Earth/Hull bonding

[ChrisPy]

if anyone thinks water is a good conductor, try driving your car into the canal with the lights on and see how long it takes for the battery to run down or the fuses to blow. it could take hours.

 

....... no, I won't pay for your vehicle to be recovered from the cut.

 

 

 

 

 

on a similar topic, do you remember the silly luddites who used to preach that you shouldn't wear seat belts in a car because it made it more difficult to get out in the event the car caught fire. I expect the same people refuse to bond their hulls these days.

[Speedwell]

Chris,

Your experiment is too drastic for me so I tried multi meter prods in tap water. The resistance was much higher than I expected so I concede that it would be possible to get the hull live if the canal water were pure enough.

 

Gibbo

40000 sq ins is roughly the bottom area of a 50' narrowboat. You can scale it up or down as you wish depending on how much current you think can be transferred to the water. Even at 1 milliamp/sq in it's still a sizable current.

 

Arthur

[chris w]

Speedwell

 

Try the same experiment again and start adding impurities to get an idea of how the conductance of the water changes. Add dirt, pond water, bath water, salt etc. You'll be amazed at how non-conductive dirty water is. Salty water is much more conductive.

 

Chris

[miles beyond]

 

I could go on.

 

Gibbo

 

No disagreement there then.

[ChrisPy]

No disagreement there then.

m.b.,

at last you've managed to make me smile ........................

[Gibbo]

Gibbo

40000 sq ins is roughly the bottom area of a 50' narrowboat. You can scale it up or down as you wish depending on how much current you think can be transferred to the water. Even at 1 milliamp/sq in it's still a sizable current.

 

Arthur

 

I didn't ask what the surface area of the bottom plate was. I asked where you got that arbitrary number of 1 amp/sq in

 

Gibbo

 

No disagreement there then.

 

Yet it still doesn't sink in with some people.

 

Gibbo

[Speedwell]

I didn't ask what the surface area of the bottom plate was. I asked where you got that arbitrary number of 1 amp/sq in

Gibbo

It's exactly that - an arbitrary number for you to scale from depending on what you think the flow would be.

On another of your points, the iron oxide (mill scale) on the bottom of boats would weather to rust in a few years. Rust is mainly hydrated ferric hydroxide and is very porous so for practical purposes the steel in the bottoms of most (older) boats would be wetted. In any case most boats have an easy passage for electricity into the water via the anodes and perhaps the prop shaft and prop. It's the conductivity of the water and the surrounding earth that counts and I have already agreed that this is lower than the results of dropping the end of my wander lead into the cut and pouring tap water on electrical apparatus had led me to expect. (Only once each so not statistically valid)

Arthur

[tomsk]

It's exactly that - an arbitrary number for you to scale from depending on what you think the flow would be.

On another of your points, the iron oxide (mill scale) on the bottom of boats would weather to rust in a few years. Rust is mainly hydrated ferric hydroxide and is very porous so for practical purposes the steel in the bottoms of most (older) boats would be wetted. In any case most boats have an easy passage for electricity into the water via the anodes and perhaps the prop shaft and prop. It's the conductivity of the water and the surrounding earth that counts and I have already agreed that this is lower than the results of dropping the end of my wander lead into the cut and pouring tap water on electrical apparatus had led me to expect. (Only once each so not statistically valid)

Arthur

 

Has Chris w got a veiw? I would be most bored to tears interested to hear his portentious comments

[Speedwell]

Speedwell

Try the same experiment again and start adding impurities to get an idea of how the conductance of the water changes. Add dirt, pond water, bath water, salt etc. You'll be amazed at how non-conductive dirty water is. Salty water is much more conductive.

Chris

I do know this. What I found hard to imagine was that the canal water would be clean enough to prevent at least a low current density to pass.

Arthur

[Gibbo]

It's the conductivity of the water and the surrounding earth that counts

 

Actually it is the conductivity of the interface between the hull and the water that is most important.

 

Try to calculate the resisitance of a sphere of steel and you'll understand why.

 

Gibbo

[miles beyond]

It has been a fascinating debate.

 

I have been referred to both as a fool and a Luddite for suggesting that bonding the AC earth to the hull is not a good idea. I would add that I am not the person who emailed Gibbo "off forum".

 

I will summarise:

 

1. It is readily admitted in two fora (both this and the Galvanic Isolator debate) - that in bonding the AC earth to the hull you create a greatly increased risk of galvanic corrosion.

