Shore power earth

[GEB]

That looks like TN-S as you said.

The cut-out (cream unit) is an old type and so probably not the sort usable for TN-C-S. If you had this system there should be a label stating that you are connected to Protective Multiple Earthing (PME).

It has been known for some 'electricians' to do a DIY PME connection (earth to neutral) - this is very dangerous as the supply network requirements for PME are very different. It may be that he was removing something like that.

Check with your supplier if you have any doubts - they should really have upgraded that cut-out by now.

 

[VicS]

That looks like TN-S as you said.

The cut-out (cream unit) is an old type .............
Check with your supplier if you have any doubts - they should really have upgraded that cut-out by now.

 

[GEB]

It looks like a more modern one in that view - is it all plastic ?

 

[VicS]

It looks like a more modern one in that view - is it all plastic ?

Yes. I guess it and the board date from the early 1960s. Everything else is more recent

 

[GEB]

In that case they probably would not change it.

 

[VicS]

In that case they probably would not change it.

Well thats the house earthing sorted. Now we can get back to the OP's old Spanish boat and the dodgy Spanish electricity supply

 

[danielefua]

Many countries use double pole switching for isolation and control and as such are not really worried about polarity. Their regulations will require correct polarity but it is often ignored as, for them, there is no real risk.

This along with what you write later i.e. "TN-C-S is not permitted on the supplies to boats or caravans (it is actually illegal by statute)" confirms what I wrote before although none considered it: while on shore power, relying on the harmlessness of a "neutral" is mindless.
I am sorry but although I agree with most of what VicS writes I disagree when he states "don't worry about connecting it (the local ground cable) to the planet's surface". The ground wire of the shore power should not be trusted and not connected to the boat ground circuit but the latter should be connected to a ground plate in contact with the water or to a buried rod when on hard.

Of course the availability of an isolation transformer makes a total different story.

Daniel

 

[VicS]

This along with what you write later i.e. "TN-C-S is not permitted on the supplies to boats or caravans (it is actually illegal by statute)" confirms what I wrote before although none considered it: while on shore power, relying on the harmlessness of a "neutral" is mindless.
I am sorry but although I agree with most of what VicS writes I disagree when he states "don't worry about connecting it (the local ground cable) to the planet's surface". The ground wire of the shore power should not be trusted and not connected to the boat ground circuit but the latter should be connected to a ground plate in contact with the water or to a buried rod when on hard.

Of course the availability of an isolation transformer makes a total different story.

Daniel

my refernce to not connecting it to the planet's surface was when using an isolation transformer when such a connection would serve little useful purpose

As I see it there are two alternative

1. To use an isolation transformer, create an internal "protective conductor" system with equipotential bonding of all the relevant items on board. Keep the boat electrically isolated from all else.​

2. To have no isolation transformer but to have a shorepower supply with a good, reliable, low resistance earth connection which can then be connected to the boat's own protective conductor system. I am uneasy about doing this by using a ground plate and connection through the water. I fear that this could contribute to all the mythical stray currents that apparently infest marinas and could, esp in fresh or brackish water, put people in the water at risk

Obviously a ground stake is impractical, so if the shorepower earth is suspect an isolation transformer is the only acceptable option.
​

Regarding a TN-C-S system ... obviously unsuitable and potentially dangerous with temporary connections where the polarisation can and does become reversed. Not quite sure how this crept into the discussion on boat earthing

 

[ianabc]

On a steel hull

On my steel boat I do have my mains connected to the steel hull and thus all metal cased appliances.

My DC negative is insulated from the hull as is my engine.

If there is no negative ground from the battery bank to the hu

if there is a short circuit the

breakers will not trip!


We have double breakers on each circuit and a 12 volt ground to the hull.

That is, we do now...

Had discussion with 2 marine engineers ( University graduate engineers, one an engineering officer in the Coast Guard and the other worked on offshore oil rigs - electrical engineer with 2 degrees. Both experienced hands on workers. Both examined my steel vessel.

Both confirm that you do need a 12 volt negative ground.

Interestingly some commercial and Coastguard vessels have a hull fault detector, that consists of a flashing light that stops flashing, if and when, a hull fault is detected.

 

[mcframe]

Can be done with a neon from live to earth. A second from neutral to earth will also help confirm neutral live polarisation is correct.

A socket tester that plugs into a 13 amp socket probably the most sensible way to go.
Only a few £s from any DIY store..

https://www.google.co.uk/search?q=s...=X&ei=3jkFVdGmM4T5UMHagOAC&sqi=2&ved=0CFEQsAQ


Neither is a foolproof way of confirming a good low resistance earth connection though


Probably best not to leave either type on/ plugged in if you have a galvanic isolator as the current flow to earth will propbably overide its function and render it uselss a preventing corrosion

I keep one of those plugged into one of my mains sockets, next to the chart table. Whenever I connect shore power, I flick it on for a quick check.
(Faster than opening locker to check for green light on RCD'd combo consumer unit/charger - with galvanic isolator.)

