Galvanic isolator

[gary955]

I've frequently been on shore power for the last three years without a GI and when I had my boat blacked recently it showed no ill effects. However I'm now on a new mooring and am thinking that perhaps I've pushed my luck far enough and it's time to get protected.

I guess I should put the GI in the earth line downstream of the socket (on the boat) that the shore lead plugs into, but this is the same socket that I plug the inverter into when away from shore power.

Will it matter that the inverter will run through a GI when in this configuration?

[canals are us?]

When I installed mine I took the earth wire coming into the boat from the external hookup plug and connected it to one side of the GI using a ring clamp. Then connected the other end of the GI using another ring glamp and connected it to the earth bar inside the mains 240 volt consumer unit.

Ie disconnect incoming earth wire to earth point inside 240 volt distribution unit and connect the wire to one side of your GI. then attatch a wire to the other end of the GI and connect back to the consumer unit earth where you had previously disconnected it. Job done.

 

James

[nicknorman]

I've frequently been on shore power for the last three years without a GI and when I had my boat blacked recently it showed no ill effects. However I'm now on a new mooring and am thinking that perhaps I've pushed my luck far enough and it's time to get protected.

I guess I should put the GI in the earth line downstream of the socket (on the boat) that the shore lead plugs into, but this is the same socket that I plug the inverter into when away from shore power.

Will it matter that the inverter will run through a GI when in this configuration?

No it won't matter. Just remember to check the GI is serviceable (not short or open circuit) from time to time, or any time the breaker trips.

[Keith M]

The best protection is an Isolation transformer

 

If a GI fails you will not know

 

Keith

[bigcol]

I have a remote warning panel, which lights up if gos faulty open circuit.

Paid a little more for it, from a main company that sells these.

Nice chap

 

 

Col

[blackrose]

The best protection is an Isolation transformer

 

If a GI fails you will not know

 

Keith

And how will you know if an IT fails?

I have a remote warning panel, which lights up if gos faulty open circuit.

Paid a little more for it, from a main company that sells these.

Nice chap

 

 

Col

Me too. Mine is a safeshore marine GI. If you're getting a GI get a good one.

[Keith M]

And how will you know if an IT fails

 

That's simply

No incoming AC

 

Keith

Edited June 12, 2015 by Keith M

[blackrose]

 

That's simply

No incoming AC

 

Keith

I'm sure I've read that it is possible in certain circumstances to have an AC supply through an IT that isn't working properly. Perhaps that was a specific IT that wasn't very good.

 

Anyway, if you have a GI you're supposed to test it regularly and if you do that you'll know if it's not working.

Edited June 12, 2015 by blackrose

[nicknorman]

That's simply

No incoming AC

 

Keith

I suppose that's another way of saying that fitting an IT = introducing a new failure point that will put the lights out if it goes wrong!

Whereas if a GI goes wrong, nothing adverse happens. Of course we know that a failed GI (open circuit) will result in no protection from that very rare event of a mains fault eg hull becoming live, but what is the hazard for someone on board? The only hazard with a live hull is to someone not onboard, or only partially onboard. But so it is with an installed IT - for probably the most likely fault, a chafed shore power cable making the hull live, an IT gives no protection. So unless the IT is on the bank, I suggest it is something of a myth to maintain that an IT is intrinsically safer than a GI.

[Neil Smith]

I bought a sterling GI that has 2 warning lights one if more than 2 volts is going through it and one for a major fault or its stopped working eg no protection, I was thinking I could wire in a buzzer to the latter to give instant warning.

 

Neil

[gary955]

Thank you nicknorman for answering my original post

[Keith M]

Of course we know that a failed GI (open circuit) will result in no protection from that very rare event of a mains fault eg hull becoming live, but what is the hazard for someone on board? The only hazard with a live hull is to someone not onboard, or only partially onboard. But so it is with an installed IT - for probably the most likely fault, a chafed shore power cable making the hull live, an IT gives no protection. So unless the IT is on the bank, I suggest it is something of a myth to maintain that an IT is intrinsically safer than a GI.

I suppose that's another way of saying that fitting an IT = introducing a new failure point that will put the lights out if it goes wrong!

Whereas if a GI goes wrong, nothing adverse happens.

If a fault does devolve and the GI has failed some body touching the out side of your boat may receive a fatal shock, is that not want the BSS is about third party liability.

 

Firstly what is a GI in its basic form its an electronic switch in the earth cable of the 230-volt supply.

 

And lets assume that you fit such a devices to your washing machine at home it would just be allow because it is unsafe so why fit such a device to your NB.

 

Keith

[nicknorman]

If a fault does devolve and the GI has failed some body touching the out side of your boat may receive a fatal shock, is that not want the BSS is about third party liability.

 

Firstly what is a GI in its basic form its an electronic switch in the earth cable of the 230-volt supply.

 

And lets assume that you fit such a devices to your washing machine at home it would just be allow because it is unsafe so why fit such a device to your NB.

