Earthing boat electric systems

[RobertN]

I have a Victron 12/3000/120 unit and intend to use AC for domestic appliances and 12v for lighting. How do I earth these systems. i.e. What do I actually do?

 

Thanks

 

Robert

[steelaway]

I have a Victron 12/3000/120 unit and intend to use AC for domestic appliances and 12v for lighting. How do I earth these systems. i.e. What do I actually do?

 

Thanks

 

Robert

 

 

Hi There

 

I asked the same question and now I am safe.

I also made up the tester plug as suggested and that now trips the fuse immedietly

 

See ---- http://www.canalworld.net/forums/index.php...amp;hl=earthing

 

Alex

[FORTUNATA]

Normally, steel boat electrics are isolated from the hull so the circuits are earthed to the negative battery terminals. It's also important current doesn't leak to the hull from any closed electrical system.

 

I have a Victron 12/3000/120 unit and intend to use AC for domestic appliances and 12v for lighting. How do I earth these systems. i.e. What do I actually do?

 

Thanks

 

Robert

[Tony Brooks]

I have a Victron 12/3000/120 unit and intend to use AC for domestic appliances and 12v for lighting. How do I earth these systems. i.e. What do I actually do?

 

Thanks

 

Robert

 

 

In view of what always get said in this particular topic I would advise that you get your local library to get you a copy of the latest British Marine Electrical Association codes of practise. This will answer your question and they are based on BS & ISO standards.

 

By doing this you will be able to sort the good advice from bad and possible avoid future injury and possible insurance problems.

 

Keep watching and you will almost certainly find you get about three views expressed but only one complies with the BMEA Codes.

[Chris Pink]

Normally, steel boat electrics are isolated from the hull so the circuits are earthed to the negative battery terminals. It's also important current doesn't leak to the hull from any closed electrical system.

 

oh dear oh dear, now what have you done.....

 

......unleashed the furies, i expect.

[tidal]

INCOMING

 

[Gibbo]

Normally, steel boat electrics are isolated from the hull so the circuits are earthed to the negative battery terminals. It's also important current doesn't leak to the hull from any closed electrical system.

 

If you have a permanent (in for Chris Pink's benefit) AC electrical installation isolated from the hull then in Europe (and most of the rest of the world) you are in breach of every single guideline and regulation that exists.

 

If someone got electrocuted as a result of such an installation I don't see any reason why manslaughter charges wouldn't or couldn't be brought against the culprit.

 

Gibbo

Edited August 19, 2008 by Gibbo

[Chris Pink]

If you have a permanent (in for Chris Pink's benefit) AC electrical installation

 

most kind, most kind.

[dor]

As I understand it the 12V DC negative should be earthed to a labelled earth stud on the shell. The 230V AC earth, whether from a shore line or inverter, should also be linked, through an isolation transformer or galvanic isolator if desired, to a labelled stud also. There is some difference of opinion amongst the experts as to whether this should be the same stud or whether there should be two close, but separate, studs.

 

Without this earth bonding to the hull, the RCD may not trip and it could also create a lethal hazard to people outside the boat or in the water.

[magnetman]

it used to be okay to use a flower pot for earth requirements aboard vessels but due to legislation i believe a growbag is now more acceptable.

[blackrose]

it used to be okay to use a flower pot for earth requirements aboard vessels but due to legislation i believe a growbag is now more acceptable.

 

If someone actually does this you could face manslaughter charges too!

[ChrisPy]

There is some difference of opinion amongst the experts as to whether this should be the same stud or whether there should be two close, but separate, studs.

apart from the saving of the cost of one stud , can anyone give me a good reason why he would ever consider bringing the 12V negative and the mains earth together on one stud?

 

If someone got electrocuted as a result of such an installation I don't see any reason why manslaughter charges wouldn't or couldn't be brought against the culprit.

