D.C. A.C. Grounds On Steel

[Guest TerryL]

So what are your views on Galvanic Isolators then?

 

The IET wiring regulations state that an earth wire should be continuous without any switching device in it. A semi conductor or diode as is in a galvanic isolator is a switching device. However, they are now permitted if they comply with certain standards of robustness e.g. they must be able to withstand a current of 5000 Amps for the time it takes an RCD to trip three times. Some suppliers are claiming this new standard but they look suspiciously like the old stock! A galvanic isolator does not work as well as an isolation transformer and can easily be switched on, negating the isolation. They can still fail, leaving you with no earth and this is the main problem the Americans have with many claimed deaths attributed.

 

http://www.dairyland.com/media/liability.pdf

[Keeping Up]

A semi conductor or diode as is in a galvanic isolator is a switching device.

I forget the reference now, but I recall seeing it defined earlier this year as NOT being a switching device within the meaning of the Wiring Regulations.

[chris w]

This is about standard electrical safety practice, not something I've made up, why don't you answer my concerns about equipotential bonding if you think I'm wrong instead of just repeating yourself and ignoring the safety aspects that I've highlighted. If you are as clever as you make out then you know I'm right and should be prepared to admit it.

 

You, dear boy, are the one that keeps repeating yourself ad nauseum.

 

If one wants galvanic protection, by utilising an on-board IT, then one cannot earth the input to the hull. If one does, there is no galvanic protection.

 

If the small chance that the input cable may be severed overrides all other considerations in your mind, then an IT is not for you, unless you are going to keep it on shore permanently which is not usually practical. Therefore one would need to utilise a galvanic isolator instead.

 

This is paradoxical because a galvanic isolator overall is not as safe as an IT in that the galvanic isolator could fail open circuit and no earth would exist at all. Much more dangerous.

 

I'll repeat myself.............. there is NO point in having an IT if you earth the shore lead to the hull - the IT is doing nothing for you.

 

My advocacy of hull earthing still stands however and there is no conflict in my views (or Gibbo's). If the IT has one of its outputs earthed to the hull, then any on-board RCD will work perfectly in the event of a fault AND one gets perfect galvanic isolation.

 

Chris

[Guest TerryL]

I forget the reference now, but I recall seeing it defined earlier this year as NOT being a switching device within the meaning of the Wiring Regulations.

 

Yes thanks that's why they are now allowed.

[FORTUNATA]

I guess the debate around that point isn't going to have much impact on myself as my boat doesn't have an isolation transformer. What safety measures older boats do have when plugging into marinas I have no idea as of yet.

What does concern me more is the galvanic isolator which I'll buy in the hope it gives me at least some protection.

 

 

The casing of an IT and how and where it is earthed, has been a topic of debate in many fora, including a number or articles in the excellent magazine Professional Boat Builder. From all the research I have read and "what iffing" the various failure points with the IT, I have concluded that the case should not be earthed at all but completely isolated, effectively achieving a double insulated device, so that if it does become live, it cannot touch any part of the hull. Only the safety screen inside the transformer windings goes to shore earth.

 

The only transformers that, until recently, are potted to achieve this are US ones and pricey. There is now a Brit transformer that should do the job - http://www.airlinktransformers.com/transfo...transformer.asp

 

I have yet to get one, but for the time being my IT is mounted on a wooden plinth and the case does touch any thing else. I think I would be a very strange defect that energises the case without any indicators anywhere else, but a simple neon could be used as a check.

[Chris Pink]

I guess the debate around that point isn't going to have much impact on myself.

 

Well you can't invoke the Ravenous Bugblatter Beast of Traal (as manifested in the linearity of this dimension by an argument on electrical matters on the canal world forum) and then just expect it to go away again quietly.

[Guest]

There's a hole in my bucket,

Dear Liza, dear Liza etc.

Edited October 6, 2008 by Guest

[Guest TerryL]

You, dear boy, are the one that keeps repeating yourself ad nauseum.

 

If one wants galvanic protection, by utilising an on-board IT, then one cannot earth the input to the hull. If one does, there is no galvanic protection.

 

If the small chance that the input cable may be severed overrides all other considerations in your mind, then an IT is not for you, unless you are going to keep it on shore permanently which is not usually practical. Therefore one would need to utilise a galvanic isolator instead.

 

This is paradoxical because a galvanic isolator overall is not as safe as an IT in that the galvanic isolator could fail open circuit and no earth would exist at all. Much more dangerous.

 

I'll repeat myself.............. there is NO point in having an IT if you earth the shore lead to the hull - the IT is doing nothing for you.

 

My advocacy of hull earthing still stands however and there is no conflict in my views (or Gibbo's). If the IT has one of its outputs earthed to the hull, then any on-board RCD will work perfectly in the event of a fault AND one gets perfect galvanic isolation.

