Shore power earth

[BabaYaga]

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.

A system not unlike the above has recently been suggested here, by a committee formed by boating organizations and authorities, as a way of avoiding the need for an isolation transformer but still meeting the ISO directive. However, with two important additions:
1) There must be an easy and obvious way of connecting the on board protective ground wire to the shore side ground wire when the boat is on the hard.
2) It is adviced to use a RCD with a 10 mA threshold instead of the more common 30 mA. This is for increased personal safety reasons.

 

[VicS]

Moreover, as far as I know, if you have an isolation transformer the directive cited by you can and should be disregarded.

Daniel

What GEB is describing, and doing the maths for is a situation where there is direct connection to the shoreside electricity supply. It is not valid or applicable to a system involving an isolation transformer.

 

[VicS]

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

Its not over yet. Better send out for another pack of aspirin!

 

[danielefua]

A system not unlike the above has recently been suggested here, by a committee formed by boating organizations and authorities, as a way of avoiding the need for an isolation transformer but still meeting the ISO directive. However, with two important additions:
1) There must be an easy and obvious way of connecting the on board protective ground wire to the shore side ground wire when the boat is on the hard.
2) It is adviced to use a RCD with a 10 mA threshold instead of the more common 30 mA. This is for increased personal safety reasons.

I fully agree, they are both very sensible additions. Not the 10 mA RCD but somewhere I mentioned a "buried rod when on hard". But maybe I erronously wrote "on dry..."

Daniel

 

[VicS]

I fully agree, they are both very sensible additions. Not the 10 mA RCD but somewhere I mentioned a "buried rod when on hard". But maybe I erronously wrote "on dry..."

Daniel

the trouble with 10mA rcds will probably be that the number of nuisance trips will increase then people will stop using them if they can.

Connecting to earthing rods just ins't going to happen either is it, except in a strictly run yard with an high safety culture ?

 

[PuffTheMagicDragon]

Call me an ignorant Luddite, if you will, but I would only start to consider believing in RCDs when the electrician who fits them is willing to touch the live bits when he is standing in wet feet to demonstrate that they are worth the space.

 

[VicS]

Call me an ignorant Luddite, if you will, but I would only start to consider believing in RCDs when the electrician who fits them is willing to touch the live bits when he is standing in wet feet to demonstrate that they are worth the space.

They make a useful contribution to safety but they should not be relied upon as the primary safety feature .... Until recently Iso 13297 allowed the shorepower earth not to be bonded to the boats Dc systems etc, as is now required, provided an all craft RCD was fitted. This "concession" was anomalous as it was not allowed anywhere else and was criticised for relying on the RCD as the primary ( only?) safety device

 

[Niffler]

Genuine question. What does bonding the AC earth to DC neutral do?

 

[VicS]

Genuine question. What does bonding the AC earth to DC neutral do?

in the very unlikely event of a fault occurring that makes the DC system live the RCD or mcb will trip if the DC system is connected to the AC system protective conductor (earth)

 

[rogerthebodger]

in the very unlikely event of a fault occurring that makes the DC system live the RCD or mcb will trip if the DC system is connected to the AC system protective conductor (earth)

The salient point is :very unlikely event"

IMHO there is only 2 ways this can happen

1) damage to a DC wire and AC wire that causes a short across systems.

As the AC wires and DC wires should be run in separate conduits/trunking this should, in a corrected wired setup, not possible.

2) If you have any equipment that connects to both AC and DC systems and a fault occurs.

The possible normal boat equipment would be mains battery charges or switch mode power supplied like you get in some computers.

Marine battery charges should have step down transformers what would also act as an isolation transformer and the same with computers of better power the computer direct from the DC system.

My boat is setup this way so I have no need to connect my DC system to my hull or the earth of my mains system.

Having a steel hull my mains earth is connected to the hull through a GI and no DC negative to hull connection so no DC to mains earth connection.

My Question to those who say it is important to connect DC negative to mains earth, what danger can occur when there is no connection on a GRP boat and a metal. IMHO the 2 different types of boat construction require different setups.

 

[BabaYaga]

Genuine question. What does bonding the AC earth to DC neutral do?

Assuming you mean the DC negative, I think there is a common misconception that the ISO directive says the AC protective earth should be connected to the DC system per se.
What it says is that the AC protective earth should be connected to "the main grounding/earthing point of the craft". In practice, that may well mean that the AC ground and DC negative are connected, but the purpose of the regulation is clearly to make sure that the AC protective ground wire has a connection to earth/the sea.
This purpose gets even more obvious by the additional regulation that in the case of a fully insulated DC system (no connection to the sea), the AC protective earth should be connected the hull (of a metal boat) or to an external ground plate (for a GRP boat).

 

[VicS]

In practice, that may well mean that the AC ground and DC negative are connected, but the purpose of the regulation is clearly to make sure that the AC protective ground wire has a connection to earth/the sea.

