grounding electrics and what about through hull fittings?

[LostinFrance]

Well I know I should have sorted this out before but I never did. So.... I have a boat with no anode except for the saildrive leg. I have a galvanic isolator on the shore power system and the negative busbar is linked to the engine. I'm only running a fridge and the normal stuff. I have a lead keel, so could I run a wire to that or should I fit an anode? And (please don't larf at me) if so from where? The engine block or negative busbar? What do I risk in doing nothing? - My keel cost a lot of money btw and I'm very fond of it, so if there is any chance of it slyly sneaking off, bit by bit over the years I'd be a bit put out.
Secondly, should I link the through hull fittings (all are good quality bronze -or so I was told) to an anode?
I'm a bit of a prat when it comes to electrics so any advice keenly accepted

 

[VicS]

Bronze (or DZR for that matter) skin fittings should not need cathodic protection. They should definitely not be bonded to anodes protecting anything else.

Your lead keel should be OK.

Although in the past I have argued strongly in favour of the shorepower earth being connected to the DC earth/negative and the anodes etc. I now know that ISO 13297 does not require this to be so provided the whole AC installation is protected by an RCD.

(It is however, still required, to the best of my knowledge by, the American Boat and Yacht Council, ABYC)

Not connecting the earth to the DC earth etc should prevent any corrosion problems caused by the shorepower. Also of course make the GI unnecessary.

It is I understand, possible for some mains equipment, using switched mode power supplies, to send a current down the earth thereby putting a GI into "conduct mode" and so preventing it from protecting anodes etc from corrosion.

What problems do you have. If none don't try fixing them but do not overlook the sail drive anode. That is vital.

Any evidence of corrosion of the keel then fit anodes to spcifically protect that, bonded to it and nothing else

 

[vyv_cox]

Advice nowadays is not to bond seacocks, as it is difficult to predict what the effect might be. For example, if some were tin bronze and some were a modified brass, such as DZR or manganese bronze, then a cell would be created between them, causing the latter to corrode more rapidly.

Adding a lead keel into the equation makes it more interesting. Lead is about 0.1 volt more electropositive than a typical bronze, plus it is far bigger than your seacocks. Bonding them together would increase the corrosion rate of the seacocks quite considerably. It would be very difficult to site an anode to protect them, unless they are all within a very close distance of each other (pretty unlikely).

By far the best solution is to look after the saildrive with its own anode. Leave the rest alone. Their corrosion rate will be very slow, especially the keel. Monitor them from time to time, annually is plenty.

So far as the mains electricity is concerned, this is complex and I'm not certain that earthing to the engine is the correct thing to do. I suggest you look at Nigel Calder's 'Boatowners mechanical and electrical manual' where this is covered fully. Other forumites may well be able to advise on this better than I.

 

[lw395]

The keel should be insulated by a proper coat of paint/epoxy.
Is the fridge mains? If so it probably needs to be earthed unfortunately. Otherwise my approach: RCD, double insulated charger etc and don't connect the mains earth to anything (except the RCD).
Do test the RCD from time to time!
There is a lot to be said for buying the Calder book or similar and following it, rather than taking a bit of advice here and there, ending up with a half and half system. There are more than one system of protection, and not all can be mixed at random.

 

[davidwf]

Like VicS I have recently been reading ISO 13297 and disconnected the mains earth from my boat -ve.

My prop shaft is isolated by an R&D flexible coupling and on the land shaft and engine were electrically isolated. However in the water with no mains connected I can see a circuit between shaft and engine. There is resistance between the two ( only had a rapitest meter with me so not sure how much).

I can also see a connection between the shaft and mains earth which I expect as the water is effectively earth. However it's the reading between engine and shaft that puzzells me my only thoughts so far are that the seawater in the cooling inlet pipe is allowing a circuit. Do you think that will be the cause?

 

[Airassmith]

Interesting. I'd just noticed that on my newish (to me) boat the mains earth is not taken to DC neg . I'd also just read somewhere (Calder ?) that this absolutely should be done and was about to install a wire. Now I won't, or should I ?