 

Chris

 

So what you are admitting is that it is the unacceptable removal of the earth that gives the galvanic isolation, not the onboard isolation transformer. That's what I've been saying!

 

Despite your amateurish or irresponsible comments there is every possibility of an earth fault from any part of an unearthed installation, you can't say there won't be, that's why we always have an earth and there should be absolutely no chance of a dangerous fault anywhere.

 

Amazingly you are suggesting to unsuspecting people it is ok to have a dangerously unearthed boat with the risk of killing people just for the sake of saving a bit of metal. That from someone who claims to be knowledgable I find it quite shocking! You need to get your priorities right, you are also leaving yourself open to legal action if someone takes your advice... and it goes wrong.

 

You're saying a galvanic isolator is not as safe as an IT because it could fail open circuit leaving the boat with no earth and it's dangerous! Well isn't that what you are suggesting by not earthing the boat? You are only looking at the part of the installation fed by the IT, what about the rest that is unearthed?

 

I could suggest that a approved galvanic isolator be used as well for this but then you wouldn't need the IT, or would you? It would give better protection on most of the boat at least without relying on the GI for carrying most onboard fault currents and the GI would not suffer the usual leakage current problems with only the IT connected! A belt and braces approach that can't go wrong and would simplify the IT installation.

 

If this is your final comment or just the extent of your knowledge regarding electrical safety then I can only suggest that for the sake of safety you or anyone else advocating onboard transformers should be ignored and for any installation a knowledgable and qualified electrician or electrical engineer should be consulted and a shore based or inline IT is used or a GI in addition to an IT onboard. I also suggest you Chris go back to your circuit boards and leave installations and electrical safety to the big boys before you get someone killed!

 

No doubt you will want the last word.

[ChrisPy]

There's a hole in my bucket,

Dear Liza, dear Liza etc.

I know an old lady who swallowed a fly .............

[Chris Pink]

You're saying a galvanic isolator is not as safe as an IT because it could fail open circuit leaving the boat with no earth and it's dangerous! Well isn't that what you are suggesting by not earthing the boat? You are only looking at the part of the installation fed by the IT, what about the rest that is unearthed?

 

I could suggest that a approved galvanic isolator be used as well for this but then you wouldn't need the IT, or would you? It would give better protection on most of the boat at least without relying on the GI for carrying most onboard fault currents and the GI would not suffer the usual leakage current problems with only the IT connected! A belt and braces approach that can't go wrong and would simplify the IT installation.

 

What a load of ill-informed twaddle. Have you actually sat down with pencil and paper and worked through your scenarios or done any rudimentary risk assessment of the issues involved?

 

No, of course not, you'd rather just fire off nonsense like the above in some sophistic attempt to be seen as clever.

[Gary Peacock]

What do the regulations say about all this then?

[Guest TerryL]

What a load of ill-informed twaddle. Have you actually sat down with pencil and paper and worked through your scenarios or done any rudimentary risk assessment of the issues involved?

 

No, of course not, you'd rather just fire off nonsense like the above in some sophistic attempt to be seen as clever.

 

Glad to see I still have your attention and negative approval, no please don't reply we know how you will want to highlight the fact that you can't keep up.

[Chris Pink]

What do the regulations say about all this then?

 

the regulations are delightfully vague saying only this;

 

"The neutral conductor shall be grounded (earthed) only at the source of power, i.e. at the onboard generator,

the secondary of the isolation or polarization transformer, or the shore-power connection. The shore-power neutral

shall be grounded through the shore-power cable and shall not be grounded on board the craft. "

 

however this;

 

http://www.energy-solutions.co.uk/dock_power.html

 

as fitted to sea-going yachts and intended to be used a portable interface between the yacht's systems and any old shore power worldwide is fitted in accordance with chris w's understanding.

 

Any other configuration gives no protection whatsoever and negates the whole point of installing an isolation transformer. (draw the diagram Terry L)

 

If you fit the unit on the bank then you protect yourself from the vagaries of the power at that location only.

 

Also it provides no peace of mind as the whole point of an isolation transformer is to give the end-user confidence in the configuration of the 240V power entering the vessel.

[magnetman]

So what you are admitting is that it is the unacceptable removal of the earth that gives the galvanic isolation, not the onboard isolation transformer. That's what I've been saying!

 

Despite your amateurish or irresponsible comments there is every possibility of an earth fault from any part of an unearthed installation, you can't say there won't be, that's why we always have an earth and there should be absolutely no chance of a dangerous fault anywhere.

 

Amazingly you are suggesting to unsuspecting people it is ok to have a dangerously unearthed boat with the risk of killing people just for the sake of saving a bit of metal. That from someone who claims to be knowledgable I find it quite shocking! You need to get your priorities right, you are also leaving yourself open to legal action if someone takes your advice... and it goes wrong.

