Installing Shore Power

B

BrendanChandler

Well-Known Member
Joined
4 Feb 2003
Messages
352
Location
UK
www.brendanchandleryachtdelivery.co.uk
My boat is currently fitted with a Merlin Mains Charger. The input is a 3 pin plug which is connected to a socket on the end of a shore power cable. I wish to install a couple of sockets and propose the following installation.
A standard 3 pin socket on the end of the shore cable.
The onboard installation to consist of:
A 3 pin plug to be connected to the socket.
The earth from this to be passed through a Galvanic Isolator on route to a twin trip switch.
The output from the trip switches to be send a) to the Mains Charger and b) to a single cable which will feed 2 or possibly 3 sockets.

Should I take the Earth from the Galvanic Isolator also to the engine ?

Any comments or suggestions would be very welcome. The life you save might be mine.

Brendan

<hr width=100% size=1>
http://hometown.aol.co.uk/brendanchandler/index.html
 
Sounds a little scary to me -- by standard three pin I hope you don't mean domestic 13 amp three pin plug/socket on your connection between shorepower and vessel.

You need to fit a proper outdoor/marine/caravan type inlet on the outside of your boat.

This should then be connected to a consumer unit comprising an RCD and a number of MCBs. In your case two would be enough.

From the MCB you can then run to domestic outlets. I have my charger on dedicated MCB, I have my immersion on a second then two ring mains, one for the galley, where we have two 2 way outlets for microwave, kettle and toaster, and a second that supplies 4 2 way outlets for TV, radio, tools etc.

Some places sell kits, Seamark Nunn is example, but you can go along to your local B&Q and pick up a small unit and all the bits for under £70.

Most importantly, if you are not cofident of doing the job yoourself, get someone who is qualifies, or at least get the installation checked by someone who is.

To be honest it's not that hard a job, just be meticulous about your connections!


<hr width=100% size=1>
 
Trevethan,

This is of interest to me too - where do you earth if you don't have an inboard engine?

Alisdair

<hr width=100% size=1>"so long as all you want is a penguin’s egg"
 
An RCB protects by detecting a difference in current out and current back, the conclusion being that if they are not equal, the difference has gone elswhere. If "elswhere" is you, the consequent disconnection is supposed to save your life. 30mS disconnection time has been decreed as sufficiently short to not stop your heart.

On a boat, the earth is a very different matter. If the structure is steel, the disconnection philosophy may hold true but with a grp or wooden hull the situation could be vastly different. A wet wooden hull may be conductive, a grp hull probably isn't. However, if the occupants are insulated from the shoreside earth, any leakage into the body probably won't go through it anyway.

One remaining benefitof fitting an RCB is that if connected appliances develop a short between the supply (either live or neutral), that will trip the supply. This has got to be good.

<hr width=100% size=1>GBW
 
The earth returns to the bollard -- some people say you should bond your AC earth and your dc earth (the ac also earths back to teh power station via the bollard.

I haven't done so on the majority of forum advice. And my system works -- I used to have an oil filled radiator which shorted. pop when the mcb and rcd -- tooka while to isolate the fault, but once unplugged, all perfect - no harm to anyone.



<hr width=100% size=1>
 
Thanks for the responses.

At the risk of displaying my ignorance for all to see, can I ask a few idiot questions please.

"You need to fit a proper outdoor/marine/caravan type inlet on the outside of your boat".
From a safety point of view, how does drilling a hole in the hull help? The cable currently leaves the boat through a sheltered port under the hood and terminates in a domestic type 3 pin socket in the centre of the cable drum.
If the short cable from the plug that takes the power from the Shore Cable is correctly treated by feeding through RCD, Galvanic Isolator and then MCB (presumably this is a trip switch) all should be well.
I believe that I can buy an RCD which plugs into the end of the shore power lead so that protection begins there.

Do I need ring main for 2/3 sockets?

Should the outlet of the Galvanic Isolator go to both the engine block and the earth for the AC system?

Is there anything special about the connections required?

I will take your advice about having the installation cheked out when complete.

I am very grateful for advice and comments.

Brendan


<hr width=100% size=1>
http://hometown.aol.co.uk/brendanchandler/index.html
 
<"You need to fit a proper outdoor/marine/caravan type inlet on the outside of your boat".
From a safety point of view, how does drilling a hole in the hull help? The cable currently leaves the boat through a sheltered port under the hood and terminates in a domestic type 3 pin socket in the centre of the cable drum.

Go to your local caravan dealers and aks for :

a) Exterior block mount socket
b) Plug to fit above ...... or even better - get a ready made-up caravan lead in length needed ... 10, 15, 25m etc.