 

Keith

If a fault develops and the GI has failed, somebody touching the outside of you boat will trip the shore bollard RCD and so NOT receive a fatal shock. In just the same way as would happen on a boat with an IT and a chafed shore power lead.

 

Many houses, ours included, do not have RCDs in the socket supply so you are not comparing like with like.

 

You mention the BSS and as you say, the BSS is about third party liability (in part) so how come the BSS allows GIs?

 

Being realistic about it, if your hull becomes live, chances are the shore bollard RCD will trip anyway, due to the conductivity of the impure canal water and/or physical contact between the boat and the shore. This applies both to a failed GI plus boat internal fault, or a chafed shore power lead.

 

The only scenario where it seems likely that a fatality would occur is with a chafed shore lead or GI fault + internal boat fault AND water that is very low resistance AND someone deciding to swim near your boat such that they get into an area of strong voltage gradient which disables them sufficiently to make them drown. One doesn't see folk swimming in marinas very often!

 

But my primary point is that if GIs are so dangerous, how come we NEVER EVER hear of folk dying as a result of them, meanwhile folk die from driving through tunnels, sinking in locks, falling of the boat and getting minced up or crushed, falling into locks, and most commonly of all, dying from other natural causes. Death from failed GI just doesn't feature at all in ways to shuffle off the mortal coil.

Edited June 14, 2015 by nicknorman

[GUMPY]

There have been quite a few deaths in the USA from electrocution in water due to faulty electrics on boats.

However due to the way deaths are recorded in the UK it would only be listed as drowning so we would never know if it was due to electrocution.

Reading your post it imples to me that if a boat has a failed GI then it is still safe due to the RCBO on shore, there is no guarantee that an RCBO would trip if the boat is in fresh water so no limit to the current passing due to the fault.

[nicknorman]

There have been quite a few deaths in the USA from electrocution in water due to faulty electrics on boats.

However due to the way deaths are recorded in the UK it would only be listed as drowning so we would never know if it was due to electrocution.

Reading your post it imples to me that if a boat has a failed GI then it is still safe due to the RCBO on shore, there is no guarantee that an RCBO would trip if the boat is in fresh water so no limit to the current passing due to the fault.

The "deaths in the USA" line is oft quoted but never backed up with specific cases or circumstances which would allow us to consider whether it could, or would be likely to, happen on a UK canal or marina. So for the time being I'm putting it in the 'urban myth" category.

 

I'm not saying a boat with a tripped GI is totally safe, what I am saying is that for perhaps the most likely fault, a chafed shore power cable, neither the GI nor the IT (installed on the boat) give any protection. Of course it is possible to have a fault develop within the boat that puts the hull live, and then the scenarios I mentioned above apply, just as they do with a chafed shore cable.

 

You say "...fresh water so no limit to the current passing due to a fault" but any current exiting the boat via the water or a person will present as a differential current to the bollard RCD or RCBO and if it exceeds 30mA then it will trip. That is hardly "no limit to the current" and exactly the same as when an IT or operative GI is fitted.

[GUMPY]

That was badly worded on my part;

so are you saying its safe provided there is a shore side RCBO even if the hull has no earth bond?

As for deaths feast your eyes on this list

http://www.qualitymarineservices.net/electric_shock_drowning_incident_list.html

Hardly an urban myth

ETA

 

Allthough not all related to boats this makes interesting reading

http://www.nfpa.org/~/media/15668590293D419C85CF9144036C59F4.pdf

 

I use an IT with RCBO in the shed to feed the boat just to be safe, well as safe as electricity can ever be.

Edited June 14, 2015 by Loddon

[smileypete]

That was badly worded on my part;

so are you saying its safe provided there is a shore side RCBO even if the hull has no earth bond?

As for deaths feast your eyes on this list

http://www.qualitymarineservices.net/electric_shock_drowning_incident_list.html

Hardly an urban myth

ETA

 

But you're omitting to state that shoreside RCDs are very seldom fitted over in the US, maybe you can fully explain why...

 

I use an IT with RCBO in the shed to feed the boat just to be safe, well as safe as electricity can ever be.

 

Yeah but most boaters here won't be able to keep their IT on the bank, only on the boat, which negates any safety advantage.

 

If anyone wants to actually improve the safety of their boating, all they need to is look at the statistics from the BSS of accidents that actually happen, not some expert argument about infinitesimal risks...

 

I've frequently been on shore power for the last three years without a GI and when I had my boat blacked recently it showed no ill effects. However I'm now on a new mooring and am thinking that perhaps I've pushed my luck far enough and it's time to get protected.

I guess I should put the GI in the earth line downstream of the socket (on the boat) that the shore lead plugs into, but this is the same socket that I plug the inverter into when away from shore power.

Will it matter that the inverter will run through a GI when in this configuration?

 

As said the inverter will run fine

 

But, I'd use a plug in socket tester (with the three lights) to help check the inverter has a functioning earth, otherwise the RCD won't give protection - even though the test button works.

 

As for the GI just fit a decent one like the ones from Safeshore with the status LED monitor. Follow their instructions for install and use, and enjoy your boating...

