Hull Earth Bond

[Keith M]

 

However, it also very much depends on which GI you were testing (See post 50). I had a lot more than 4 appliances connected when I did my test and could not force the GI to conduct. This was the Safeshore 70amp GI with status monitor. Which make and model of GI were you testing?

 

Firstly I have to assume that you are happy to except that a GI is a electrical switch

 

What I am a little concerned about is that if your GI would not start to conduct then how was all the current going back to earth this must be going via the hull. Personally I think that I would went my GI to switch at around 1-volt

 

As to the model it can be seen in many chandlers with no name

 

Keith

[Keith M]

Interesting, a few questions if you don't mind....

 

Did the boat have a steel hull or not, was it tested for a proper hull earth bond, did it have a working RCD and exactly what GI and equipment was used???

 

If conduction IS a problem, one way round it is connect a suitable capacitor across the GI which will conduct AC but block DC. Normally a steel boat sitting in the water will act sufficiently as a capacitor to prevent conduction problems.

 

cheers, Pete.

~smpt~

Hello Pete

 

Sorry I have not been able to master multi quoting

 

Yes it did have a steel hull

 

There was a good Hull earth bond and clearly marked most are not

 

No RCD Fitted which is typical because a GI was installed the answer supplied by the builder to the owner

 

There was no manufactures marking on the unit

 

Washing machine, Oven and high output combi

 

Keith

[nicknorman]

Well I for one wouldn't accept that a GI is an electrical switch. A switch is a device whose conductivity can be turned on and off by the user.

 

Secondly, there can be no one-conductor current flow unless capacitor is involved. So if the GI is not in conduction, it doesn't mean that switch mode PSU transients must be going to earth via the hull, it probably means that the capacitance of the boat is sufficient to absorb them. And even if they are exiting the boat via effectively a single conductor, it is AC and therefore not going to cause galvanic corrosion.

 

The issue can be that the combined voltage of an electrolytic DC potential between hull and electrical shore earth, and the half cycle of the AC transients in the appropriate polarity, can overcome the GI threshold and allow DC current to flow through the GI thus causing corrosion. This won't happen if the GI threshold is greater than this combination of voltages. If there is no DC potential between hull and water, the transients from the SMPSU may or may not leak into the water in tiny quantities, but since they are AC It doesn't matter.

[Keith M]

An interesting account regarding Electric Shock Drowning can be read on the ABYC site. This phenomena has only become apparent after a young American boy died in 1999, whilst returning to his father's boat after swimming in a fresh water river. Initially, it was believed that he had drowned, but his mother recalled that the boy's head was never submerged whilst he was in the water.

 

In fact he had been electrocuted because a nearby boat had faulty wiring and was leaking an electrical current into the water! Since the incident the boy's father has worked tirelessly to create awareness of this silent danger to an unsuspecting American public. I wonder whether we British are also aware of this potentially fatal phenomenon?

 

Hello Doorman

 

Yes a small number of people within the UK are fully aware of the very terrible accident which took place back in the late 90's in the USA

 

Unfortunately most people within the UK believe that it would never happen in this country

 

But with so little or no testing being conducted on new boats and people undertaken DIY installation who have no idea it will happen here soon.

 

Keith

[nicknorman]

 

Hello Doorman

 

Yes a small number of people within the UK are fully aware of the very terrible accident which took place back in the late 90's in the USA

 

Unfortunately most people within the UK believe that it would never happen in this country

 

But with so little or no testing being conducted on new boats and people undertaken DIY installation who have no idea it will happen here soon.

 

Keith

 

Yes it may happen at some point in the future in the UK, however not before thousands have died on the roads, from lung cancer, from liver failure, from drowning (without the aid of electrocution), and quite a few through falls around canals etc. A measure to reduce the risk of death should be proportionate not only to the severity of the event (death is obviously pretty severe) but also to the probability of it happening. Since it has never yet happened in the UK I consider the probability to be very low, though not of course zero. Therefore a perfectly safe system is not called for, only a reasonably safe one.

 

It is of course pretty rare to find people swimming in our canals near boats attached to shore power, something which may help our statistics over the USA's

Edited August 19, 2013 by nicknorman

[smileypete]

 

Chris W's GI has a capacitor built in. I think it's a Sterling model...

 

If I wanted to add a capacitor to my 70 amp GI, could you suggest a suitable one?

 

I'm veeery leery of recommending something that very likely shouldn't be needed.

 

Any small amount of AC leakage from on board equipment, should be conducted through the hull earth bond and out through underwater hull/metalwork without biasing the GI into conduction.

