Earth/Hull bonding

[Gibbo]

I walk past his boat everyday. How near are we talking? Surely a giant spark isn't going to arc over and kill me. Wet pontoons perhaps?

 

Oh you'd have to touch it, or touch something it was touching, or fall in the canal, or touch a wet pontoon, or just go anywhere near in fact

 

But only if he had a fault.

 

I suppose technically a spark is posible but it's ridiculously unlikely.

 

Gibbo

 

I walk past his boat everyday. How near are we talking? Surely a giant spark isn't going to arc over and kill me. Wet pontoons perhaps?

 

I would know if my GI was forced into conduction... the LEDs would illuminate. (Sorry couldn't resist)

 

Notice how I very politely didn't comment on the other bit

 

Gibbo

[blackrose]

Notice how I very politely didn't comment on the other bit

 

Gibbo

 

Thanks... It must be a first!

 

On a serious point. Is earth bonding part of BSS electrical installation requirements? If not, why not? And if so why aren't boats without bonded earths failing?

 

Is the same earth bonding issue relevant to inverter produced 240v power?

Edited November 17, 2006 by blackrose

[Osprey Sprinkler]

Just a thought relating to bonding and Isolation Transformers.

 

It has been suggested that the regs require all 230V equipment earths to be bonded to the hull, and that this includes isolation transformers. It is also clear, as gibbo has rightly pointed out, that bonding your isolation transformer chassis to the hull is not clever as it can cause the hull to go live under certain fault conditions.

 

Isn't the obvious conclusion that the IT should not be on the boat in the first place? Shouldn't it be on land, perhaps as part of the shore power bollard, and grounded to true earth?

 

Ashley

[chris w]

The chassis of the IT should be grounded to true earth

[Chris Lingwood]

I've got a physics degree and I'm doing a phd in microwave engineering (ok so not electronics but its not a million miles away) and I think it should be bonded too. You could perhaps have an arguments when you are using an inverter but not with shore power. A live hull = bad! I'd rather it dissolved to be honest!

 

Unless inverter manufactures are a bit dense (or have a very good reason I've not thought of) they should be earthed anyway. They've got a dirty great cable going to the hull via -ve that they could use (and I presume do).

 

I know my boat wasn't earthed when I bought it, but shore power had never been envisaged when it was fitted out so its not as shocking (geddit?!?!? )

[ChrisPy]

I walk past his boat everyday. How near are we talking? Surely a giant spark isn't going to arc over and kill me. Wet pontoons perhaps?

 

if you really want that curry the best thing is to jump onto and off his boat, ensuring that you never make a circuit to earth. just don't drink too much ...........

[Gibbo]

Thanks... It must be a first!

On a serious point. Is earth bonding part of BSS electrical installation requirements?

 

No. But curiously it *is* part of the RCD (recreational craf..........).

 

If not, why not?

 

I'm still trying to get an answer from them. All they ever say is "we are looking into it and are aware of the dangers".

 

 

Is the same earth bonding issue relevant to inverter produced 240v power?

 

No. That's a whole different bag of fish.

 

Gibbo

 

Just a thought relating to bonding and Isolation Transformers.

 

It has been suggested that the regs require all 230V equipment earths to be bonded to the hull, and that this includes isolation transformers. It is also clear, as gibbo has rightly pointed out, that bonding your isolation transformer chassis to the hull is not clever as it can cause the hull to go live under certain fault conditions.

 

 

For ultimate safety the transformer chassis should be bonded to the shoreline earth, then completely isolated from the hull, and inside a case isolated from both, and preferably a non-conductive case.

 

Isn't the obvious conclusion that the IT should not be on the boat in the first place? Shouldn't it be on land, perhaps as part of the shore power bollard, and grounded to true earth?

 

 

Yes that *is* the best solution.

 

Gibbo

 

I've got a physics degree and I'm doing a phd in microwave engineering (ok so not electronics but its not a million miles away) and I think it should be bonded too.

 

Thankyou.

 

We're still waiting to hear about the qualifications of those who think it should *not* be bonded.

 

Not a single one so far.

 

Gibbo

[Sir Nibble]

OK, I am not going to argue with anyone about this, I too would always advocate bonding. But just for information. Supposing I took you up on your offer, there I am swimming around, the potential on your boat begins to rise, assuming for a moment that the water isn't a pretty good earth in its own right, its potential also rises, so does mine. Isn't this similar to the bird on the power line? Why should I be drowning when I am at the same potential as the water around me? unless the water is a good earth and I am being boiled alive. I am at pains to point out that I ask only for information and not arguing your point.

