Shore Power Installation

[aledlgriffith]

I want to install 240v Shore power to my yacht this winter so I can use 240v supply that is available in our compound. I intend using a garage consumer unit with RCD and mcd's, surface mount external connector and suitable weatherproof connectors and cables.

I have read on some forums that the internal 240V circuit should be earthed to the engine block. Is this necessary can I not ensure that the earth connectivity is maintatined back to the earth connection of the incomming feed?

 

[sailorman]

I want to install 240v Shore power to my yacht this winter so I can use 240v supply that is available in our compound. I intend using a garage consumer unit with RCD and mcd's, surface mount external connector and suitable weatherproof connectors and cables.

I have read on some forums that the internal 240V circuit should be earthed to the engine block. Is this necessary can I not ensure that the earth connectivity is maintatined back to the earth connection of the incomming feed?

do NOT earth to engine OR 12v system in any way .
keep the 240v totally seperate. i have the set-up you propose to do,get a good quality external plug & socket for the connection to the boat. mine is marketed by Index marine ( French made )

 

[markdj]

As long as you have an RCD which you already mention you are going to fit or an isolation transformer, then you do not need to connect the AC earth to the DC earth, grounding or anode connections.

Mark
www.boatdoctorni.com

 

[cozzykim]

You can treat your boat like a tent!! Supply it as you more or less suggest, with a system commonly referred to as an "electric hook up" by the camping/caravanning brotherhood. Parts can be readily obtained from Go Outdoors or similar.

If you use the "hook up" principle then the 12V and 240V systems are by their nature totally separate as the hook up is not part of the boat's electrical system, it remains part of the building's system.

As long as the "shoreside" outlet is of the correct type (water/tamperproof), with an RCD supplying it then it will be fine.
Any 13A socket outlets must have connected and checked earths, whether they are mounted on the "hook up" outlet panel or (if you decide to have a dedicated shore power system) built into the boat's structure.

All 240V appliances must either be double insulated or have earth connected (and preferably PATested if you don't know their source/history).

 

[VicS]

Opinion is very divided about this.

Some, like Sailorman, say do not connect the earth others say to maintain full safety the shorepower earth should be bonded to the boat's earth system (That usually means the DC negative, engine block, anodes etc but should include all major metal strucures.)

ISO 13297 (Small craft — Electrical systems —Alternating current installations) says that the earth need no be connected to the ships earth provided there is an RCD protecting the whole craft.

Other standards including the American Boat and Yacht Council (ABYC) and I believe European standards do require the ships earth and shore power earth to be bonded.

The snag with bonding the two together is galvanic corrosion caused by small currents conducted by the shorepower earth then meaning that a galvanic isolator becomes necessary if shorepower is left connected (but not necessarily in use)

A few months ago I had a long and public discussion with James Hortop of Merlin Powerstore about this which it should be possible to find with the search function.

One interesting point he made was that he expected the next revision of ISO 13297 to be changed, bringing it in line with other standards.

At the end of the day I think your choice.

Opt for not interconnecting the two as allowed by the current ISO 13297, ignoring the advice of expert Electrical Engineers and maybe accepting a very small reduction in safety or bond the two as other standards, and probably the next revision of ISO 13297, require and experts in the field advise but then add a Galvanic isolator to guard against galvanic corrosion.

If you want the maximum level of electrical safety (without using an isolating transformer) then bonding is probably the way to go. If you are not fussed then don't bother.

 

[VicS]

Nigel Calder is the acknowledged expert, his book is almost always the most highly recommended.

Therefore anyone who enjoys some serious reading might like to read his article in a recent edition of Proboat Magazine. Spanning pages 61 and 62 you will find his explanation of why the AC earth should be bonded to the DC negative etc.

http://www.proboat-digital.com/proboat/200604/

Note that he is a member of the ABYC's Electrical Project Technical Committee so it is not surprising that his views are in line with the ABYC standards!

 

[aledlgriffith]

Thanks to everyone who responded I think I will go with the option of not connecting to the negative/block.

 

[VicS]

I think I will go with the option of not connecting to the negative/block

Make sure your RCD is working and make sure that the incoming AC supply is well separated from the DC and any metal structures then you should be safe.

Remember though despite being in accordance with the current version of ISO13297 it is contrary to the advice of the acknowledged experts in the field anf other standards. It's those acknowledged experts the prosecution will call as witnesses in court!

 

[markleuty]

The comments above are about 240v and 12v being completely separate.

Is this still the case if a battery charger is installed, or is the electronics in the charger sufficient separation?

