Isolating Transformer

[Theo]

Having been thinking that at some time in the future I might well want a shore line and having read and been convinced by Gibbo's web site regarding the use of Galvanic isolators, I thought that I would look up a transormer to find out how much it would cost.

 

I fear that I have drawn a blank with supplier and cost. Could someone provide me with a link, please?

 

Nick

Edited September 13, 2008 by Theo

[Guest TerryL]

Having been thinking that at some time in the future I might well want a shore line and having read and been convinced by Gibbo's web site regarding the use of Galvanic isolators, I thought that I would look up a transormer to find out how much it would cost.

 

I fear that I have drawn a blank with supplier and cost. Could someone provide me with a link, please?

 

Nick

 

Try this one, at £180 it is double insulated so avoids the earthing to hull problem with power supplies and onboard isolation transformers. It can be used on shore (the correct way for all other IT's) or free standing onboard with no shore earth connection to the hull required provided the shore cable is wired directly into the transformer without any onboard plug connection/switchgear etc. involved.

 

http://www.airlinktransformers.com/transfo...transformer.asp

Edited September 13, 2008 by TerryL

[Dr Bradley]

http://www.victronenergy.com/isolation-transformers/

 

Victron do them, many suppliers - try

 

http://www.canalboatbits.co.uk/index.html

[Guest TerryL]

http://www.victronenergy.com/isolation-transformers/

 

Victron do them, many suppliers - try

 

http://www.canalboatbits.co.uk/index.html

 

It is common knowledge that a shore supply should be earthed to the hull, IET regulations also state that the earth wire should be permanently connected and should not be switched or interrupted by any device (the argument against galvanic isolators). Fitting a metal cased isolation transformer installation onboard does not alter those requirements and makes it useless unless fitted onshore.

 

The common practice when fitting an IT of leaving the shore earth unconnected to the hull to provide the shore isolation does not follow safety regulations, is unacceptable and again makes the IT useless for shore isolating purposes. You don't need the IT if the earth is disconnected! A supply live fault to the hull if unearthed will leave the vessel live in the water or onshore! If you bring a shore supply onto a vessel then it must be earthed to the hull permanently, end of argument.

 

The Victron IT does not follow safety earth regulations in that the user is required to remove and alter earth links when afloat and alter them when the vessel is ashore. Most people would not remember to do that and may not be proficient enough with wiring and it can be dangerous. The links leave the vessel unearthed afloat and potentionally unearthed ashore. If the link is left in, it makes the vessel safe but the IT is completely useless.

 

The Airlink double insulated IT as previously mentioned can overcome these problems if installed correctly and provide safer galvanic isolation.

[Dr Bradley]

Thanks for that info, saves me wasting money as I was considering one. But it begs the question - why do they make them?

[bottle]

Colin.

 

Some more reading for you:

 

http://www.smartgauge.co.uk/galv2.html

 

Which leads on to this page.

 

http://www.smartgauge.co.uk/galv_tran.html

[smileypete]

Having been thinking that at some time in the future I might well want a shore line and having read and been convinced by Gibbo's web site regarding the use of Galvanic isolators, I thought that I would look up a transormer to find out how much it would cost.

 

I fear that I have drawn a blank with supplier and cost. Could someone provide me with a link, please?

 

I wouldn't recommend an onboard isolation transformer, as there is no protection from shoreline to hull faults.

 

Gibbo's site should cover this important safety aspect, but doesn't

 

I would therefore recommend a galvanic isolator.

 

cheers,

Pete.

Edited September 14, 2008 by smileypete

[Dr Bradley]

To my limited knowledge, Gibo's site appears to contradict TerryL's comments. It also seems a Galvanic Isolater won't do the job if modern electrical equipment is fittedon the boat. Another case of the more I learn, the less I know. I should never have got involved in an electricity thread!

[Guest TerryL]

Thanks for that info, saves me wasting money as I was considering one. But it begs the question - why do they make them?

 

Personally I think galvanic problems due to a shore supply earth are overrated on fresh water but this makes earthing even more important due to the lower conductivity than salt water. However, salt water does appear to be more likely to set up erosive galvanic currents between the shore and hull. The only safe way to eliminate the earth connection that completes the galvanic circuit is to use an isolation transformer on the shore or at least inline between the shore and vessel with a fully insulated and waterproof transformer and supply sited on deck or nearby.

 

An isolation transformer is just another product to sell with a demand from customers to fit it onboard. Without any real safety regulation the manufacturers are free to devise misleading diagrams showing the IT in mid air and confusing link connections to earth without addressing the real practical issues of safely earthing the supply or the IT onboard which they cannot overcome. This means they simply do not earth the vessel or IT which can and does cause dangerous situations and over reliance on the shore RCD which can have a high failure rate especially in a marine environment. There are things you simply cannot compromise on with electricity and earthing is a fundimental requirement.