[Gibbo]

OK, I am not going to argue with anyone about this, I too would always advocate bonding. But just for information. Supposing I took you up on your offer, there I am swimming around, the potential on your boat begins to rise, assuming for a moment that the water isn't a pretty good earth in its own right, its potential also rises, so does mine. Isn't this similar to the bird on the power line? Why should I be drowning when I am at the same potential as the water around me? unless the water is a good earth and I am being boiled alive. I am at pains to point out that I ask only for information and not arguing your point.

 

You're assuming that the *entire* canal rises in potential. It doesn't.

 

The earth itself is a pretty damned good conductor. The water nowhere near as good.

 

Assume we managed to get the hull voltage up to 50 volts before tripping the incoming circuit breaker. It's guesswork what we could get the voltage to but let's just assume 50 volts - it doesn't really matter for these purposes what voltage we reach.

 

We now have 50 volts on the hull and zero volts round the edge of the canal and on the bottom of the canal. You are in the middle of this. There will be a voltage gradient along/across your body. As your body is a better conductor than the surrounding water, the bulk of the current will pass through your body not through the water surrounding you. So assume you were pointing directly between the hull and the bottom of the canal out in open water, the top of your body would be at a much higher voltage than your feet.

 

Note that this doesn't apply in salt water. Salt water is such a good conductor that it would be extremely difficult to get a voltage gradient through it. You would need (a wild guess here) tens of thousands of amps to get anything approaching a dangerous level of voltage gradient.

 

So in fresh water this is a much more serious problem than in salt water. The opposite of what intuition would tell many people.

 

Gibbo

Edited November 17, 2006 by Gibbo

[chris w]

Assume we managed to get the hull voltage up to 50 volts before tripping the incoming circuit breaker. It's guesswork what we could get the voltage to but let's just assume 50 volts - it doesn't really matter for these purposes what voltage we reach.

It does!!!!!!

 

If you don't get it up high enough, and the guy's still swimming, it's gonna cost you a lot of beer

[Gibbo]

It does!!!!!!

 

If you don't get it up high enough, and the guy's still swimming, it's gonna cost you a lot of beer

 

LOL. I meant for the purposes of getting a voltage gradient across his body.

 

For the purposes of actually killing him then yes, of course , it matters.

 

Gibbo

[chris w]

For the purposes of actually killing him then yes, of course , it matters.

Doesn't matter to me.............. the guy was a prat for taking you up on your offer in the first place

[miles beyond]

All I can add is that I know many experienced people who have had boats for many years who have a good degree of technical knowledge and who believe that bonding the earth to the hull is just a way of creating more problems and more expense. The evidence produced by Gibbo that this can lead to people drowning is flimsy to say the least.

 

Why not use the earth return on the shoreline? Gibbo asked how one could be certain that there was not a small amount of AC leakage to the hull through a fault on the boat. With a three core double insulated ring main I think one can be reasonably certain that it is not likely. However, given this startling new electronic drowning "evidence" kindly passed on to us by some Deputy Sherriff from Chicken Nuggets, Iowa or wherever we now know that to be absolutely certain there is not a small amount of leakage all we have to do is chuck an obnoxious brat in the cut alongside and wait for the results.

[Gibbo]

All I can add is that I know many experienced people who have had boats for many years who have a good degree of technical knowledge and who believe that bonding the earth to the hull is just a way of creating more problems and more expense.

 

I bet *none* of them are qualified in the field.

 

The evidence produced by Gibbo that this can lead to people drowning is flimsy to say the least.

 

Only if you don't read it. If you actually *read* it, it is pretty compelling. If only by the sheer volume of it.

 

 

Why not use the earth return on the shoreline?

 

 

That makes absolutely no sense whatsoever.

 

Gibbo asked how one could be certain that there was not a small amount of AC leakage to the hull through a fault on the boat. With a three core double insulated ring main

 

 

A 3 core ring main *by definition* isn't double insulated.

 

I think one can be reasonably certain that it is not likely. However, given this startling new electronic drowning "evidence" kindly passed on to us by some Deputy Sherriff from Chicken Nuggets, Iowa or wherever we now know that to be absolutely certain there is not a small amount of leakage all we have to do is chuck an obnoxious brat in the cut alongside and wait for the results.