Also handy for checking extension leads OnceEverySoOften.

 

[VicS]

If there is no negative ground from the battery bank to the hu

if there is a short circuit the

breakers will not trip!

If a circuit is protected by an overcurrent circuit breaker it will trip in the event of a short circuit occurring in that circuit whether or not the negative is grounded

We have double breakers on each circuit and a 12 volt ground to the hull.

That is, we do now..

why double breakers ?

Had discussion with 2 marine engineers ( University graduate engineers, one an engineering officer in the Coast Guard and the other worked on offshore oil rigs - electrical engineer with 2 degrees. Both experienced hands on workers. Both examined my steel vessel.

Both confirm that you do need a 12 volt negative ground.

Some engine installations have an isolated electrical system. Often to avoid corrosion of sail drive legs. In those situations it is not appropriate to ground the DC negative. The vessel will have what is described as a "Fully insulated 2 wire DC system".

You should study, and draw the attention of your 2 University graduate marine engineers to, the International Standard for Extra-low-voltage d.c. installations in small craft; ISO 10133

Interestingly some commercial and Coastguard vessels have a hull fault detector, that consists of a flashing light that stops flashing, if and when, a hull fault is detected.

 

[danielefua]

You should study, and draw the attention of your 2 University graduate marine engineers to, the International Standard for Extra-low-voltage d.c. installations in small craft; ISO 10133

VicS, you are great!!! ...and I mean it!

Daniel

 

[rogerthebodger]

If there is no negative ground from the battery bank to the hu

if there is a short circuit the

breakers will not trip!

If you are taking about a current overload breaker there tand to be single pole on 12VDC circuits as double pole are overkill and unnecessary.

We have double breakers on each circuit and a 12 volt ground to the hull.

Total overkill and totally unnecessary. The DC negative connection to metal hull can cause stray currents and induce increase anode wasting.

That is, we do now...

Had discussion with 2 marine engineers ( University graduate engineers, one an engineering officer in the Coast Guard and the other worked on offshore oil rigs - electrical engineer with 2 degrees. Both experienced hands on workers. Both examined my steel vessel.

Both confirm that you do need a 12 volt negative ground.

Well if you want to get into a pissing contest I have a degree in engineering from a UK University MIMechE and C Eng, worked in both Mechanical and Electrical Design for 20 odd years before moving into PLC and microprocessor engineering control systems. Been playing with Boats of all kinds for 40 years now.

Interestingly some commercial and Coastguard vessels have a hull fault detector, that consists of a flashing light that stops flashing, if and when, a hull fault is detected.

Interesting , what type of fault is the above device detecting. I have shore power reverse polarity and shore power earth fault detector. The mains incoming earth line is connected to my hull through a GI but the 12VDC negative is not connected to my hull at any point. Even my engine is isolated from the steel through flexible mountings and coupling. Even the engine and gearbox control cables are isolated from the engine.

My anodes are working as there is some pitting on the surface but have no major wasting over the last 5 years.

How long do your anodes last.

 

[GEB]

"Interesting , what type of fault is the above device detecting."

That sounds like an on board I.T system (not earthed) - not related to shore supply.

It would be detecting a first fault condition. It is a common system on ships - particularly for things like steering gear. It does not allow a fault to 'earth' (the hull in this case) to cause automatic disconnection as the result of this might be unexpected steering loss.

The worst that can happen is that the steering gear catches fire, but if you disconnect it without warning the ship could broach roll over and sink - however, look on the bright side - at least the fire would go out

 

[danielefua]

Obviously a ground stake is impractical, so if the shorepower earth is suspect an isolation transformer is the only acceptable option.

In theory you are right but practically (I think of my own experience around in Europe) shorepower earth and neutral are "always" suspect; therefore the following are the optimal options:

1) Old fashion passive isolation transformers: weight 25-30 kg depending on power, cost affordable
2) Active high frequency isolation transformers: weight 10 kg, cost: way too high for my pocket!

Not having an ocean liner, my choice untill I can afford a modern low weight IT is: shore ground wire disconnected at the shore power socket onboard, not relying on the "neutrality" of any of the two wires, RCD, two pole switches for all high voltage appliances, and an inboard ground wire circuit connected to a good plate outboard. All high voltage appliances have their reachable metal parts connected only to the inboard ground wire.

I don't think I am endangering any diver more than endangering myself when I use shore power and any stray current should be promptly detected by the RCD which, hopefully, is doing its job. I acknowledge it is not the optimum but it is an acceptable and safe compromise.