 

Where as Gibbo is looking at this from an electronics viewpoint, as an old electrician I can see the inherent safety problems and the alarming conflict with regulations with the installation of GI's and IT's. It is no exaggeration to state that all vessels with a GI or onboard IT do not meet the required electrical safety requirements and regulations concerning the supply earthing and are all potentionally dangerous. An appalling state of affairs!

[Dr Bradley]

The only answer would seem to be avoding shore power. I think I'll be fitting neither as I don't expect to be on shore power often.

[Guest TerryL]

I wouldn't recommend an onboard isolation transformer, as there is no protection from shoreline to hull faults.

 

Gibbo's site should cover this important safety aspect, but doesn't

 

I would therefore recommend a galvanic isolator.

 

cheers,

Pete.

 

The problem with galvanic isolators from a purely safety aspect, more so in fresh water is that the IET regulations state that an earth wire should be continuous with no switching device in it. A GI, being a semi conductor, is a switching device that can easily fail.

 

However, contrary to that there is now a recent standard for GI's but unfortunately there appears to be no GI manufactured that I've seen yet that can meet that standard that can reasonably expect to repeatedly withstand the very high fault currents of many thousands of amps for milliseconds that are experienced in a short circuit conditions before a fuse will blow!

 

The GI's currently available are cheap weedy unapproved affairs (dispite claims to the contrary) that fail very easily leaving no earth connection and rely almost entirely on the shore RCD which are also not totally reliable. The only thing you can rely on is the correct fuse with a good earth.

[Guest TerryL]

The only answer would seem to be avoding shore power. I think I'll be fitting neither as I don't expect to be on shore power often.

 

I think you're right, you only need to isolate if you're sure you do have a problem when on a permanent supply which is less likely on fresh water. The safe options for shore isolation are preferably an inline IT or a substantial GI to the approved standard, although all GI's have a much less effective isolation ability and may not even isolate at all.

[Theo]

It is common knowledge that a shore supply should be earthed to the hull, IET regulations also state that the earth wire should be permanently connected and should not be switched or interrupted by any device (the argument against galvanic isolators). Fitting a metal cased isolation transformer installation onboard does not alter those requirements and makes it useless unless fitted onshore.

 

The common practice when fitting an IT of leaving the shore earth unconnected to the hull to provide the shore isolation does not follow safety regulations, is unacceptable and again makes the IT useless for shore isolating purposes. You don't need the IT if the earth is disconnected! A supply live fault to the hull if unearthed will leave the vessel live in the water or onshore! If you bring a shore supply onto a vessel then it must be earthed to the hull permanently, end of argument.

 

The Victron IT does not follow safety earth regulations in that the user is required to remove and alter earth links when afloat and alter them when the vessel is ashore. Most people would not remember to do that and may not be proficient enough with wiring and it can be dangerous. The links leave the vessel unearthed afloat and potentionally unearthed ashore. If the link is left in, it makes the vessel safe but the IT is completely useless.

 

The Airlink double insulated IT as previously mentioned can overcome these problems if installed correctly and provide safer galvanic isolation.

 

Oh, yes. I do take your point.

 

This means that the IT needs to sit on the ground next to the shore power supply. This means that it needs to be built rather like of those yellow ones that you hire from Speedyhire. At some point you need to bond the neutral to the hull too which should not be a problem.

 

Nick

[Guest TerryL]

Oh, yes. I do take your point.

 

This means that the IT needs to sit on the ground next to the shore power supply. This means that it needs to be built rather like of those yellow ones that you hire from Speedyhire. At some point you need to bond the neutral to the hull too which should not be a problem.

 

Nick

 

That's exactly right, the Airlink can do that being waterproof and has a ceramic core shield but any weather protected 230v - 230v isolation transformer will do the same job onshore. The input earth is connected to the core and casing as normal and the output neutral should be bonded to the isolated output earth terminal in the transformer or as near as possible as in all stand alone supplies.

[smileypete]

The problem with galvanic isolators from a purely safety aspect, more so in fresh water is that the IET regulations state that an earth wire should be continuous with no switching device in it. A GI, being a semi conductor, is a switching device that can easily fail.

AIUI the IET regulations don't apply to boats.

 

 

However, contrary to that there is now a recent standard for GI's but unfortunately there appears to be no GI manufactured that I've seen yet that can meet that standard that can reasonably expect to repeatedly withstand the very high fault currents of many thousands of amps for milliseconds that are experienced in a short circuit conditions before a fuse will blow!

What length of 2.5mm² shoreline will allow 'many thousands of amps' to flow? Can you post some calculations?

 

I don't think it's an insurmountable problem with the right design.