 

(And of couse if you're in the USA don't swim in a marina - consult their accident statistics first )

 

cheers, Pete.

~smpt~

Edited June 14, 2015 by smileypete

[nicknorman]

I've got to rush but Pete has made the primary point which is that in the U.S. they barely bother with earths at all, never mind RCDs. So you are not comparing like with like even before you put a x10 factor on the population size. Obviously having a IT on the bank means that you won't die from electric shock - instead you will die from tripping over it in the dark, falling in the cut having banged your head, and drowned.

[cuthound]

In my working days, one of the tasks my group had was to investigate all high impact power failures and near misses.

 

Wound devices (transformers and motors) failed about 3 times more often than power aemi-conductets, when weighted for population.

 

This was with very high quality components, which may not be the case with marine IT's and GI's.

 

My boat is fitted with a Vetus GI, which although reliable, has no failure (or even working) LED's and is mounted in such a place as to be extremely difficult to test. Ideally it needs a "door" cutting into the panel which covers it, to make access easier.

 

Does anyone know of a good carpenter in the Tamworth area that could do this work?

[Neil Smith]

don't they use 120 volts in usa so people don't get electrocuted.

 

Neil

[GUMPY]

I've got to rush but Pete has made the primary point which is that in the U.S. they barely bother with earths at all, never mind RCDs. So you are not comparing like with like even before you put a x10 factor on the population size. Obviously having a IT on the bank means that you won't die from electric shock - instead you will die from tripping over it in the dark, falling in the cut having banged your head, and drowned.

It is in the far corner of the shed so doubt I would trip over it even if I hadn't turned the light on. If the light was off one would be far more likely to trip over the elsan emptying point with way more disasterous consequences.

It seems that there are devotees of both GI and IT who wont have a word said against their choice just like pump out v cassette.

One thing to bear in mind in the future if BS7671 is extended to cover boats the way it now does caravans there will be no "switches" allowed in the PE conductor

[nicknorman]

It seems that there are devotees of both GI and IT who wont have a word said against their choice just like pump out v cassette.

One thing to bear in mind in the future if BS7671 is extended to cover boats the way it now does caravans there will be no "switches" allowed in the PE conductor

I think either an IT or a GI is fine, they each have their pros and cons. I just object to proponents of the IT route, dissing GIs without any scientific justification.

 

I'm not sure what the exact wording is in BS7671 but if it just precludes "switches" in the PE then it will be easy to say that a diode is not a switch.

Edited June 14, 2015 by nicknorman

[Keith M]

I think either an IT or a GI is fine, they each have their pros and cons. I just object to proponents of the IT route, dissing GIs without any scientific justification.

 

I'm not sure what the exact wording is in BS7671 but if it just precludes "switches" in the PE then it will be easy to say that a diode is not a switch.

 

Hello Nick,

 

Over an average year I will inspect 20+ boats around the UK waterways

Of those 20+ boats around 50% will have failed GI's I have yet to find one which has a failed IT

I look at two boats last week both had GI's one of which had failed

I feel the above facts is a good reason using your words to diss a GI

 

If the BS 7671 does get extended to inland marine

Any interruption of any earth wire by any means will not be expectable

Which now applies to all vehicles that can produce an AC voltage either by a generator or an inverter

 

Keith

[nicknorman]

Hello Nick,

 

Over an average year I will inspect 20+ boats around the UK waterways

Of those 20+ boats around 50% will have failed GI's I have yet to find one which has a failed IT

I look at two boats last week both had GI's one of which had failed

I feel the above facts is a good reason using your words to diss a GI

 

If the BS 7671 does get extended to inland marine

Any interruption of any earth wire by any means will not be expectable

Which now applies to all vehicles that can produce an AC voltage either by a generator or an inverter

 

Keith

 

Yes GIs can fail, but it seems unlikely they would fail unless there had been an "event" such as a short between live and earth, hence my advice to check the GI any time a breaker trips. It has to be said though, that the risk to humans of having a failed GI is not great - I come back to asking how many of those boats you found with failed GIs had caused fatal shocks? I'll agree it is greater than the risk presented by an IT installed on the boat (chafed shore cable) but both the risks are very small and being realistic about it, I'm not that fussed about choosing between one risk that is tiny, and another risk that is even tinier.

 

ITs are slightly inelegant in that they hum and dissipate power whereas the GI is elegant in that it doesn't need to pass any power under normal circumstances, and doesn't get warm / waste power. It does of course have the weakness of potentially failing open circuit following a major fault with the mains installation on the boat or an appliance.

 

Oh that reminds me of a question - of all those GIs that you found faulty, had they failed open or short circuit?

 

Finally regarding the wiring regs, I'd have to see the exact wording because a diode doesn't interrupt the PE. what it might do is be unable to carry the max fault current without failing, but that is an issue of its rating, a bit like installing an inadequate sized PE conductor.

Edited June 14, 2015 by nicknorman

[ditchcrawler]

120 volts will kill you in the right circumstances as would 50 volts