That does not automatically follow. there is nothing specified that connects the main grounding point to the sea in the case of grp vessel. IIRC there is reference to connecting to an external ground plate if one is fitted but there is not actually any requirement to fit a ground plate.

if i were to fit a shorepower system to my boat there would be no connection with the sea even if the shorepower system was installed . Not even, AFAICS, if the installation observed every crossed t and dotted i of iso 13297. No anodes, no metal though hulls no inboard engine, no ground plate

 

[BabaYaga]

That does not automatically follow. there is nothing specified that connects the main grounding point to the sea in the case of grp vessel. IIRC there is reference to connecting to an external ground plate if one is fitted but there is not actually any requirement to fit a ground plate.

if i were to fit a shorepower system to my boat there would be no connection with the sea even if the shorepower system was installed . Not even, AFAICS, if the installation observed every crossed t and dotted i of iso 13297. No anodes, no metal though hulls no inboard engine, no ground plate

The directive frequently uses the term "main grounding/earthing point", I take that to mean grounding and earthing in this context being the same thing (but could be wrong of course).
The directive 13297 makes reference to another directive, ISO 10133, for the definition of "a fully isolated DC system", and then states, for non-conductive hulls, the AC protective ground should be connected to "the craft's external ground/earth or ground plate".
So my guess is that if you were to install shore power in your boat as described, you would have to also install a ground plate (to fully meet the ISO directive).

 

[rogerthebodger]

for the definition of "a fully isolated DC system", and then states, for non-conductive hulls, the DC protective ground should be connected to "the craft's external ground/earth or ground plate".


When statements like this are made I always ask why and what is unsafe if this is not done .

Also does it mean that on a conductive hull, like mine, that the "DC protective ground should NOT be connected to "the craft's external ground/earth or ground plate"

And what is the DC protective ground ?

 

[BabaYaga]

And what is the DC protective ground ?

Sorry, my mistake, should have been AC. Have edited my post.

 

[VicS]

The directive frequently uses the term "main grounding/earthing point", I take that to mean grounding and earthing in this context being the same thing (but could be wrong of course).
The directive 13297 makes reference to another directive, ISO 10133, for the definition of "a fully isolated DC system", and then states, for non-conductive hulls, the AC protective ground should be connected to "the craft's external ground/earth or ground plate".
So my guess is that if you were to install shore power in your boat as described, you would have to also install a ground plate (to fully meet the ISO directive).

No it only requires connection to a ground plate "if fitted". At least thats what it says in the edition of 13297 I have.

My link to the 2012 edition no longer works and I have yet to see a 2014 edition. Is there now a definite requirement in the 2014 edition to fit a ground plate or have they merely omitted the words "if fitted"?

 

[BabaYaga]

No it only requires connection to a ground plate "if fitted". At least thats what it says in the edition of 13297 I have.

My link to the 2012 edition no longer works and I have yet to see a 2014 edition. Is there now a definite requirement in the 2014 edition to fit a ground plate or have they merely omitted the words "if fitted"?

I only have access to the 2012 edition, I cannot find the words "if fitted" in relation to this. The phrasing goes (section 4.2b): "for non-conductive hulls, the craft's external ground/earth or ground plate".

 

[VicS]

I only have access to the 2012 edition, I cannot find the words "if fitted" in relation to this. The phrasing goes (section 4.2b): "for non-conductive hulls, the craft's external ground/earth or ground plate".

But there is no requirement to fit one as far as I can remember. It cn only be connected if it exists.

It will be interesting to see what the 2014 edition says. Logically it will once again say "if fitted" or will spell out the requirement for one to be fitted.

I dont understand yor obsession with connecting the boat's protective conductor and equipotentil bonding to the sea when its already connected to the shorepower earth.


EDIT: Just discovered I have a saved copy of the 2012 edition .... will read that now.

 

[BabaYaga]

But there is no requirement to fit one as far as I can remember. It cn only be connected if it exists.

It will be interesting to see what the 2014 edition says. Logically it will once again say "if fitted" or will spell out the requirement for one to be fitted.

I dont understand yor obsession with connecting the boat's protective conductor and equipotentil bonding to the sea when its already connected to the shorepower earth.


EDIT: Just discovered I have a saved copy of the 2012 edition .... will read that now.

Certainly no obsession of mine, I just find it interesting trying to understand a) what the ISO 13297 actually says on this subject and b) if possible, what purpose there is for the requirements.
So it has nothing to do with my personal opinion och practice. I have neither ground plate nor isolation transformer on my boat, well aware it doesn't meet the directive. Not trying to tell other people what to do, still it can be valuable to know the rules and the reasons for them.
The purpose of what the directive says on this subject, in my interpretation, is that the boats protective AC conductor should be connected to the sea one way or the other (metal hull, engine-shaft-propeller, external ground plate...) so that there is an alternative connection to ground/earth if the shorepower protective earth wire should fail.