 

Clearly you didn't read *any* of them.

 

Gibbo

Edited November 17, 2006 by Gibbo

[blackrose]

A 3 core ring main *by definition* isn't double insulated.

 

Can you elaborate?

[Sir Nibble]

OK, so I will be gently cooked due to being part of a series/parallel circuit with the water, which is of such a high resistance that the parallel bit of it will dump all the volt drop on me, but of such a low resistance that the drop between boat and me and me and canal bed is low.

I take no issue with the need for earth bonding but I am extremely dubious about this particular illustration, but then I am just the humble tradesman, only city and guilds, no letters after my name.

 

Gibbo, In my experience there are people with letters after their name, and people with shit under their fingernails, and each is useless at the others job. You seem to have achieved a crossover for which I congratulate you, but I think it unreasonable to assert that a technical argument is settled by comparing qualifications. I have been patronised so many times by graduates who smile at me indulgently whilst asserting the most astonishing rubbish.

[miles beyond]

I bet *none* of them are qualified in the field.

Only if you don't read it. If you actually *read* it, it is pretty compelling. If only by the sheer volume of it.

That makes absolutely no sense whatsoever.

A 3 core ring main *by definition* isn't double insulated.

Clearly you didn't read *any* of them.

 

Gibbo

 

Yes they are.

 

You originally wrote in the galvanic isolator soap opera to the effect that "if the earth was not bonded to the hull but simply returned through the shoreline (why that makes no sense to you is a mystery to me) then the galvanic corrosion risk was the same as not being hooked to a landline at all"

 

Therefore you agree that not bonding the earth to the hull greatly reduces the galvanic corrosion risk. You just have this bee in your inverter about drowning through electrical leakage. There is no example of this on the UK waterways. And if so, why are other mammals not beinbg decimated? - I have been on boats for a long time and have not noticed an undue amount of dogs, rats, voles or other mammalia drifting past.

 

I don't know what your interest is in trying to get this made a part of the BSS but I for one will not be thanking you if you succeed.

[Gibbo]

Can you elaborate?

 

Look up "double insulated" or "class II" equipment.

 

By definition it has 2 conductors not 3.

 

Gibbo

[blackrose]

Yes they are.

 

You originally wrote in the galvanic isolator soap opera to the effect that "if the earth was not bonded to the hull but simply returned through the shoreline (why that makes no sense to you is a mystery to me) then the galvanic corrosion risk was the same as not being hooked to a landline at all"

 

Therefore you agree that not bonding the earth to the hull greatly reduces the galvanic corrosion risk. You just have this bee in your inverter about drowning through electrical leakage. There is no example of this on the UK waterways. And if so, why are other mammals not beinbg decimated? - I have been on boats for a long time and have not noticed an undue amount of dogs, rats, voles or other mammalia drifting past.

 

I don't know what your interest is in trying to get this made a part of the BSS but I for one will not be thanking you if you succeed.

 

I think Gibbo conceeds that earth hull bonding increases the risk of galvanic corrosion. However, these are two separate issues. If one must do a risk comparison, then whilst the possibility of electrocution may be more remote, it's impact would be much greater.

 

Look up "double insulated" or "class II" equipment.

 

By definition it has 2 conductors not 3.

 

Gibbo

 

I see, thank you.

Edited November 17, 2006 by blackrose

[Gibbo]

OK, so I will be gently cooked due to being part of a series/parallel circuit with the water, which is of such a high resistance that the parallel bit of it will dump all the volt drop on me, but of such a low resistance that the drop between boat and me and me and canal bed is low.

I take no issue with the need for earth bonding but I am extremely dubious about this particular illustration, but then I am just the humble tradesman, only city and guilds, no letters after my name.

 

If you are so confident of this then why not actually try the challenge?

 

Gibbo, In my experience there are people with letters after their name, and people with shit under their fingernails, and each is useless at the others job. You seem to have achieved a crossover for which I congratulate you, but I think it unreasonable to assert that a technical argument is settled by comparing qualifications. I have been patronised so many times by graduates who smile at me indulgently whilst asserting the most astonishing rubbish.

 

There is, of course, a lot of truth in that.

 

But I'm still waiting for a valid argument that not bonding earth/hull is safter than bonding it.

 

Several valid arguments have been put forward that to bond is safer than not to bond. Yet none the other way round. Not a single one.