 

2. That the first worry about not bonding earth to hull is based upon the idea that if your double skinned ring main, or a 230v appliance attached to it, somehow shorts to the hull without tripping the boat RCD then a person touching both boat and shore will be electrocuted. Even if the RCD has not triped then it is more likely they will jump back and go "Jesus ****", rather than die.

 

3. That even a small leakage to the hull that would be insufficient to trip the RCD may paralyse a nearby person floating in the water resulting in their drowning.

 

Readers can make their own minds up.

 

!. Unarguable.

 

2. The best argument to this I have read is that your RCD may not be functioning properly. A good case for ensuring on a regular basis that it does. Otherwise every land-based dwelling might as well give up with them and have an isolation transformer instead as well.

 

3. The incidence of such drowning is based upon some internet information and is not with empirical foundation. Gibbo has been unable and/or unwilling to provide an example of this in the UK, and frankly this is unproven X files stuff that should be treated with a high degree of circumspection.

 

Fool? This stemmed from a comment by Snibble who posted to the effect that no fool wold not earth their AC properly. Quite so. I Make sure my boat when connected to a landline is properly earthed. I see no need to make the hull part of that equation as it is not, and cannot be, without tripping the RCD, a part of that equation. Plainly you need to assess what appliances are on your boat and how they are connected. Mine are a washing machine (non-conductive plastic flexible hoses), a microwave (standard three pin plug) and occasionally, too occasionally, a vacuum cleaner. That's it. Bear in mind that I am the fool who most frequently gets on and off my boat.

 

Luddite? Ned Ludd and his followers went around smashing up farm machinery as industrialisation was making thousands of agricultural workers redundant and consigning them to poverty. I am neither smashing up anything nor filled wih the belief that GIs and ITs are the way forward. So while I may believe that there has yet to be a decent case for bonding the AC earth to the hull and spending hundred of pounds addressing the consequences (of which this topic makes it plain are highly uncertain yet expensive solutions), I do not think there is any case to be made for bonding the English language to gobbledygook.

 

Both Gibbo and Chris W are plainly well versed in their field. They inhabit a world of electrical knowledge that I have never landed on, but I worry about being cornered in a party by such persons. "Fancy a dance?" "Not until I've explained Ohm's principle to you at some length." But that does not mean that some of the rest of us cannot blow away the obfuscation and look at the simple process of ensuring that our boats are more than adequately protected by an earth connection to land without involving the hull.

 

And it is only 28 shopping days to Christmas, or in the language of this forum, 32kVA where x = q/21mW if v is constant K.

[tomsk]

It has been a fascinating debate.

 

I have been referred to both as a fool and a Luddite for suggesting that bonding the AC earth to the hull is not a good idea. I would add that I am not the person who emailed Gibbo "off forum".

 

I will summarise:

 

1. It is readily admitted in two fora (both this and the Galvanic Isolator debate) - that in bonding the AC earth to the hull you create a greatly increased risk of galvanic corrosion.

 

2. That the first worry about not bonding earth to hull is based upon the idea that if your double skinned ring main, or a 230v appliance attached to it, somehow shorts to the hull without tripping the boat RCD then a person touching both boat and shore will be electrocuted. Even if the RCD has not triped then it is more likely they will jump back and go "Jesus ****", rather than die.

 

3. That even a small leakage to the hull that would be insufficient to trip the RCD may paralyse a nearby person floating in the water resulting in their drowning.

 

Readers can make their own minds up.

 

!. Unarguable.

 

2. The best argument to this I have read is that your RCD may not be functioning properly. A good case for ensuring on a regular basis that it does. Otherwise every land-based dwelling might as well give up with them and have an isolation transformer instead as well.

 

3. The incidence of such drowning is based upon some internet information and is not with empirical foundation. Gibbo has been unable and/or unwilling to provide an example of this in the UK, and frankly this is unproven X files stuff that should be treated with a high degree of circumspection.

 

Fool? This stemmed from a comment by Snibble who posted to the effect that no fool wold not earth their AC properly. Quite so. I Make sure my boat when connected to a landline is properly earthed. I see no need to make the hull part of that equation as it is not, and cannot be, without tripping the RCD, a part of that equation. Plainly you need to assess what appliances are on your boat and how they are connected. Mine are a washing machine (non-conductive plastic flexible hoses), a microwave (standard three pin plug) and occasionally, too occasionally, a vacuum cleaner. That's it. Bear in mind that I am the fool who most frequently gets on and off my boat.

 

Luddite? Ned Ludd and his followers went around smashing up farm machinery as industrialisation was making thousands of agricultural workers redundant and consigning them to poverty. I am neither smashing up anything nor filled wih the belief that GIs and ITs are the way forward. So while I may believe that there has yet to be a decent case for bonding the AC earth to the hull and spending hundred of pounds addressing the consequences (of which this topic makes it plain are highly uncertain yet expensive solutions), I do not think there is any case to be made for bonding the English language to gobbledygook.