 

[VicS]

Yes I think Calder believes it should be (as does the ABYC) but it is not done on newish continental (EU?) built boats. At least that is my understanding of the current situation. Imperative though that the whole boat is protected by an RCD.

 

[pvb]

I thought that the European Recreational Craft Directive did require earth bonding, like the ABYC, the US Coastguard, the British Marine Electronics Association, etc.

 

[VicS]

[ QUOTE ]
I thought .....

[/ QUOTE ] Yes but Davidwf managed to track down a copy of ISO 13297 on line HERE which says,
"4.2 The protective conductor shall be connected to the craft's d.c. negative ground (earth) as close as
practicable to the battery (d.c.) negative terminal.
NOTE If an RCD (whole-craft residual current device) or an isolation transformer is installed in the main supply circuit of the
a.c. system (see 8.2), the negative ground terminal of the d.c. system need not be connected to the a.c. shore ground
(protective conductor)."

Hence my dramatic change in thinking.
It is very difficult to think up a dangerous situation if the vessel is protected by an RCD although it does mean that situations could exist in which the MCB would trip (or the fuse blow) if the connection between the shorepower earth and the DC system earth was made except that the RCD would probably trip first anyway!

Still a bit puzzled by the conflicting advice and standards etc.
When I was arguing that the two earths should be connected half the world seem to be arguing the opposite. Now I have changed my thoughts the other half of the world are against me!

Only one 100% satisfactory solution. Keep mains electricity and boats well separated!

 

[rogerthebodger]

One of the problems Vic is that the standards try to make a one solution for all situations.

IMHO in the case of a steel boat the potential faults and the dangers it may produce would be different to a plastic boat.

Standards and the dangers that are being protected against change with changes in technology. The introduction of RCD's are a case in point which is reflected in the note you refer to int he standard you point to. The new technology can also introduce new requirements which in normal life people are not normally aware of. The usual drum I bang is the importance of a good earth connection back to and connected the neutral of the supply which in the normal household is taken care of by the electrical supply company npower in the UK. On a boat where generators, inverters and or isolating transformers are common this important requirement is forgotten for a RCD to work at all.

My current thinking is on a plastic boat the mains earth or (protection conductor) as it has been refered to need only be connected to the metal cases of the mains appliances as by the nature of the plastic boat giving insulation between the appliance case of the sea or ground plain.

In my case steel boat or even a ferro, which IMHO should be treated as a steel boat needs the hull connected to the "protection conductor" as it is very possible for the case of an appliance to also be connected to the conducting hull thus the possibility of the hull itself becoming live if a live to case fault occurs.

As I said on a plastic boat this is unlikely as has been said the trend is not to connect all the metal fittings together and a common point and the DC ground and noe the AC protection conductor.

 

[pvb]

Does ISO 13297 take precedence over EU directives?

 

[LostinFrance]

Thanks for the replies, as I said I'm a prat when it comes to electrics. In fact, the fridge is 12v and every circuit (240v or 12v is protected by a RCD. I bought the system from Merlin Electrical and I am pleased with their stuff and their manuals. Unfortunately I have a very vague recollection of someone telling me I should fit a hull anode for extra security. In my old boats I only ever had a shaft anode and the seacocks were never bonded either - it's just that with a spanking new boat I want to get it right.
Interesting about the keel, yes of course it is protected with a very good coat of epoxy, so no point attaching a wire to it then? /forums/images/graemlins/confused.gif

 

[vyv_cox]

A bare lead keel would probably be just as corrosion resistant. In water with moderate pH, which seawater is, lead forms a passive film that resists corrosion. Which is why lead pipes still remain in service since Roman times. Don't risk messing things up by adding wires and anodes.

 

[VicS]

[ QUOTE ]
I have a very vague recollection of someone telling me I should fit a hull anode for extra security

[/ QUOTE ] What is this anode going to protect? The most vulnerable thing I guess, the sail drive leg. So if you want to go down that route fit a hull anode close to the saildrive and bond it to the saildrive and nothing else. Powerboat owners with stern drives sometimes opt for a hanging anode (but you can't really get one all that close to a saildrive).