 

You're saying a galvanic isolator is not as safe as an IT because it could fail open circuit leaving the boat with no earth and it's dangerous! Well isn't that what you are suggesting by not earthing the boat? You are only looking at the part of the installation fed by the IT, what about the rest that is unearthed?

 

I could suggest that a approved galvanic isolator be used as well for this but then you wouldn't need the IT, or would you? It would give better protection on most of the boat at least without relying on the GI for carrying most onboard fault currents and the GI would not suffer the usual leakage current problems with only the IT connected! A belt and braces approach that can't go wrong and would simplify the IT installation.

 

If this is your final comment or just the extent of your knowledge regarding electrical safety then I can only suggest that for the sake of safety you or anyone else advocating onboard transformers should be ignored and for any installation a knowledgable and qualified electrician or electrical engineer should be consulted and a shore based or inline IT is used or a GI in addition to an IT onboard. I also suggest you Chris go back to your circuit boards and leave installations and electrical safety to the big boys before you get someone killed!

 

No doubt you will want the last word.

 

the bit in red - is that true ????

 

just by putting a view on a forum you can get done if some prat thinks you know what you are talking about and injures themselves while following your advice???

 

so I once said you can do locks without using centre lines. if someone attempts to do this and hurts themselves can they sue me

 

surely not... scary.

 

[Scotty]

Despite your amateurish or irresponsible comments there is every possibility of an earth fault from any part of an unearthed installation, you can't say there won't be, that's why we always have an earth and there should be absolutely no chance of a dangerous fault anywhere.

 

Unearthed installation sounds very dramatic

 

I don't have a shoreline on my boat so it is never 'earthed' all mains voltage generated onboard is bonded to the hull and protected by RCD

If I do need a shoreline then I will fit an IT on the boat, the isolated supply will also be bonded to the hull and protected by RCD

[Chris J W]

the bit in red - is that true ????

 

just by putting a view on a forum you can get done if some prat thinks you know what you are talking about and injures themselves while following your advice???

 

so I once said you can do locks without using centre lines. if someone attempts to do this and hurts themselves can they sue me

 

surely not... scary.

 

 

These days ... I'd not be in the slightest bit surprised ...

[Guest TerryL]

the bit in red - is that true ????

 

just by putting a view on a forum you can get done if some prat thinks you know what you are talking about and injures themselves while following your advice???

 

so I once said you can do locks without using centre lines. if someone attempts to do this and hurts themselves can they sue me

 

surely not... scary.

 

 

I think you will find it would come under civil law a "duty of care to others" and in an extreme case, criminal "manslaughter." More likely to succeed if you set yourself up as an expert but anyone can sue anyone for compensation and even if unsuccesful it can be expensive and very stressful. If you are dealing with something that might be potentionally dangerous then unless you're really sure of your ground it is sensible not to give advice that might be acted upon or at least give a disclaimer. Nobody wants to restrict the exchange of information on forums but I do get concerned about the cavalier approach to safety expressed on many subjects and the willingness of some to ram home blatantly dangerous views and misinformation.

[magnetman]

I think you will find it would come under civil law a "duty of care to others" and in an extreme case, criminal "manslaughter." More likely to succeed if you set yourself up as an expert but anyone can sue anyone for compensation and even if unsuccesful it can be expensive and very stressful. If you are dealing with something that might be potentionally dangerous then unless you're really sure of your ground it is sensible not to give advice that might be acted upon or at least give a disclaimer. Nobody wants to restrict the exchange of information on forums but I do get concerned about the cavalier approach to safety expressed on many subjects and the willingness of some to ram home blatantly dangerous views and misinformation.

 

interesting point.

[Chris Pink]

Unearthed installation sounds very dramatic

 

I don't have a shoreline on my boat so it is never 'earthed' all mains voltage generated onboard is bonded to the hull and protected by RCD

If I do need a shoreline then I will fit an IT on the boat, the isolated supply will also be bonded to the hull and protected by RCD

 

Exactly the right way to look at it and a very refreshing cut through of all the waffle and crap spouted on this thread.

 

I think you will find it would come under civil law a "duty of care to others" and in an extreme case, criminal "manslaughter." More likely to succeed if you set yourself up as an expert but anyone can sue anyone for compensation and even if unsuccesful it can be expensive and very stressful. If you are dealing with something that might be potentionally dangerous then unless you're really sure of your ground it is sensible not to give advice that might be acted upon or at least give a disclaimer. Nobody wants to restrict the exchange of information on forums but I do get concerned about the cavalier approach to safety expressed on many subjects and the willingness of some to ram home blatantly dangerous views and misinformation.

 

Another example of the 'i say it so it must be true' form of debate. It is usual and far more helpful to the discussion to back up such assertions with some kind of evidence.

 

If you jump off a cliff you can fly.