The exterior block socket is fitted somewhere handy with socket entry facing down. The hole drilled through cockpit bulkhead or whatever is behind the block and effectively sealed. It is NOT through the hull........ common places are forward end of cockpit bulkhead, aft cockpit bulkhead etc. ..... anywhere where its clearly visible and not fogotten when unberthing !, also semi-protected from weather.

You may be advised the buy some expensive plug / socket etc. but believe me the average caravan owner treats his plug and socket similar to any boatie and mine have lasted years ....

The lead from the block then runs supported to the Breaker box you fit in the boat.

If you enviasge using some reasonable powered tools etc. ..... actually you'll find that 10 or 15Amps is max allowed on shore line ... a ring-main may be advised. I have 2 mains sockets in my boat and I have single but thick cable to take the load, not a ring. This goes through a single breaker. The second breaker is going to either sort charger or if I fit extra mains powered lights.

Simple but effective. As others - I have no earth to engine or couple with DC earth .... it is isolated. I bought a number of books and trawled through them .. and couldn't actually get a final single conclusion about this .... that also includes the PBO Mag's articles about this a couple of years ago.
All the books illustrated the possibility of elctrocuting swimmers, induced corrosion, all sorts of things with each version of wiring !! So now I decided stupidly to trust ...a) RCD, b) Marina breaker.

Now here comes the shite ftom others about how wrong I am .....


<hr width=100% size=1>http://groups.yahoo.com/group/gps-navigator/
 
I can't comment on the galvanic isolator.

Also if you carry out the install as you described and have it checked no electrician worth his salt would agree and it would fail the Boat Safety scheme -- it's sounds a bit heath robinson. With electrics its best to follow the standard methodology.

The outdoor inlet is not just a hole in the boat to stuff your lead through. it is a special weather resistant socket fixed on the outside of your boat. a cable then links it to the consumer unit with the RCD and MCBs.

Your shore power cable should be good quality (arctic) cable of sufficient thickness to carry a load along its length with limited volatage drop between the stanchion and your power inlet.

I have two leads, each a little longer than the boat and can join them if I need to run fron a distant power stanchion.

What you suggest is little more than the extension cable through the hatch, which is not suitable for a permanent installation in my view. It leaves you entirely reliant on the marina supply being properly set up and in full working order.

By introducing a consumer unit you protect yourself to a certain degree from faulty equpment at the supply side.

Boats, being generally damp, vibrationy places need a proper safe installation.

Maybe you should seek advice from your insurers. If they are happy with your proposal, go with it. But from your description, it sounds less than safe.

Also, if you use the vessel on British Waterways canals/rivers, it will not meet the BSS.

The seamark nunn kit costs £87 -- and includes instructions

http://www.seamarknunn.co.uk/catalog/items/item988.htm

best of luck!

Nick


<hr width=100% size=1>
 
Hi Nigel,
As you can tell from the simplicity of my questions, I am a novice in this field.

I have suffered from de-zincification of my prop in the last year since I moved into a marina and I have trawled the internet for information. I show below a few extracts from info received, including a paragraph from West Marine. They seem to suggest that Galvanic Isolators are compulsory to comply with US safety codes.

I take your poinnt about the caravan equipment and will look into that. I have a problem in finding a suitable location where I can avoid a long length of mains cable before it gets to the RCD, Galvanic Isolator and Trip Switches. The side wall of the main locker in the cockpit might be possible.

Thanks again for patience but I have to start from my current position of ignorance.

Brendan

EXTRACTS FROM ARTICLES ON GALVANIC ISOLATORS:
The purpose is to disconnect your wet metal parts from the dock supply in order to prevent electrolysis. The trouble is, however, you need them connected together so that if there is an electrical short on the boat, it doesn't make the boat alive at 120 volts or worse which can give you quite a kick when you step off an aluminum dock!!
Stray, low voltage current flowing between the AC safety ground and DC bonding system is a principal cause of this "galvanic" action. This type of stray current will normally overload your zinc anodes as they try to protect other near by boats and/or metal objects of the marina.
Installing the Galvanic Isolator between the AC safety ground and DC bonding system (see diagram), blocks a majority of the low voltage currents and corrosive action on your zincs is significantly reduced ( while the integrity of the critical safety ground path is maintained.) This means a significant savings in boat haul-out fees and zinc replacement costs.
Galvanic isolators connect to the green wire, close to the shore-power inlet. Simply put, isolators block the circuit of galvanic current flow between neighboring boats. Isolators contain diodes, which are like valves whose inherent resistance blocks the low DC voltage generated by galvanic activity (up to 1.0 volt), but which conduct higher voltages exceeding the initial resistance. The idea is that your boat becomes isolated from passing or receiving low-voltage galvanic current between neighboring boats while still being able to pass dangerous AC voltage through the green wire to the shore ground.