 

Gibbo

 

You originally wrote in the galvanic isolator soap opera to the effect that "if the earth was not bonded to the hull but simply returned through the shoreline (why that makes no sense to you is a mystery to me)

 

Because that isn't what you wrote and it wasn't in that context.

 

then the galvanic corrosion risk was the same as not being hooked to a landline at all"

 

Therefore you agree that not bonding the earth to the hull greatly reduces the galvanic corrosion risk.

 

 

Correct. I have never denied this.

 

 

You just have this bee in your inverter about drowning through electrical leakage. There is no example of this on the UK waterways.

 

 

And somehow that is evidence that it cannot and does not happen? Even though other countries do have reams of evidence that it has happened, many, many times.

 

And if so, why are other mammals not beinbg decimated? - I have been on boats for a long time and have not noticed an undue amount of dogs, rats, voles or other mammalia drifting past.

 

I have, sheep, cats, dogs, rabbits, fish, swans, ducks, you name it.

 

 

I don't know what your interest is in trying to get this made a part of the BSS

 

Nothing other than safety. What possible interest could I have in it? What possible interest other than safety could *anyone* have in it?

 

That would *seem* imply that you only do things if you have a vested interest in them. Why assume other people are the same?

 

but I for one will not be thanking you if you succeed.

 

That doesn't concern me in the least.

 

Gibbo

Edited November 17, 2006 by Gibbo

[miles beyond]

If you are so confident of this then why not actually try the challenge?

There is, of course, a lot of truth in that.

 

But I'm still waiting for a valid argument that not bonding earth/hull is safter than bonding it.

 

Several valid arguments have been put forward that to bond is safer than not to bond. Yet none the other way round. Not a single one.

 

Gibbo

 

...why are other mammals not beinbg decimated? - I have been on boats for a long time and have not noticed an undue amount of dogs, rats, voles or other mammalia drifting past....

 

I wrote. Come on then, explain it, and find a UK example of this new form of drowning that is relevant to our waterways.

 

Hooray for snibble. A person working at the sharp end of the stick instead of pontificating odd unsubstantiable theories.

[ChrisPy]

there are recognised industry standards for all this. Read the BSS chapter 3 introduction for example.

 

if certain folks think they are clever enough to recommend not following the standards, why don't they agitate to get on the BS/EN/ISO standards review bodies and revise the standards to their concept of greater safety......................

 

........................ no, I don't expect any replies, because there is no evidence that it is better not to bond.

 

I trust non-technical readers are not tempted to follow unproven advice in order to cut corners.

 

I suggest this thread should be closed, it's getting farcical.

[Chris Lingwood]

Right. OK another challenge.

 

I'll unearth my hull. I will then connect live to my hull simulating a fault. I'll stand there at 230v ac quite merrily. You can stand at 0v ac also merrily. You can then step on to my boat from the jetty......BANG! SIZZLE! OK rubber soles might save you but I'm sure sooner or later you'd find a way to touch the jetty and the hull at the same time.

 

 

 

OR more proof. Scale your boat down to the size of a microwave. Throw that useless earth wire away, we won't be needing that! Now connect the live to the metal casing of the microwave....do you want to touch it now? of course you don't, neither will you start shoving screw drivers into mains sockets. A boat in this respect is identical to all metal cased appliances, which, with our electrical system, needs to have an earth! Otherwise there is the risk of death!

[ChrisPy]

I will then connect live to my hull simulating a fault.

your RCD or the shore RCD will have tripped ages ago, no? ......................

Edited November 17, 2006 by chris polley

[miles beyond]

Right. OK another challenge.

 

I'll unearth my hull. I will then connect live to my hull simulating a fault. I'll stand there at 230v ac quite merrily. You can stand at 0v ac also merrily. You can then step on to my boat from the jetty......BANG! SIZZLE! OK rubber soles might save you but I'm sure sooner or later you'd find a way to touch the jetty and the hull at the same time.

OR more proof. Scale your boat down to the size of a microwave. Throw that useless earth wire away, we won't be needing that! Now connect the live to the metal casing of the microwave....do you want to touch it now? of course you don't, neither will you start shoving screw drivers into mains sockets. A boat in this respect is identical to all metal cased appliances, which, with our electrical system, needs to have an earth! Otherwise there is the risk of death!

Of course it needs an earth. That is through the landline. It doesn't need to be the hull