Daniel

PS just a note. Every time the "ground wire" topic appears in a forum, instantly thousands of Electric Engineers pop up from nowhere and the thread becomes infinite. Interesting anthropological subject...

 

[westernman]

In theory you are right but practically (I think of my own experience around in Europe) shorepower earth and neutral are "always" suspect; therefore the following are the optimal options:

1) Old fashion passive isolation transformers: weight 25-30 kg depending on power, cost affordable
2) Active high frequency isolation transformers: weight 10 kg, cost: way too high for my pocket!

Not having an ocean liner, my choice untill I can afford a modern low weight IT is: shore ground wire disconnected at the shore power socket onboard, not relying on the "neutrality" of any of the two wires, RCD, two pole switches for all high voltage appliances, and an inboard ground wire circuit connected to a good plate outboard. All high voltage appliances have their reachable metal parts connected only to the inboard ground wire.

I don't think I am endangering any diver more than endangering myself when I use shore power and any stray current should be promptly detected by the RCD which, hopefully, is doing its job. I acknowledge it is not the optimum but it is an acceptable and safe compromise.

Daniel

PS just a note. Every time the "ground wire" topic appears in a forum, instantly thousands of Electric Engineers pop up from nowhere and the thread becomes infinite. Interesting anthropological subject...

According to my current understanding of these things, this would also be my choice of how to do it. Also I think I would also connect the DC negative at one place to the same place as the inboard AC ground wire.

 

[VicS]

Also I think I would also connect the DC negative at one place to the same place as the inboard AC ground wire.

Yes this is the correct thing to do, except of course when the DC system is fully isolated as is the case with some engine/saildrive combinations. See the latest edition of ISO 13297 for details

 

[GEB]

I invite you both to view a quick calculation.

Let the impedance of the line conductor from the supply transformer to some Class 1 (earthed metal) appliance on your vessel be R1.

Let the impedance from your earth plate to the source of supply be R2.

R1 may be < 1 ohm.

R2 is difficult to define but most of the impedance is likely to be between the earth plate and the shore - assume it is 100 ohms.

Now assume a zero impedance fault in the appliance causes a short between the line conductor and your protective conductor (connected to you earth plate). A kettle element failure will often produce these conditions.

The touch voltage on your earth plate during the time it takes for a fault to clear is given by:

Vt = Vo * R2/R1 + R2

Assume Vo is 230 volts

Touch voltage = 100/1 + 100 = 228 volts

Of course if the RCD is slow or worse fails to open this voltage will exist for a considerable time.

Any divers in the water may get very cross.

It is a requirement of ISO 13297 : 2012 Small craft — Electrical systems — Alternating current
installations - regulation 4.2 that you connect the shore circuit protective conductor to your system.

This will considerably reduce the touch voltage on your earth plate.

 

[colind3782]

PS just a note. Every time the "ground wire" topic appears in a forum, instantly thousands of Electric Engineers pop up from nowhere and the thread becomes infinite. Interesting anthropological subject...

I got a headache 40 posts ago! Wish I hadn't said anything now

 

[danielefua]

I invite you both to view a quick calculation.

Let the impedance of the line conductor from the supply transformer to some Class 1 (earthed metal) appliance on your vessel be R1.

Let the impedance from your earth plate to the source of supply be R2.

R1 may be < 1 ohm.

R2 is difficult to define but most of the impedance is likely to be between the earth plate and the shore - assume it is 100 ohms.

Now assume a zero impedance fault in the appliance causes a short between the line conductor and your protective conductor (connected to you earth plate). A kettle element failure will often produce these conditions.

The touch voltage on your earth plate during the time it takes for a fault to clear is given by:

Vt = Vo * R2/R1 + R2

Assume Vo is 230 volts

Touch voltage = 100/1 + 100 = 228 volts

Of course if the RCD is slow or worse fails to open this voltage will exist for a considerable time.

Any divers in the water may get very cross.

It is a requirement of ISO 13297 : 2012 Small craft — Electrical systems — Alternating current
installations - regulation 4.2 that you connect the shore circuit protective conductor to your system.

This will considerably reduce the touch voltage on your earth plate.

Although your calculation are rather pessimistic, they are irrefutable.

It is probably true that "a requirement of ISO 13297 : 2012 Small craft — Electrical systems — Alternating current installations - regulation 4.2 that you connect the shore circuit protective conductor to your system" but it is also true that there must be some directive that requires that a shore circuit protective conductor exists indeed.
According to my experience, tha latter directive is often disregarded. Moreover, as far as I know, if you have an isolation transformer the directive cited by you can and should be disregarded.

Daniel