 

Now IF there is excessive 50Hz AC voltage across the GI or the status monitor lights up it could be due to one or more of:

 

Hull earth bond missing or defective

Neutral earth short

Excessive leakage from live to earth from defective equipment on boat

RCD defective and not tripping at the rated trip current

RCD bypassed or missing from installation

Shoreline earth fault

Fault on nearby shore based equipment

Nearby boat with serious AC or DC leak to water

 

I would MUCH rather investigate for all these possible problems than hide the problem with a huuuuge capacitor, and so to me an LED status monitor is much more useful than such a capacitor.

 

If the boat is fibreglass or wood it's more likely the GI will conduct with a small amount of AC leakage, and a capacitor could help in that situation, but I'd much rather rule out the above first.

 

Something else that would help is to get a GI with a higher turn on voltage, which the ones with the LED status monitors have, otherwise the LEDs won't light.

 

If you like why not get in touch with Safeshore and ask them about it. But if some GI manufacturers fit capacitors and it sells more GIs for them, fine

 

As for the high frequency switching noise from SMPS, I do think that the duty cycle of the switching spikes is extremely low, such that say 10 years of SMPS use would be equivalent to a few days of shoreline use without a GI.

 

If people want to be 100.000000% 'certain' and spend out and put an IT aboard a steel hulled canal boat, all power to them, but I don't think it's really warranted and the safety risks to the user aren't worth it.

 

Having an IT on a 250K yacht that's sailing round the world and plugging into all manner of different marina supplies may be a different story, granted.

 

cheers, Pete.

~smpt~

Edited August 19, 2013 by smileypete

[Keith M]

Interesting reading on the smartgauge site regrading GI's and IT's

 

Keith

[Doorman]

Yes it may happen at some point in the future in the UK, however not before thousands have died on the roads, from lung cancer, from liver failure, from drowning (without the aid of electrocution).

 

It is of course pretty rare to find people swimming in our canals near boats attached to shore power, something which may help our statistics over the USA's

It was our Paddy that I was mainly concerned about. He used to swim in one of our previous marinas but thankfully not any more!

[Keith M]

 

Yes it may happen at some point in the future in the UK, however not before thousands have died on the roads, from lung cancer, from liver failure, from drowning (without the aid of electrocution), and quite a few through falls around canals etc. A measure to reduce the risk of death should be proportionate not only to the severity of the event (death is obviously pretty severe) but also to the probability of it happening. Since it has never yet happened in the UK I consider the probability to be very low, though not of course zero. Therefore a perfectly safe system is not called for, only a reasonably safe one.

 

It is of course pretty rare to find people swimming in our canals near boats attached to shore power, something which may help our statistics over the USA's

 

Let's hope no one falls in

 

Keith

[nicknorman]

 

Let's hope no one falls in

 

Keith

As I said, it could happen but its an unlikely combination (falling in near a boat with a live hull). As evidenced by the fact that its never happened in UK inland waters. Its far more likely that someone will get crushed between a boat and a lock landing, fall from a bottom gate, get minced by a prop etc. I am not one to think that therefore boating should be banned, in the same way that I don't think GIs should be banned because its possible they could cause a problem. If one is that risk averse, its better to stay in bed (although of course more people die in bed etc etc)

[smileypete]

Big problem with boat based ITs is that the shoreline if not RCD protected can short to a steel hull and make it live.

 

With GIs this would not be a problem as the hull would be held at earth potential by the GI.

 

BTW the electocution swimming fatalities in the US are almost always caused because they don't routinely fit RCDs on marina shorelines.

 

http://www.google.co.uk/search?&q=gfcis+swimmers+marinas

 

cheers, Pete.

~smpt~

[by'eck]

Interesting account of the pro's and con's of using a capacitor to conduct AC across a GI here.

 

I note the comment ABYC continue to list it as optional in their specifications, although apparently now mandatory for them.

 

Quoting from the Sterling GI manual on further ABYC changes to mandatory spec:

 

The maximum current on a 30 amp system has been changed from a peak of 5000 amps until a fuse blows (about half a cycle) to a new standard of 5000 amps for one complete cycle. No current standard diodes could meet this specification economically so a new block diode was developed.

 

The reason for this is to ensure that if a live wire falls onto a metal surface, the GI has a high enough specification to remain on line until some of the fuses on the boat or the pontoon fail in order to break the voltage.

[Doorman]

Big problem with boat based ITs is that the shoreline if not RCD protected can short to a steel hull and make it live.

 

With GIs this would not be a problem as the hull would be held at earth potential by the GI.

 

BTW the electocution swimming fatalities in the US are almost always caused because they don't routinely fit RCDs on marina shorelines.

 

http://www.google.co.uk/search?&q=gfcis+swimmers+marinas

 

cheers, Pete.

~smpt~

Hi Pete,

 

The moral of the story is "Don't moor your boat in the States!"

 

As a former employee of an American company whose record on safety procedures was very good, I find it quite surprising that their marinas are so negligent when it comes to electrical equipment.

