Long Term Use of Shore Power

N

nightjar

Well-Known Member
Joined
26 Jun 2004
Messages
595
Visit site
I have just replaced some skin fittings that were showing signs of dezincification (pinking). I suspect this is the result of using a tube heater through the winter that has been plugged into a 240V socket; one of 3 fitted by the boatbuilder. The shore power is left connected through the winter months and I have read on the forum that the earth wire links all the boats together to form a nice big battery. Can I avoid the problem this causes by using a stand alone power supply direct to the tube heater and not using the boats mains wiring ?
 
Do you have a galvanic isolator?
As to the wisdom of a stand-alone power supply to the heater, you'll no doubt get other posts from members wiser than me in electrical affairs, but I expect they'll ask how the current's supposed to get to earth if there's a fault. I think it's a 'no' on that one.
 
No I don't have a galvanic isolator....still unsure if they are a good idea or not. With regard to a stand alone power cable to the heater, it would be earthed through the 3 pin plug or am I missing something ?
 
Galvanic isolator is the answer. I have one plus an extra anode dunked over the side and wired back to the one already bolted on.

Can't say if the extra anode works or not as I'm still in the water, but it sure aint doing any harm.

Once you've fitted the isolator, then you will not have to worry about safety issues.
 
I thought like you, then somebody kindly posted this link

http://www.galvanicisolators.com/

on one of the pages it explains that connecting to the shorepower earth is the problem since it links all nearby boats together as they are linked to the same earth and your metal bits are sitting in the same electrolyte (the water). Hence the electrolytic action.
 
If your boat has a conventional shaft and "P" bracket set-up then I'm sure that you will find that the "P" bracket is also a victim of de-zincification.

Apart from having the shaft held in place by only a thin fin of granular, very soft copper, you'll find that when it comes to replacing the cutless bearing, the grub screws will just strip the threads of their holes when you try to tighten them.

Then at pre-sale survey time the surveyor is bound to report that the "P" bracket is unsafe.

As to the advisability of a galvanic isolator, I would ask you to ponder as to why their alternative name is "Zinc Saver"?

if it were my boat (& mine IS constantly connected to shorepower with no ill effects) i would replace all affected parts AND fit a GI without further delay.

Steve Cronin
 
Er . . . .

Where do we differ? Galvanic isolator is the essential bit of kit when connected to shore power as outlined on the website.

I only have additional "dangly" anode as the one on the boat is a bit worn and I'm in close proximity to additional steel bits on the pontoon, plus a steel boat close by.
 
I think the something you're missing is: what if the fault that develops is in the shore earth? Then you don't have an earth at all.

Incidentally, if you baulk at the cost of an isolator (around £80), feel free to PM me and I can send instructions for a DIY one. (I'd post the link for it, but it seems no longer to work).
 
[ QUOTE ]
Can I avoid the problem this causes by using a stand alone power supply direct to the tube heater and not using the boats mains wiring ?

[/ QUOTE ]

Lets' get back to the original question.

I see no problem in running a seperate mains lead, from an RCD at the shore end, to the boat, and running a heater - or anything else - from it.

Why would he need a galvanic isolator in this case? Yes, probably if he wants to use the boats mains wiring.

The lead is isolated from the boat, and the user is protected by the RCD - of whatever type, wired or plug-in.
 
If the shore earth fails then surely the situation is the same with or without a galvanic isolator. Remove the earth and no galvanic activity; just the risk of electrocution. When I was in Southern Ireland in the '50 the 220V mains in houses had no earth, just 2 pin plugs !
From all the advice posted on this I think that :
1. Ideal solution is to fit a galvanic isolator so that SWIMBO can continue to use her hair drier from the boat 240V plugs.
2. As a temporary measure pending the isolator, only heat the boat using a stand alone connection to the heater. Hope I have got this right ! Thanks to all and have a good sailing season.
 
The marina supply may have a leak....

It may be nothing at all to do with your own installation. It may be that there is a fault on the pontoons letting power leak into the water. I don't believe that any galvanic isolator will help you there. Find out if others round you have had the same problem.