 

 

The GI's currently available are cheap weedy unapproved affairs (dispite claims to the contrary) that fail very easily leaving no earth connection and rely almost entirely on the shore RCD which are also not totally reliable. The only thing you can rely on is the correct fuse with a good earth.

How many GIs fail in practice? Do you know of any instances?

 

Trouble with fuses relying on a food earth, is that the shoreline can get damaged such that the earth is missing.

 

This is why RCDs are a very worthwhile addition, nothing is totally reliable but they give a huge magnitude of improvement in safety.

 

cheers,

Pete.

Edited September 14, 2008 by smileypete

[Guest TerryL]

AIUI the IET regulations don't apply to boats.

 

 

 

What length of 2.5mm² shoreline will allow 'many thousands of amps' to flow? Can you post some calculations?

 

I don't think it's an insurmountable problem with the right design.

 

 

 

How many GIs fail in practice? Do you know of any instances?

 

Trouble with fuses relying on a food earth, is that the shoreline can get damaged such that the earth is missing.

 

This is why RCDs are a very worthwhile addition, nothing is totally reliable but they give a huge magnitude of improvement in safety.

 

cheers,

Pete.

 

You're right the IET regs don't specifically apply to boats but as from earlier this year marina and boatyard supplies to your boat do. The marina will have obligations as a place of work and under H&S and if they work on your boat. The regs are the accepted standard and for individuals you also have a duty of care, if you injury someone through faulty or substandard electrical work on or to your boat you can be sued for negligence, if you kill anyone you can expect a manslaughter charge.

 

The test standard if I recall correctly is 5000 amps for a certain time repeated 3 times. You wouldn't always get that fault current but a shorter cable is better for it to blow the fuse quicker and keep fault potentials down. The idea is that the GI should be robust enough to withstand the maximum likely fault current without failing, not something to aspire to!

 

I have read and heard of many GI's failing which created a demand for GI's with fault indicators and now sensibly with more substantial diodes.

 

A good earth is essential for any supply, this gives the basic fault protection by dumping the fault current to earth and keeping fault voltages safely below 50 volts until the fuse blows. A poor supply may not have enough fault current to blow the fuse, however, without an earth at all the RCD will not work. The earth continuity can be tested if you think it is faulty and demand it be put right. An RCD is a useful safety device in addition to the basic system but should never be relied on as the only means of protection.

[smileypete]

The test standard if I recall correctly is 5000 amps for a certain time repeated 3 times.

This is not quite the 'many thousands of amps' that you quoted.

 

I asked a simple question, please post some calculations showing what length of shoreline would allow 'many thousands of amps' to flow?

 

 

I have read and heard of many GI's failing which created a demand for GI's with fault indicators and now sensibly with more substantial diodes.

Can you link to anything on the web about 'many GI's failing'? Or post details of where you read about it?

 

 

The reason I posted originally was not to get embroiled in a debate like this, simply to highlight that an on board isolation transformer gives no protection from shoreline to hull faults.

 

If Gibbo's site covered this important safety aspect, I wouldn't need to get involved.

 

A galvanic isolator is not perfect, but it does give protection from shoreline to hull faults.

 

<sigh!>

 

cheers,

Pete.

Edited September 14, 2008 by smileypete

[ditchcrawler]

This is not quite the 'many thousands of amps' that you quoted.

 

I asked a simple question, please post some calculations showing what length of shoreline would allow 'many thousands of amps' to flow?

 

 

 

cheers,

Pete.

 

Is not just the length of you shore line, its all the cables back to the last transformer. To calculate it you work on cable resistance and maximum possible fault currents, something we use to have to work through for specifying switchgear. And no after 10 years of boating as opposed to working I can't remember the formula, I can't even remember the resistivity of copper wire, but just think of the lead on your washing machine and work back to the mains sub station.

[Guest TerryL]

This is not quite the 'many thousands of amps' that you quoted.

 

I asked a simple question, please post some calculations showing what length of shoreline would allow 'many thousands of amps' to flow?

 

 

 

Can you link to anything on the web about 'many GI's failing'? Or post details of where you read about it?

 

 

The reason I posted originally was not to get embroiled in a debate like this, simply to highlight that an on board isolation transformer gives no protection from shoreline to hull faults.

 

If Gibbo's site covered this important safety aspect, I wouldn't need to get involved.

 

A galvanic isolator is not perfect, but it does give protection from shoreline to hull faults.

 

<sigh!>

 

cheers,

Pete.

 

That's a test current not a fault current. The answer is you don't need any shoreline for a fault current of many thousands of amps to flow and I can't be bothered to work out silly and obscure questions and no I can't link to anything on the web, you can do that yourself. If you think I'm wrong you are welcome to prove it with your own facts and figures. It's your choice to use a GI, good luck with it. There's always one!