What is a galvanic isolator and why should my shore power system have one?
A galvanic isolator is a device used to block low voltage DC currents coming on board your boat on the shore power ground wire. These currents could cause corrosion to your underwater metals; through hulls, propeller, shaft etc.
Boats in a marina plugged into shore power all act as a giant battery. They are all connected together by the green shore power ground wire, which is (or should be) connected to their DC grounds, engine block, and bonded underwater metals. (Required by ABYC E8 8.5.3) If the boats are in salt water then that forms an electrolyte and the dissimilar metals connected together act as a battery, causing corrosion.
When a vessel is connected to a mains (230v AC) shore supply, the earth conductor should be taken to the same single earth point on the hull as the DC negative. The other end of the earth conductor is taken, via the generating companies distribution grid, to a sub-station where it is physically bonded down to planet earth. If a second vessel is then connected to the shore mains supply adjacent to the first vessel, a circuit exists between the two vessels via the common earth connection to the sub-station and through conductive water.

Alternatively, if the vessel connected to the shore mains supply is adjacent to a metal object (ie a jetty) that is driven to planet earth, again a circuit has been completed. If the potential between the two vessels or one vessel and the jetty is slightly different, a current will flow and corrosion can occur. This is galvanic corrosion. This type of corrosion can be prevented by fitting an isolation transformer in the mains supply immediately after the input plug on the vessel. Alternatively, a galvanic isolator can be fitted in series with the AC earth conductor to block low voltage DC galvanic current flow, whilst permitting the passage of alternating current associated with the earth conductor.

See Practical Sailor August 15, 1995 for a detailed treatment of the green wire. The best solution is a heavy and expensive isolation transformer. The acceptable solution (for the rest of us) is to install a light and inexpensive Galvanic Isolator in the green wire, between the shorepower cord socket on your boat, and the connection to the boat's AC panel. Then, connect the grounding conductor (green) of the AC panel directly to the engine negative terminal or its bus. Note that this meets ABYC's recommendations. In choosing Galvanic Isolators, make sure that you select one that has a continuous current rating that is at least 135% the current rating on the circuit breaker on your dock box. Certain Galvanic Isolators (e.g. Quicksilver) include large capacitors in parallel with the isolation diodes, which in certain situations theoretically provide better galvanic protection. Unfortunately, these units cost substantially more than conventional Galvanic Isolators. If you feel like spending real money on galvanic isolation, you might as well do it right and buy an isolation transformer.


<hr width=100% size=1>
http://hometown.aol.co.uk/brendanchandler/index.html
 
This is also of interest to me. Without distrating from Brendans post, should we have a galvanic isolator? We are steel, with a bipolar isolated perkins and thus no earthing to the hull. i have asked Mr. Sterling, but he did not answer this Q.

How do you choose the correct RCB, is it based on the size of the batt. charger, or should it be on the max. total usage that one may use at any time on the AC system?

tks

<hr width=100% size=1>
 
Hi Jambaman,
The following was culled from one of the extracts I mentioned.

It refers to Galvanic Isolators but may be applicable to RCDs.

In choosing Galvanic Isolators, make sure that you select one that has a continuous current rating that is at least 135% the current rating on the circuit breaker on your dock box.

It does not say how to find the current rating on the circuit breaker on the dock box.

Brendan

<hr width=100% size=1>
http://hometown.aol.co.uk/brendanchandler/index.html
 
thanks brendan, bloody marvelous info. But what i can't determine is whether we should have one on Ouma as we have no grounding, and thus stray currents should (in theory) not effect the electrical system. Is this crap, should we have a GI regardless?
cheers

<hr width=100% size=1>
 
thanks brendan, bloody marvelous info. But what i can't determine is whether we should have one on Ouma as we have no grounding, and thus stray currents should (in theory) not effect the electrical system. Is this crap, should we have a GI regardless?
cheers

<hr width=100% size=1>
 
Hi,
I am really not qualified to judge but a couple of thoughts are
The engine block is probably earthed to enable the 12v system to start the engine, provide an earth for the alternator etc.
If that is true and the propshaft is not insulated from the engine, it is in contact with the sea water and a galvanic cell could be set up with other boats, the pontoon etc etc ?

If the 220v were to make the engine live, then there ought to be an earth circuit back to the shore earth? - hence need for Galvanic Isolator.

This reply is really more an agenda for other wiser folk to comment on.

