Simple Shore Power

[timb]

I am new to boat ownership and would like to know the easiest (read cheapest) way of getting mains power on board for powering a heater or dehumidifier etc. Is it just a case of running an extension lead from the marina power points or are there other issues to consider such as galvanic isolation etc?

By using the simple method of an extension lead will I have any problems with corrosion? What about RCB's and RCD's?
I have looked on the Internet a lot for this subject but can't seem to get a simple answer.
I intend in future to install proper shore power with sockets in the boat etc. Will I then need to connect the 240v ground to the negative side of the 12v DC system? If so why and where?
Also, I believe I only have to install a galvanic isolater if the 240v ground is connected to the negative side of the 12v DC system is this true?

By the way this is happening on a 1987 Sadler 26 which will be berthed in a fully serviced marina most of the time.


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[sailorman]

do a search on this forum " shore power" u will find all u req.

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[steve_cronin]

Run your heater from an extension lead. it will do no harm whatsoever to your boat's metal bits unless it is connected to them.

When it comes to installing a fixed system the galvanic isolator goes between the earth pin on the inlet to the boat and the boat's earth. Every other earth or 12volt negative is connected on the boat side of the isolator. NOTHING is connected to the shore side of it except for the shorepower earth.

There are other points concerning shorepower and GIs but I'm just answering your question as put. See:-

http://www.sterling-power.com/ click "products" then Galvanic isolators, for an explanation.

Steve Cronin

<hr width=100% size=1>The above is, like any other post here, only a personal opinion

 

[msimms]

You may be interested in the site I found today, click <A target="_blank" HREF=http://tinyurl.com/4hmhe>here</A>

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[chriscallender]

I'm sure you will get conflicting opinions but the simple extension cable worked fine for me last winter, the marina power socket usually has an RCD so some protection there (although you could also fit one of those socket ones at the boat end of the extension cable which in my case had a normal domestic 13A socket).

About galvanic corrosion I had no issues (anode, prop etc were fine after 6 months of heater/dehumidifier) but I would be really careful about using something like a battery charger that could link mains earth and the boat ground as you say. In a marina you can get galvanic corrosion in a marina even without shore power from a neighbour's dodgy installation so I don't think you are adding much extra risk by running a heater and dehumidifier as long as they are not in any way electrically connected to the boat (eg sitting on top of a metal sink or something).

Chris

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[timb]

Thanks very much for the help.

I have something still bothering me though.
If it is okay to run an extension lead in, so long as it is not connected to the boats 12v circuit, why can you not install a totaly seperate 240v system and still not have it attached to the 12v circuit - thereby eliminating the need for a galvanic isolator?
In other words why do you have to connect to the 12v circuit?

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[msimms]

I think it's for safety, should your mains lead go faulty (wire exposed) and come in to contact with metal work of the boat, the boat could go live. Next time you touch both the boat and the earthed pontoon you make the circuit and could get a belt. Could be nasty or could be just a tingle.

Had a mate living in a residential caravan which developed an earth fault. Every time you opened the metal door you got a slight belt. It was his dog that got the worst of it though when it touched its nose to the door asking to come in one night it got a belt. Poor thing didn't half yelp. Electric company sorted it next day, bad earthing rod I think it was.

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[anabel]

One small thing which you are probably aware of & that is , if you are near the shore power & have a long lead or cable on a drum or reel, then make sure to uncoil all or most of the cable. Otherwise you could have over heating of the wire. Last year there was a nearby church burnt down as a result of a heater connected to the mains via a reel of cable!
Rgds.
E.

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[Guest]

Many boats don\'t ....

there are a few schools of thought on this subject. Many books have been written and literally not one agrees 100% with any other.

I bought a collection of books .... about 4 and also downloaded various pdf files of internet etc. A combination of them doesn't even answer it fully.

Me - and this is where many will cry - SHAME - ..... has main cable in to caravan external socket in cockpit. This then direct to Consumer box with 2 main breakers. One breaker serves the two domestic sockets (1 in fore cabin, other at aft end of main cabin). The other breaker is ready for lights / chargers etc. that will be fitted next year when I put wallet back in order !!

I do not have 12V or 240V connected to any isolators or ground plates on the boat ..... the breakers should trip as in a household system if any stray milli-amps occur.

Right now I'm putting my flak-jacket on while forum experts load up their ammo .....


<hr width=100% size=1>Cheers Nigel ..... <A target="_blank" HREF=http://www.geocities.com/solentlifeuk/>http://www.geocities.com/solentlifeuk/</A>

 

[Trevethan]

One of the main uses of shore power is to run a battery charger -- which by definition links shore and 12 volt systems. If you didn't plug in a charger I guess you could do without an isolator.

I think the problems of galvanic actions are most acute for metals boats, wood and plastic on suffer at their sumbermerged fittings and only then if there is a problem.

