unlike UK where the AC negative is at earth potential, so that the live wore carries the full 230v above earth.

If thats right then the OPs arangement would be to sya the least dodgy ina French Marina, particualrly as I have found quite often that the French often wire their sockets back to front, as it makes no difference in their system. I use my polarity reversing adapter surprisingly often on french Campsites. That could mean that OPs boat ends up connecting a French 'live' supply to the boat's neutral and earth with potentially spectacular and dangerous results!

 

[BabaYaga]

This statement interest me in what is considered as a "fully isolated system DC system" as its is now considered that anodes not connected to the DC negative and with a flexible coupling the engine will be isolated.

This is what the ISO 10133 (2012 edition) has to say on the matter:
"system in which both positive and negative poles remain isolated from the ground (earth).
Example: Systems in which the positive and negative poles are not connected to the water through a metallic hull, the propulsion system or earthed trough the a.c. protective conductor.
Note: Some systems may use momentary ground connection for engine starting purposes and may remain isolated".

I would agree, if I understand you correctly, that a GRP boat with no connection between DC negative and any external anodes and with an unbridged flexible coupling should be considered to have a fully isolated DC system. I would guess such setups are not rare but quite common.

 

[VicS]

Vic

The first statement "Unless the DC system is a fully isolated system the the DC negative and shorepower earth should be connected, "

This statement interest me in what is considered as a "fully isolated system DC system" as its is now considered that anodes not connected to the DC negative and with a flexible coupling the engine will be isolated.

The connection of the mains earth to any metal fittings outside the boat will provide a secondary earth point in case the wired earth wire in the shore power connection is compromised.

The question of a battery charger is a question of the type (does it have an isolation transformer). If it doen't it has no place on a boat.

We discussed the neutral/earth connection on a boat before and you did some tests and confirmed that the RCD would trip. This is because of an alternate route bypassing the boat RCD.

This of cause assumes that there is no incoming isolation transformer on board. This would require a neutral/earth connection on board.

My own boat has the DC system totally isolated from the hull, so I have not mains earth/DC negative connection. I do have a mains earth connection to the steel hull via a GI.

A fully isolated DC system is defined as one in which both positive and negative poles are isolated from the ground or earth. In other words no connection to the water through a metallic hull, the propulsion system or earthed via the AC system protective conductor. It is recognised though that some engines may need a brief earth connection for engine starting.

It is my understanding of ISO 13297 that the AC system protective conductor ( shorepower earth) should be connected to the hull of metallic hulled craft.

 

[rogerthebodger]

I would agree, if I understand you correctly, that a GRP boat with no connection between DC negative and any external anodes and with an unbridged flexible coupling should be considered to have a fully isolated DC system. I would guess such setups are not rare but quite common.

That is exactly what I am thinking.

It used to be "standard" for the anodes and underwater metal fittings to be interconnected and also connected
to the DC negative.

On a GRP boat where most of the underwater fittings are insulated from each other by the GRP there should be no need for anodes. The stern drive being one exception with a bronze prop and stainless steel shaft.

Most boats have a flexible coupling (rubber or plastic) so without a strap that is also isolated.

The only other issue is a cheep mains battery charger. On mine its had a mains transformer which isolates the DC from the mains side. I also have a switch on the output to select which of my 3 battery banks I can charge with an off position.

I went for the isolated DC system as I did not wish to have any DC currents flowing through my steel hull. My anodes are welded to the hull and a shaft anode even through my prop is a stainless steel fabricated and fitted to a stainless steel shaft.

 

[Refueler]

Even though you live in Latvia, there's no reason why you shouldn't follow modern safety advice on boat electrics.

Totally agree ... but even today the argument prevails as to what exactly is the single definitive system. Inland Waterways have one ... Recreational Directive another ... USA another ..... etc. etc.
Just because a person follows one directive - does not make it universal.

I work in an industry that has potential for mass destruction and safety is drummed in day after day ... it is not something I take lightly.

 

[pvb]

Totally agree ... but even today the argument prevails as to what exactly is the single definitive system. Inland Waterways have one ... Recreational Directive another ... USA another ..... etc. etc.
Just because a person follows one directive - does not make it universal.

As far as I'm aware, the following authorities say that AC earth should be bonded for safety reasons:-

* the European Recreational Craft Directive
* the British Marine Electronics Association
* the American Boat and Yacht Council (ABYC)
* even Nigel Calder in "The Boatowners Electrical and Mechanical Manual"

I reckon that's reasonably definitive.

 

[rogerthebodger]

As far as I'm aware, the following authorities say that AC earth should be bonded for safety reasons:-

.

The AC earth should be bonded to what and who does that bonding protect and how.

 

[Refueler]

As far as I'm aware, the following authorities say that AC earth should be bonded for safety reasons:-

* the European Recreational Craft Directive
* the British Marine Electronics Association
* the American Boat and Yacht Council (ABYC)
* even Nigel Calder in "The Boatowners Electrical and Mechanical Manual"

I reckon that's reasonably definitive.

The point is NOT just AC earth bonded, but the dual bonding of DC ground and AC earth.

If anyone doesn't bond AC earth ... which in fact is covered by 3 pin cabling / sockets to shore ... they have to be mad. Continuity of the earth connection is required.

Trouble is OP brought in the question of AC neutral, AC Earth and DC Ground being all connected together.

I know for me ... and I know I'm not stupid !! The thread has covered a lot of material and has also highlighted a few items that I think have become mixed in some posts / thoughts ...

Forgive the 30yr old terminology but in this has relevance :

AC 3 pin is as old : Red = +ve, Blue or Black = -ve, Green = Earth ... later changed to Brown = Phase, Blue = Neutral, Green yellow = Earth

DC as far as I know still carries usual Red = +ve and Black = -ve.

I for one have no problem with AC earth being connected to send to ground any potential that occurs when fault. But I am not so sure I wish to have AC neutral which is one side of the power phase similarly connected.
Second - I can accept DC equipment having -ve connected to ground ... most engines will do that via shaft if not isolated ... but with AC neutral connected as well ?

I think I prefer to play safe and keep 240V well away from 12V thank you ... as various books and online sites comment - imagine a 240V fault and all that potential then hits the grounding !! I prefer that potential to go via the earth return in the cable to shore.

Call me stupid ... call me what you like ... I'll keep mine segregated ....

 

[JumbleDuck]

That book is almost 30 years old. For many years, the accepted advice is that AC earth should be connected to DC ground.

I believe that is forbidden in the US. Perhaps their electrons are different from ours.