 

Both Gibbo and Chris W are plainly well versed in their field. They inhabit a world of electrical knowledge that I have never landed on, but I worry about being cornered in a party by such persons. "Fancy a dance?" "Not until I've explained Ohm's principle to you at some length." But that does not mean that some of the rest of us cannot blow away the obfuscation and look at the simple process of ensuring that our boats are more than adequately protected by an earth connection to land without involving the hull.

 

And it is only 28 shopping days to Christmas, or in the language of this forum, 32kVA where x = q/21mW if v is constant K.

 

Funny as F*** , Have a beeer

[miles beyond]

Funny as F*** , Have a beeer

Glass of vino plonko coming up. Cheers!

[tomsk]

Glass of vino plonko coming up. Cheers!

 

You earnt it Bucko!! Have another on me

[grunders]

WOW!!!

 

Just read the whole topic....didn't understand a thing.

 

But it must be about something important as everyone seems to have an opinion.

 

Oh well, never mind.

[blackrose]

Miles, I don't think there's any excuse for the personal attacks directed at you. I am a non-technical person myself, but it seems to me that in the (however unlikely) event of a short to the hull, your setup relies completely on the RCD working correctly. How often do you test it?

Edited November 24, 2006 by blackrose

[ChrisPy]

....................... excuse me while I YAWWWWWWN

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

...... are we really going to go round in ever-increasing circles on this one?

[tomsk]

....................... excuse me while I YAWWWWWWN

...... are we really going to go round in ever-increasing circles on this one?

 

 

It really is the only way forward

[Tommo]

, but it seems to me that in the (however unlikely) event of a short to the hull, your setup relies completely on the RCD working correctly. How often do you test it?

 

As it does in many domestic situations with no problem.

 

Tommo

[chris w]

it seems to me that in the (however unlikely) event of a short to the hull, your setup relies completely on the RCD working correctly. How often do you test it?

 

One thing to bear in mind as well is that pressing the RCD test button ONLY tests the actual internals of the RCD. It does NOT test that your wiring is correct such that a real earth fault would actually trip the RCD.

 

Chris

[Gibbo]

One thing to bear in mind as well is that pressing the RCD test button ONLY tests the actual internals of the RCD. It does NOT test that your wiring is correct such that a real earth fault would actually trip the RCD.

 

Chris

 

Also don't forget that RCDs on marina shorepower outlets are NOT mandatory. If the fault ocurrs before the boat RCD (assuming one is fitted and working) then the same problem results.

 

A problem which bonding earth/hull would have prevented.

 

Gibbo

[miles beyond]

Miles, I don't think there's any excuse for the personal attacks directed at you. I am a non-technical person myself, but it seems to me that in the (however unlikely) event of a short to the hull, your setup relies completely on the RCD working correctly. How often do you test it?

Not often enough I suppose from having been involved in this malarky! You are right, but so many things we do rely upon we should test and check with greater attention than we sometimes give them.

 

I have had boats for 30 years - lived on them for much of that time - and I hate to see a simple wonderful way of life get buried. Especially by those who defend their opinions not with practical experience, but by waving their qualifications at us.

 

 

....................... excuse me while I YAWWWWWWN

...... are we really going to go round in ever-increasing circles on this one?

 

So why did you bother to reply then? You had more than enough to say earlier when you were renting an apartment up Gibbo's backside.

[blackrose]

As it does in many domestic situations with no problem.

 

Tommo

 

In many domestic situations one isn't climbing in and out of a metal box.

 

So why did you bother to reply then? You had more than enough to say earlier when you were renting an apartment up Gibbo's backside.

 

Perhaps I was mistaken earlier when I said there were no excuses for anyone directing personal attacks at you?

[ChrisPy]

Perhaps I was mistaken earlier when I said there were no excuses for anyone directing personal attacks at you?

[Gibbo]

But that does not mean that some of the rest of us cannot blow away the obfuscation and look at the simple process of ensuring that our boats are more than adequately protected by an earth connection to land without involving the hull.

 

 

Except that

 

1) You clearly do not understand the subject with sufficient depth of knowledge to even summarise correctly.

2) Your conclusions are incorrect.

3) If someone dies as a result of your "technical advice" I will be the first to blow the whistle.

4) People who have no clue about electricity and it's dangers have no right spouting what are nothing more than opinions with *no* technical backing on a public forum.

 

Gibbo