Brendan

<hr width=100% size=1>
http://hometown.aol.co.uk/brendanchandler/index.html
 
I am no expert ....

Far far from it .....in fact the marina electrician when he disconnected my electrics for changing engine with engineer .... said that my old system would not be reconnected ..... if I wanted he would wire properly / advise me on what to do. Having already spent a fortune I took his advise on parts.
Galvanic Isolator was not mentioned ......

OK - the installation I have - I have plans to alter slightly .... put more sensitive breakers in etc. Add more services via the second breaker ....... but isolation is purely by not connecting earths etc in the boat to engine etc.
I have anodes - but they are lasting quite well - with no signs of prop wastage etc.
The only connection between 240V and 12V systems is the float charger on the batterys. This due to the transformer / rectifier etc. does not directly link them anyway ..... thats how I understand it anyway ....

One day - I will know the answers ..... but today like others - still learning.


<hr width=100% size=1>http://groups.yahoo.com/group/gps-navigator/
 
Re: I am no expert ....

If you bond to the hull on a steel boat/ Hull then you must fit a galvanic isolator to protect yourself from stray currants created by the shorepower supply and other boats and metal objects near to your hull.
By connecting to the hull you are setting up a circuit via the water the boat is sitting in so fit an isolator. Simple
Try also not to moor near to other steel vessels and metal walkways etc.
I have seen five year old canal boats kept in marinas with 5mm pits all over them caused by galvanic action from stray currants.
If you dont bond to the hull then you should still fit the isolator as a precaution.
They are not expensive after all.
Also if you dont bond to the hull then the RCD will not work as well due to having to trip back all the way to the shorepower supplies earth point (which could be a long way away or worse poor due to other problems).
You can help this problem by fitting an extra earth spike hammered in to the bank near to your supply box connected to the marinas earth lead.
This is generally not allowed or not possible though.
One problemis that if you have the system fitted by an electrician then he will insist on earthing to the hull or a through hull fitting as this is what is specified in the regs for the rcd to work well.
If you have a steel boat then you take your choice.
These points apply to glass and wood boats as well.
If you want your RCD to work well then it must have a short good earth point.
Allways get an electrician to check out or fit the system for you if in any doubts.
Also make sure that the shore power to boat socket is of a good quality.
There are better ones available than the ones you get in marinas ans caravan shops that really are waterproof.
If you do fit it yourself make sure the socket on the boat has the male or pins and that the end of the shore lead is the female ie no pins showing when disconnected.


Joe




<hr width=100% size=1>
 
I am going to look at galvanic isolation, but not being steel and not having bonded earths, I didn't sorted it out just yet.

Regarding the RCD I took advice from an electrician and got the most sensitive one I could find -- This should also warn me of current leakage.




<hr width=100% size=1>
 
Re: I am no expert ....

Thanks for that Joe,
I am gradually getting the picture.
Presumably the first item on the boat after the shore power connection is the Galvanic Isolator where the input is the Earth from the shore power and the outputs are a) earth to the engine block and b) earth to continue to RCD, Circuit Brekaers and the rest of the installation?

Brendan

<hr width=100% size=1>
http://hometown.aol.co.uk/brendanchandler/index.html
 
Re: I am no expert ....

Hi Brendon,
No i would not connect to the engine block with the mains earth supply. If you are going to connect to the hull or in outher words a ground for the RCD then i would go through a seperate through hull skin fitting isolated away from the 12 volt systems.
This should help to prevent a massive overload on the 12 volt systems in the event of a short to earth from the 240 volt.
Yes the galvanic isolator is connected in the earth line before it passes through the contact breaker board. But this may vary depending on the type of isolator you fit. Instructions will come with the isolator.
Joe



<hr width=100% size=1>
 
Re: I am no expert ....

Hi Joe,
Thanks for that.
I thought that the Galvanic Isolator was designed to connect the boat earth with the AC earth but with diodes blocking the small voltages.

So, my guess was that if connected the earth imerging from the Galvanic Isolator and sent one connection to the RCD, it would have it's route to earth and the second to DC Earth it would also have its route to Earth through the diodes.

Any comments on that would be welcome.

I expect that when I buy the Isolator it will come with instructions but I was trying to understand the whole process before starting.

Brendan

<hr width=100% size=1>
http://hometown.aol.co.uk/brendanchandler/index.html
 
You must log in or register to reply here.

Other threads that may be of interest

PabloPicasso
Mains power
2 3
Replies
44
Views
779
PaulRainbow
PaulRainbow
D
Galvanic Isolator location
Replies
5
Views
303
Alex_Blackwood
Alex_Blackwood

Share this page

Top