I have no galvanic isloator and I don't connect shore and 12 volt earths. The RCDs work -- a heater melter a cable and the system went pop as it should. In the two years since I fitted the system comprising a domestic cinsumer unit, rdc and mcbs, I haven't noticed any change in anode depletion.

Hope helps.

Nick



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[Guest]

Charger\'s .... ??

Maybe I'm wrong but a charger even though connects to 12V and 240V - the two voltages / systems are completely separated and should not effectively combine ......

I believe it would have to be a catastrophic incident inside the charger to short between the two supplies ??


<hr width=100% size=1>Cheers Nigel ..... <A target="_blank" HREF=http://www.geocities.com/solentlifeuk/>http://www.geocities.com/solentlifeuk/</A>

 

[timb]

Re: Charger\'s .... ??

Thanks for all the info.
I think for know I will run an extension lead to my heater or dehumidifier and look seriously at a proper shore power installation in the future.

Does anybody know how the Sterling battery chargers connect to the battery bank?
I am sure it would not be a case of a couple of large crocodile clips??
I guess it would be by a permanently wired connection through the 12v circuit - Here we go again connecting the 240v to the 12v circuit!
I have 2 75 ah batteries on a Sadler 26. Neither is a dedicated starter (10hp Volvo) or house battery, they are alternated between duties.

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[Trevethan]

Re: Charger\'s .... ??

You may well be right, but I seem to remember reading somewhere that the charger could be a method of tying the two together and getting small differences in poential between boat, power station and water and current could flow. Maybe that was only the case if you employ a joined 240 and 12 volt earth?

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[Trevethan]

Re: Charger\'s .... ??

I have a sterling three bank 50 amp charger charger a pair of 200 amp hour truck batteries

I have twinned two of the three outputs, as per Mr Sterlings instruction and connected that to one battery. I used a suitable ring connector crimped to the wire then bolted onto the battery clamp. I run the single to the other battery +ve.

The negative runs to the battery -ve. I suspect I will be pulled up on that and people will suggest running to the engine earthing stud, but it makes for a shorter cable run so...

cheers,

Nick

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[steve_cronin]

Re: Charger\'s .... ??

Your last point:-

It shouldn't make any difference since with very low terminal resistances and adequate conductor size the voltage loss will be minimal. In fact it is desireable to run a charger directly to the battery on both poles. Much simpler, no interference by master switches (& you can still isolate the boats systems and still charge the battery) and less terminals to corrode.

FWIW, I pick up my domestic battery voltage at the output from the diode splitter for my Sterling alternator controller and because I have robust conductors for the <2 metre run to the batery, it works fine.

Steve Cronin




<hr width=100% size=1>The above is, like any other post here, only a personal opinion

 

[VicS]

Re: Catastrophic incident

Here, I think, you may have hit on the possible hazardous scenario.

If such a catastrophic incident occurred, and it could be as simple as a wire breaking due to vibration and touching something it shouldn't or dampness affecting the insulation in a transformer, you could put the 12volt system at 240v relative to earth. In many (most?) cases there will be some sort of path to earth, via the prop shaft perhaps, and the rcd will trip. If there is a flexible coupling cutting out this route, everything is dry and there is no other route to earth , or indeed the rcd fails, you have a situation where the boats 12 system is live!

Then you touch a bit connected to the 12v system with one hand and something connectd to a bit under water with the other (the two halves of the flexible coupling or a bulb holder and a bit of the rig, all of which is "earthed" via the stemhead fitting and the mooring chain) and ***!!!.

Except of course the rcd will trip, or will it? Neither of the two rcds which I have had fail have failed safe. They just failed to trip when they should have.

I know its based on several unlikely events coming together but that surely is the recipie for unforeseen accidents.

Wasn't one of the major rail crashes in the London area a few years ago caused by a loose wire in some signalling equipment making intermittent contact with something?

<hr width=100% size=1><font color=purple>Ne te confundant illegitimi.</font color=purple>

 

[JohnL]

Re: Catastrophic incident

Hi Vic, if a battery charger fails and puts 240v into a 12v battery I would have thought there would be a flash and a large bang but then I am no expert.

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[VicS]

Re: Catastrophic incident

I'm not suggesting that 240v AC is applied across the 12v DC system just that a stray connection could (in very exceptional circumstances) occur between the live side of the mains supply and the 12v system, +ve or -ve, and that if other criteria are met which result in the rcd not tripping then the 12v system is live at 240v relative to the shore earth and the sea.

You've made me think a little more tho' and realise that probably the most likely danger in fact comes from touching the case of an earthed 240v appliance at the same time as any part or the 12v system which could include the outer case of something connected to the -ve.

<hr width=100% size=1><font color=purple>Ne te confundant illegitimi.</font color=purple>