 

Mike

[Keith M]

Big problem with boat based ITs is that the shoreline if not RCD protected can short to a steel hull and make it live.

 

With GIs this would not be a problem as the hull would be held at earth potential by the GI.

 

BTW the electocution swimming fatalities in the US are almost always caused because they don't routinely fit RCDs on marina shorelines.

 

http://www.google.co.uk/search?&q=gfcis+swimmers+marinas

 

cheers, Pete.

~smpt~

 

Hello Pete

with any boat based IT system

I would always have an RCD either side of the IT

And would not rely on the power bollard RCD to be working

Also how often do people test there shore power cable for continuity

 

Keith

[nicknorman]

Hello Pete

with any boat based IT system

I would always have an RCD either side of the IT

And would not rely on the power bollard RCD to be working

Also how often do people test there shore power cable for continuity

 

Keith

I think its a valid point about shore power bollard RCDs not being routinely tested. However this issue is not overcome by the IT over GI debate since it seems to me that one of the weakest points in the system is your own shore power cable, subject to flexing, wear and tear, maybe dangling in the water, maybe operated by someone who doesn't remember to connect the shore end last and disconnect it first etc. For those who are risk averse surely checking the bollard RCD is the best solution?

[by'eck]

 

Hello Pete

with any boat based IT system

I would always have an RCD either side of the IT

And would not rely on the power bollard RCD to be working

Also how often do people test there shore power cable for continuity

 

Keith

 

How would an onboard RCD on the input side of an IT compensate for lack of RCD on power bollard?

 

BTW on the subject of cable check, a simple mains integrity check light such as one below gives indication of earth or neutral not connected as well as reverse polarity. Its available stand-alone and mine fits neatly into the consumer unit to display before I operate the main onboard RCBO, giving a useful indication of shore power lead being live as well as correctly fed.

 

Edited August 20, 2013 by by'eck

[bizzard]

What on earth is an ''IT'' please, is IT some kind of irritating itchy insect like a flea ?

[nicknorman]

 

What on earth is an ''IT'' please, is IT some kind of irritating itchy insect like a flea ?

Yes.

 

Or no, its what we in Scotland have as our early evening meal (well for those unlike me who aren't really English anyway!) (IT = high tea, gerrit?).

 

Im sure you know really bizzyboy, but on the offchance you don't, its isolation transformer.

[bizzard]

 

 

Yes.

 

Or no, its what we in Scotland have as our early evening meal (well for those unlike me who aren't really English anyway!) (IT = high tea, gerrit?).

 

Im sure you know really bizzyboy, but on the offchance you don't, its isolation transformer.

Thank you Nick, gorrit.

[Keith M]

 

How would an onboard RCD on the input side of an IT compensate for lack of RCD on power bollard?

 

​It's a requirement of the current BMEA code of practice

 

BTW on the subject of cable check, a simple mains integrity check light such as this one gives indication of earth or neutral not connected as well as reverse polarity. Mine is fitted neatly into the consumer unit to display before I operate the main onboard RCBO and gives a useful indication of shore power lead being live as well as correct.

 

Unfortunately most owners or boat builders do not go the lengths that you have gone to.

 

Keith

[by'eck]

 

 

How would an onboard RCD on the input side of an IT compensate for lack of RCD on power bollard?

 

​

 

It's a requirement of the current BMEA code of practice

 

Keith

 

 

Yes I have one on my main AC shore power input, but with my eyes open to the fact it wouldn't compensate for lack of one on shore based pedestal.

 

Your post:

 

I would always have an RCD either side of the IT

And would not rely on the power bollard RCD to be working

 

is a little ambiguous. Apologies if I originally misunderstood.

[Doorman]

Hi Richard,

 

Thanks for the link to the mains integrity check light, a must for all boaters who wish to stay safe!

 

Mike

[GUMPY]

Being really picky the IT should be at the supply not on the boat.....

[Doorman]

Being really picky the IT should be at the supply not on the boat.....

Yeah Julian,

 

But we would need a hell of a long shore line lead whenever we went cruising on that basis!

[by'eck]

Hi Richard,

 

Thanks for the link to the mains integrity check light, a must for all boaters who wish to stay safe!

 

Mike

 

You can buy the basic indicator from Philippi without panel, part # 514310230 priced €14.20 + 19% VAT a couple of years ago. Although based in Germany their delivery service is within a couple of days.

 

It requires to be wired to incoming live, neutral and earth, ideally immediately after shore power feed.

 

Although I haven't tried it otherwise, it occurs to me that its earth connection must be before the GI (if fitted) since I doubt the tiny current it draws would cause the GI to conduct, in which case it would show an earth fault if fitted after.

 

Indicator fitted into consumer unit.

 

Edited August 20, 2013 by by'eck