[Arnot]

Personally I think galvanic problems due to a shore supply earth are overrated on fresh water but this makes earthing even more important due to the lower conductivity than salt water. However, salt water does appear to be more likely to set up erosive galvanic currents between the shore and hull. The only safe way to eliminate the earth connection that completes the galvanic circuit is to use an isolation transformer on the shore or at least inline between the shore and vessel with a fully insulated and waterproof transformer and supply sited on deck or nearby.

 

An isolation transformer is just another product to sell with a demand from customers to fit it onboard. Without any real safety regulation the manufacturers are free to devise misleading diagrams showing the IT in mid air and confusing link connections to earth without addressing the real practical issues of safely earthing the supply or the IT onboard which they cannot overcome. This means they simply do not earth the vessel or IT which can and does cause dangerous situations and over reliance on the shore RCD which can have a high failure rate especially in a marine environment. There are things you simply cannot compromise on with electricity and earthing is a fundimental requirement.

 

Where as Gibbo is looking at this from an electronics viewpoint, as an old electrician I can see the inherent safety problems and the alarming conflict with regulations with the installation of GI's and IT's. It is no exaggeration to state that all vessels with a GI or onboard IT do not meet the required electrical safety requirements and regulations concerning the supply earthing and are all potentionally dangerous. An appalling state of affairs!

Here Here! Well said that man, I agree entirely! I was beginning to wonder when there would be someone prepared to tackle this thorny subject.

 

How long will it be before the sometimes extensive and high power mains systems often installed on boats are subject to any form of testing? Similar systems installed in vehicles that are used as places of work have been tested annually (or at least should have been by law) for many years, I know because thats what I do... Regular testing of the RCD with the button provided gives some assurance but for a reasonable assurance of protection, the whole installation should be tested thoroughly.

 

Regards

 

Arnot

[Big COL]

It is common knowledge that a shore supply should be earthed to the hull, IET regulations also state that the earth wire should be permanently connected and should not be switched or interrupted by any device (the argument against galvanic isolators). Fitting a metal cased isolation transformer installation onboard does not alter those requirements and makes it useless unless fitted onshore.

The common practice when fitting an IT of leaving the shore earth unconnected to the hull to provide the shore isolation does not follow safety regulations, is unacceptable and again makes the IT useless for shore isolating purposes. You don't need the IT if the earth is disconnected! A supply live fault to the hull if unearthed will leave the vessel live in the water or onshore! If you bring a shore supply onto a vessel then it must be earthed to the hull permanently, end of argument.

 

 

What if you use a shore side in line RCD?

 

 

 

 

 

The Victron IT does not follow safety earth regulations in that the user is required to remove and alter earth links when afloat and alter them when the vessel is ashore. Most people would not remember to do that and may not be proficient enough with wiring and it can be dangerous. The links leave the vessel unearthed afloat and potentionally unearthed ashore. If the link is left in, it makes the vessel safe but the IT is completely useless.

 

 

 

Would this apply with a shore side RCD?

 

 

The Airlink double insulated IT as previously mentioned can overcome these problems if installed correctly and provide safer galvanic isolation.

Edited September 14, 2008 by Big COL

[Guest TerryL]

An RCD is a secondary safety device to be use in conjunction with a basic earth protective system and should not be relied on as the sole means of protection, they cannot be guaranteed to work without an earth or at all and can leave the vessel live with a fault, especially in fresh water. Whilst it might still trip if someone comes in contact, it will still give them a nasty shock first and much worse in water. An earth will prevent that unless they touch a live conductor.

 

The tendancy for people to think that an RCD is the answer to everything and earths don't matter is very dangerous. Useful as they are in quickly protecting against direct contact shock, they are no substitute for a system complete with earth that is designed to deal with earth faults and overloads and will still work when an RCD fails.

[Eastern]

An RCD is a secondary safety device to be use in conjunction with a basic earth protective system and should not be relied on as the sole means of protection, they cannot be guaranteed to work without an earth or at all and can leave the vessel live with a fault, especially in fresh water. Whilst it might still trip if someone comes in contact, it will still give them a nasty shock first and much worse in water. An earth will prevent that unless they touch a live conductor.

 

The tendancy for people to think that an RCD is the answer to everything and earths don't matter is very dangerous. Useful as they are in quickly protecting against direct contact shock, they are no substitute for a system complete with earth that is designed to deal with earth faults and overloads and will still work when an RCD fails.

 

That'll be why most domestic electrical equipment is double insulated and does not have an earth connection?

[Denis R]

So who does have the definitive wiring diagram that shows exactly how a 240v system should be configured:

1) with isolation transformer

2) without isolation transformer but with galvanic isolator

3) for a genny hook-up?

[GUMPY]

http://www.smartgauge.co.uk/nb_ac_sys.html