 

Go on, sue me.

Edited October 7, 2008 by Chris Pink

[Guest TerryL]

Unearthed installation sounds very dramatic

 

I don't have a shoreline on my boat so it is never 'earthed' all mains voltage generated onboard is bonded to the hull and protected by RCD

If I do need a shoreline then I will fit an IT on the boat, the isolated supply will also be bonded to the hull and protected by RCD

 

Then your boat will be unearthed from the shore supply if it is not connect to it, your risk! It is very dramatic if a fault develops you, your family and friends would be most at risk from electrocution! You could possibly get away with a faulty installation for years but one day the circumstances will change to the wrong conditions and...zap! I've seen it before and nearly lost my brother because the earth was disconnected by a new plastic water pipe and not reinstalled properly. The electricity board engineer who came to fix the line fault said they get a fatality once a week with unearthed installations, is that dramatic enough?

[smileypete]

Then your boat will be unearthed from the shore supply if it is not connect to it, your risk! It is very dramatic if a fault develops you, your family and friends would be most at risk from electrocution! You could possibly get away with a faulty installation for years but one day the circumstances will change to the wrong conditions and...zap! I've seen it before and nearly lost my brother because the earth was disconnected by a new plastic water pipe and not reinstalled properly. The electricity board engineer who came to fix the line fault said they get a fatality once a week with unearthed installations, is that dramatic enough?

 

Dramatic enough, but it sounds like over emotive b***ocks to me:

 

http://www.publications.parliament.uk/pa/c.../61106w0038.htm

 

Fatalities due to home accidents in Great Britain caused by use or misuse of electrical equipment and electrical installations

 

2005-06 (1 April 2005 to 31 March 2006) 13

 

I'm sure the BSS office can give details of any recorded electrocutions on boats.

 

 

Though I agree it's dangerous to have an on board isolation transformer where shoreline protection cannot be guaranteed.

 

The best protection comes from a shoreline RCD, these are not yet a legal requirement AIUI but weatherproof 'inline' types are available.

 

cheers,

Pete.

Edited October 7, 2008 by smileypete

[Chris Pink]

Then your boat will be unearthed from the shore supply if it is not connect to it, your risk! It is very dramatic if a fault develops you, your family and friends would be most at risk from electrocution!

 

It's all very well saying "it is so because i say it so" but i would be interested in your analysis of Scotty's scenario;

 

"I don't have a shoreline on my boat so it is never 'earthed' all mains voltage generated onboard is bonded to the hull and protected by RCD. If I do need a shoreline then I will fit an IT on the boat, the isolated supply will also be bonded to the hull and protected by RCD"

 

How exactly is he at risk? (or his family and friends!!! It's OK for the people he doesn't like very much then?).

 

In what fault conditions would electrocution arise?

[simonk]

You're saying a galvanic isolator is not as safe as an IT because it could fail open circuit leaving the boat with no earth and it's dangerous! Well isn't that what you are suggesting by not earthing the boat? You are only looking at the part of the installation fed by the IT, what about the rest that is unearthed?

 

The rest is ISOLATED from the shorepower, and it has its own independent earth by connecting one of the outputs to the hull. That is, a fault in the wiring 'dowstream' of the isolation transformer will be dealt with just as safely as any other earthed installation. Simply not earthing the boat installation at all is very different, and not what anyone is recommending.

[chris w]

I think you will find it would come under civil law a "duty of care to others" and in an extreme case, criminal "manslaughter." More likely to succeed if you set yourself up as an expert but anyone can sue anyone for compensation and even if unsuccesful it can be expensive and very stressful. If you are dealing with something that might be potentionally dangerous then unless you're really sure of your ground it is sensible not to give advice that might be acted upon or at least give a disclaimer. Nobody wants to restrict the exchange of information on forums but I do get concerned about the cavalier approach to safety expressed on many subjects and the willingness of some to ram home blatantly dangerous views and misinformation.

 

Not only do you not know about electrics, but you are also ignorant of the law, whereas I have studied both.

 

In order to bring a suit against another person for negligence you have to prove ALL of the following:

 

1. They owe you a duty of care (see below for definition)

 

2. They breached that duty of care

 

3. You suffered damage as a result of the breach

 

 

To show that a duty of care exists the person giving the advice has to fulfill ALL of the following:

 

1. They are acting in their professional capacity when giving the advice

 

2. You were asking for and received their professional advice

 

3. It would be reasonable to assume that you would act on the advice or information given

 

So, unless all of the above transpired, then a negligence suit would fail. The info given is an "opinion" and not professional advice.

 

Chris

[carlt]

interesting point.

Despite being wrong.

 

The advice given on this forum is quite clearly described, by Jon, as the advice of amateur boating enthusiasts, even if that amateur advice is given by someone with a great deal of professional experience.