I s'pose if the electrocution wasn't actually terminal (no pun intended) the culprit might get away with a reckless wiring and attempted manslaughter charge

[magnetman]

Out of interest, has anyone actually been killed or seriously injured by stepping on or off a boat with inadequate earthing?

[bottle]

Whether anyone has died does not matter, there is the potential (pun intended ) for them to.

[Justme]

can anyone give me a good reason why he would ever consider bringing the 12V negative and the mains earth together on one stud?

 

Electricaly is they any real difference between the two cables being on one stud or at each end of the boat?

 

Cant see the resistance being that high from one end of the boat to the other let alone between two studs prob in the engine bay.

 

 

Justme

[MoominPapa]

Electricaly is they any real difference between the two cables being on one stud or at each end of the boat?

 

Cant see the resistance being that high from one end of the boat to the other let alone between two studs prob in the engine bay

The reason for using two studs is to eliminate the failure mode where the stud becomes detached from the Hull, but the DC and AC cables are still connected together because they're still attached to the stud. If that happens and then there's an AC earth fault (ie a live cable touches the hull) then the fault current will get as far as the DC negative system and then find its way to the hull via any stray negative-to-hull connections. This leads to "interesting" effects like the braid of the co-axial cable of the radio aerial glowing red hot.

 

The reason for having only one connection to the hull is to make sure that the electrical system cannot create a current flowing through the hull. The hull has low resistance, but not zero resistance, and the water has high resistance but not infinite resistance. This means that a very small proportion of any current flowing in the hull will infact leave the hull, flow through the water and then re-enter the hull. That causes electrolysis which causes corrosion.

 

The best compromise for these two competing requirements is two studs, mechanically distinct, but very close to each other on the steelwork.

 

MP.

[Justme]

The reason for using two studs is to eliminate the failure mode where the stud becomes detached from the Hull, but the DC and AC cables are still connected together because they're still attached to the stud. If that happens and then there's an AC earth fault (ie a live cable touches the hull) then the fault current will get as far as the DC negative system and then find its way to the hull via any stray negative-to-hull connections. This leads to "interesting" effects like the braid of the co-axial cable of the radio aerial glowing red hot.

 

 

In the above example I would expect that the current would go from the live mains via the fault to the hull from the hull to the engine via its earth strap or control cables, drive line, pipes etc then the batts neg terminal to the earth (still connected via the single free floating stud) of the mains system & trip the RCD?

 

In a two stud system & the mains earth comes off you could have a fault with a live boat as the return path is broken so the RCD will not trip.

 

I guess then what should be done is to have multipul mains earth to hull bonding points but still using a single cable run with no breaks. Similar to the earth bonding now done in houses to all touchable metal objects.

 

Justme

 

PS have had a few cars that have used the old fashioned choke cable as an engine earth return when the engine earth strap had failed due to corrosion.

[FORTUNATA]

If you wish to read up on arguments for earthing systems on steel boats, get a copy of John C Payne's Marine Electrical Electronics Bible where he dedicates chapters to each theme. This guy had some involvement in the dreaded Richard Branson's boat (don't mention Virgin, please ).

I just looked up the chapter on grounding and he says run the negative to an engine ground. Somewhere I seem to recall reading about differences between grounding on steel as opposed to fibreglass in this book but I'll have to try and find out where.

Where I may have got mixed up somewhere in the book is over stray current and corrosion. Give me some time and I'll re-read some of the information.

 

If you have a permanent (in for Chris Pink's benefit) AC electrical installation isolated from the hull then in Europe (and most of the rest of the world) you are in breach of every single guideline and regulation that exists.

 

If someone got electrocuted as a result of such an installation I don't see any reason why manslaughter charges wouldn't or couldn't be brought against the culprit.

 

Gibbo

[FORTUNATA]

I found it on page 98, He calls it the "two wire insulated return system", as opposed to what he then next describes as the "insulated return, one pole grounded." However, this book was mainly targeted at marine vessels and not inland waterways (hence the odd reference to Richard Branson).