Mark

 

[VicS]

A battery charger should not interconnect the AC 240 volt supply with the DC 12 volt supply but it is a bit of equipment that could develop a fault, unlikely but could, and put the whole DC 12 volt system at 240 volts.

If the DC system is earthed then the RCD will trip or even if the RCD fails the fuse will blow or mcb trip.

If the DC system is not earthed then none of the protection devices will operate until some unfortunate individual completes the circuit. Hopefully they are saved from electrocution by the RCD but if that fails ...... **!

In reality of course there will almost certainly be other routes by which the circuit to earth is completed, via the engine and the stern gear for example so the RCD will probably trip any way but you cannot rely on that.

Provided the craft is fully protected by an RCD the risks are small, they can be reduced further by earthing the ships earth/DC negative, reduced even further by using an isolating transformer, preferably pontoon mounted but they can only be eliminated by not having mains power aboard at all.

 

[cozzykim]

Agree with all VicS says, it depends on how many eventualities you feel you need to cover.

The "caravan hook up" is fine for operating tools etc. but I might consider connecting 12/240 grounds if leaving chargers etc. unattended for any length of time or if someone is working on the boat who is not au fait with the principles.

There may be other considerations if anyone not yourself or immediate family is put at risk (however small), you may require self certification in that case.

It depends how the regs are interpreted.

EDIT: An RCD is really reassuring, theoretically if there isn't enough leakage current (through you ) to trip it, then there isn't enough to kill you.

 

[Boomshanka]

Caravanners are our friends when looking for power products (without a 'marine' mark up)

 

[VicS]

An RCD is really reassuring

The trouble is that I have had 2 (maybe 3 ) fail and they did not fail safe. They failed to be permanently ON. Admittedly they were the plug in types but it destroys ones faith in such devices.

 

[cozzykim]

The trouble is that I have had 2 (maybe 3 ) fail and they did not fail safe. They failed to be permanently ON. Admittedly they were the plug in types but it destroys ones faith in such devices.

Hmmm, a 5 quid plug in'er maybe, I'd be shocked ( ) if a consumer unit RCD device as suggested by the OP failed closed though.

 

[Gumpy]

Hmmm, a 5 quid plug in'er maybe, I'd be shocked ( ) if a consumer unit RCD device as suggested by the OP failed closed though.

No they tend to fail in a worse way.
They still respond to the test button but if tested with a proper RCD tester fail to operate.
I see one or two a month fail out of a total stock of between 1000 and 1500 out on the road at any one time.
The moral is if you use RCD get them tested with a proper tester.

 

[mikehibb]

Check out the IET Wiring Matters site,

Issue 29 has a pdf for Houseboats and recreational craft

Issue 23 has a pdf for Marinas and similar loactions

Sorry can not link to the pdfs directly, but can be found below:

http://www.theiet.org/publishing/wiring-regulations/mag/

You will need to click on 2007 section to find issue 23.

 

[VicS]

They still respond to the test button but if tested with a proper RCD tester fail to operate

Out of interest what does the "proper tester" do that the test button does not. I always assumed that either just simulated a leakage to earth of a magnitude (30mA ?) that should initiate a trip.

 

[Gumpy]

Out of interest what does the "proper tester" do that the test button does not. I always assumed that either just simulated a leakage to earth of a magnitude (30mA ?) that should initiate a trip.

The tester we use tests at half the trip value then we test at the trip value and it gives us a time reading as to how long it takes to trip.
Most failures just don't trip, some trip but take to long.
Depending on manufacturer ( and I cant remember which is which) the trip button does not always simulate a leakage to earth but just energies the trip mechanism......... telling you that the trip mechanism works but little else.

 

[DaveS]

Depending on manufacturer ( and I cant remember which is which) the trip button does not always simulate a leakage to earth but just energies the trip mechanism......... telling you that the trip mechanism works but little else.

This is entering a completely different, and rather worrying, territory.

Operation of a RCD test button should create a leakage current which, if the RCD is operating correctly, should trip the breaker, and I would expect any reputable manufacturer's products to behave in this way. (Some manufacturers even helpfully print a circuit diagram showing these internals on the breaker case.) I'm also fairly sure this is covered by ISO specs, but haven't the time to look it up. However, we then get into the issue of counterfeit goods and dodgy imports...

A couple of years ago the electrical trade press published pictures of overcurrent circuit breakers which, internally, were actually isolating switches, i.e. they provided no overcurrent protection whatsoever. They were crude fakes of a reputable brand. Beware of "bargains" which could cost your life ...

 

[VicS]

The tester we use tests at half the trip value then we test at the trip value and it gives us a time reading as to how long it takes to trip.
Most failures just don't trip, some trip but take to long.

Thanks for that. More or less as I expected but did not know.