Not sure how you can check this out - but the marina will totally deny any problem!!
 
Re: The marina supply may have a leak....

If the earth on board is not connected to the anode or skin fittings it cannot be part of the "battery" ... but then you rely on the supplies earth..
 
Just to make sure you understand what a Galvanic Isolator does......
The installed mains wiring system of the boat may include a connection from mains earth to the negative of the engine and earth wiring connecting anodes etc.(ships earth) for safety. If your mains earth is connected to the ships earth then this can cause troubles from leakage current.
A GI is fitted into this earth wire and will not allow leakage currents to pass although any real voltage (current) as in a fault situation will pass. So questions of fitting a GI are not applicable unless you have a connection of mains earth to ships earth. Beware of any mains operated device which has a metal body which is connected to the mains earth. If the body is also connected to the ships earth (a battery charger is a classic) or your hot water system if the tank connects to the ships earth then that would bypass any GI anyway.
So you should use a multimeter on ohms scale to check to see if you have a connection mains earth to ships earth. (With mains plug removed.)
Unfortunately your corrosion symptoms may or may not be caused by mains earth and it will take another year or more to prove if you have fixed the problem. good luck olewill
 
William, your post has thrown me a little into confusion. Can you clarify this for me please. If the shorepower is not earthed/connected to the ships earth is a GI necessary? The link I posted suggests it is. I was going to connect up the immersion and battery charger earth solely to the RCB/MCB and put a GI 'in line' between the shorepower connector earth and the RCB/MCB as per the diagram on the help page on the link and have no link to the ships earth (which is the battery/engine block). I follow entirely what a GI does; it's this linkage of mains earth that seems confusing.
 
Olewill,

Quote Adverc installation instructions:
Mount the Galvanic Isolator adjacent to the AC distribution panel.

Connect the incoming shore mains earth cable to either terminal on the Galvanic Isolator. Ensure that this connection is the only one made in the shore mains earth line and comes directly form the bulkhead input plug.

Connect the other terminal on the Galvanic Isolator to the earth buss of the AC distribution panel and from there to the common DC negative / earth stud on the hull.

The Isolator can be routinely tested, using a multimeter on a high resistance setting (k ohms). Probing the two terminals in either direction, should indicate approximately equal values.
End quote

These installation instructions describe a connection to boat earth stud. Excuse my ignorance but is this the hull anode or the 12V DC Negative. Your note suggests that such a connection will bypass the GI. Other installation instructions only describe connecting the GI in series with the shore mains earth wire. Sorry to display my ignorance on this subject but I am unsure what the GI should be connected to; AC earth only or AC earth and DC earth.
 
It's quite simple really. The earth lead coming on board from the shore supply is connected to one side of the galvanic isolator. The other side of the GI goes to the boat's earth bus-bar. This should be connected to the anode, battery negative and also the 240volt socket earth and anything else that is earthed.

No other connection to the GI is required
 
Umm, ok thanks. And the need to connect to the anode with the 240 system is solely as a failsafe in case the shorepower earth fails? Must the 12v system be linked in as well? Sorry for the additional questions. Since I have no galvanic action at present, I'm about to do without the immersion. Grateful for anything further.
 
It depends very much on the wiring of the boat. I understand that some builders go to some trouble to isolate the -ve battery from the ships earth. ie water and anodes. This however usually requires insulation of the prop shaft from the engine or insulation of the electrical -ve from the engine block. I think however that most boats accept and have the -ve connected to the anode prop shaft and water earth so you have no choice.
So if you have simple 240vAC system that is isolated to the mains wiring only and rely on the dock earth then the earth wire is not connected to the ships earth. But if it is a sophisicated system and the mains is connected to the ships earth then a GI should be fitted between them. And......... make sure that none of you appliances particularly battery charger connects the mains earth to the ships earth via pipes or wiring.
olewill
 
You must log in or register to reply here.

Share this page

Top