I'm only studying this stuff at present so will keep an open mind once I get as much input as I can. It could be John C Payne is actually wrong but he can be contacted via his website.

 

If you have a permanent (in for Chris Pink's benefit) AC electrical installation isolated from the hull then in Europe (and most of the rest of the world) you are in breach of every single guideline and regulation that exists.

 

If someone got electrocuted as a result of such an installation I don't see any reason why manslaughter charges wouldn't or couldn't be brought against the culprit.

 

Gibbo

[Guest TerryL]

In view of what always get said in this particular topic I would advise that you get your local library to get you a copy of the latest British Marine Electrical Association codes of practise. This will answer your question and they are based on BS & ISO standards.

 

By doing this you will be able to sort the good advice from bad and possible avoid future injury and possible insurance problems.

 

Keep watching and you will almost certainly find you get about three views expressed but only one complies with the BMEA Codes.

 

Hi Tony, The British Marine Electrical Association doesn't exist! It's the British Marine Electronics Association and as such are biased in another direction and their code of practice is not in my opinion a great authority on mains supply electrics or compatability with the IET regulations which conflict, or their trade members conflict, with earthing of isolation transformers and the use of galvanic isolators. The ISO standards are also very limited. As an old electrician I'd much rather follow the IET regulations which are considered to be the standard than a trade associations code of practice, they might change it to suit their products!

 

On board mains electricity must be earthed to the hull or main earthing point not only from the onboard supplies (which includes the neutral) but uninterrupted from the shore unless a double insulated or shore based isolation transformer is used. An rccd must also be installed on shore and on board, the latter being a of a lower trip rate if possible. Battery electrics should be two wire and can also be earthed to the hull but should not use the same earth terminal which could compromise one or the other if loose or being worked on. If in doubt get an electrician in, he will have more knowledge of complicated safety regulations.

 

Terry

[ChrisPy]

I guess then what should be done is to have multipul mains earth to hull bonding points but still using a single cable run with no breaks. Similar to the earth bonding now done in houses to all touchable metal objects.

Just had a new kitchen installed at home. Electrician used the latest IEE regs which have apparently dropped this requirement ............. I don't know the background.

[Justme]

Just had a new kitchen installed at home. Electrician used the latest IEE regs which have apparently dropped this requirement ............. I don't know the background.

 

 

Why does that not suprise me lol

 

Justme

[Theo]

Out of interest, has anyone actually been killed or seriously injured by stepping on or off a boat with inadequate earthing?

 

A young swimmer was killed when approaching, not touching, a boat in an American Marina. There was a thread about this when I first joned the forum.

 

N

[MoominPapa]

In the above example I would expect that the current would go from the live mains via the fault to the hull from the hull to the engine via its earth strap or control cables, drive line, pipes etc then the batts neg terminal to the earth (still connected via the single free floating stud) of the mains system & trip the RCD?

 

They're also possibilties. There may be enough current to weld the control cables, or worse, the thrust bearing in the gearbox.

In a two stud system & the mains earth comes off you could have a fault with a live boat as the return path is broken so the RCD will not trip.

 

I guess then what should be done is to have multipul mains earth to hull bonding points but still using a single cable run with no breaks. Similar to the earth bonding now done in houses to all touchable metal objects.

 

Justme

 

PS have had a few cars that have used the old fashioned choke cable as an engine earth return when the engine earth strap had failed due to corrosion.

It's the same principle here, but with 240v around much more potentially dangerous. The biggest danger, pre-RCD, was that the total resistance of the circuit via the earthed hull was too high for the fuse to blow. That could lead to kilowatts being disipated in unlikely and dangerous places and shock hazards that didn't get disconnected. In the era of the compulsory RCD, the dangers of a high-impedance earth are less.

 

MP.

[Chris Pink]

If in doubt get an electrician in, he will have more knowledge of complicated safety regulations.

 

Very sound advice, however one of the reasons for the continuing re-emergence is the absence of regulation rather there are several (occasionally conflicting) sets of guidelines.