It might extend the life of the sail drive leg marginally but at least it should still be giving protection if the anode on the drive leg wastes away a bit faster than anticipated or you find you self in a situation where you are unable to lift the boat to replace it when necessary.

 

[galeus]

I've read your post with interest as I was just a couple of days away from buying a galvanic isolator.The replies you,ve received say that current regs. mean that G.I. is no longer req. or needed.The main anxiety driving me to buy the G.I. was when we are moored to a pontoon connected to shore power and my battery charger comes on I assumed that the interface between the AC and DC thus created would then have access to my anodes;am I misunderstanding things?Help please - /forums/images/graemlins/confused.gif Richard

 

[VicS]

I have had a PM from galeus drawing my attention to his question above. I have replied but I copy the text of my reply here for others to comment.

The galvanic isolator (GI) is likely to be required when a boat is normally connected to a shorepower supply, even if the supply is not actually in use, due to a variety of reasons that can cause corrosion of under water bits and pieces, particularly the anodes.
Basically these all boil down to galvanic corrosion because the shore power earth connects your anodes (if they are bonded to the the shorepower earth) to all sorts of things around you. The steel piling in the marina, the steel boat in the next berth etc. You then have the classic dissimilar metals situation. Steel and your zinc or aluminium anodes (your outdrive or saildrive even) connected together by the earth connection and immersed in the same bath of seawater. Result the less noble zinc or aluminum corrodes away.

The voltage that drives this process is fairly small and can be blocked by a couple of diodes. That is basically what you find in a GI. If a fault to earth on the AC system occurs because the diodes are switched on by voltages higher than the galvanic ones it conducts the fault current to earth so enabling the fuse to blow or the MCB to trip.

(The GI actually contains a pair of diodes facing one way and a pair facing the other way so that it conducts both halves of an AC wave)

That's very briefly the reason for fitting a GI and the way in which it works, by blocking currents from very low voltage sources such as galvanic ones while allowing current from higher voltage sources such as the AC mains to pass.

One of the things I learnt recently is that switched mode power supplies, as in computers and modern battery chargers etc can lead to small currents in the earth connection, which, being from a high voltage source, turn on the GI and therefore render it useless in blocking the currents from galvanic sources. Even devices with contact arc suppression fitted will do it I suspect.
There's an explanation of that and of the theory behind GIs in the technical section of the Smartgauge website. (Some very well written stuff on a variety of topics there.)

The other thing I learnt recently is that ISO13297 (Deals with AC systems on small craft) does not require the shorepower earth to be connected to the DC system earth etc provided there is an RCD protecting the whole vessel. Other standards do still require it though.

Interesting thing is that when I was campaigning for the DC and shorepower earth to be connected I was constantly fending of arguments that they should not be. Now that I have, partly at any rate, changed my stance I am fending of arguments saying that they must be.

If the shorepower earth is not connected to the DC system and the anodes etc it should solve all the problems associated with the corrosion it might cause if it were.

You ask

"The main anxiety driving me to buy the G.I. was when we are moored to a pontoon connected to shore power and my battery charger comes on I assumed that the interface between the AC and DC thus created would then have access to my anodes;am I misunderstanding things"

As already explained the galvanic problem exists all the time the Shorepower is plugged in regardless of whether or not it is in use. You battery charger, while it is on, might just prevent the GI blocking galvanic currents but its DC output should not cause any problems unless you have something seriously wrong. Then the GI would not be any use anyway as 12 volts is more than enough to make it conduct. So yes I guess you are misunderstanding things a little.

I hope this helps. I'm still on the fence a bit about whether or not to bond the shorepower earth to the DC earth/negative. I have downloaded a couple of articles from "Professional Boatbuilder" by Nigel Calder but I still have to find the time to read and digest them. Maybe then I'll come to a more positive conclusion.