Earth Bonding a new Shore Power installation

[aquaholic]

I am at the stage in the project where I will be installing a 240v system on the boat and I realise there has been much said about whether to bond or not, but if I do would it be ok to earth to an anode on the hull which also connected to the engine or should I look to bond somewhere else.

Also am I right in thinking that I should make the earth before the consumer unit or can I earth direct from the unit?

Thanks

 

[lpdsn]

I am at the stage in the project where I will be installing a 240v system on the boat and I realise there has been much said about whether to bond or not, but if I do would it be ok to earth to an anode on the hull which also connected to the engine or should I look to bond somewhere else.

Also am I right in thinking that I should make the earth before the consumer unit or can I earth direct from the unit?

Thanks

The problem with connecting the mains earth directly to the hull is that of galvanic corrossion. Lots of old and not so old threads on here and a few people with good expertise in the subject, so I'll leave them to supply the details. Bottom line is don't do it.

Your 12V system is almost certainly grounded to the engine and maybe elsewhere. Your mains charger should isolate the 12V system from the 230V system. So you could just leave the two separate.

However the problem you might have then is shorting between the 230V wiring and the 12V wiring. Low probability of it happening but potentially fatal consequences if it does.

The standard solution is a Galvanic Isolator. They cost about £100. You use them to break the incoming earth wire so that the earth of the boat is isolated from the earth on the pontoon, preventing galvanic corrosion. They are made up of power diodes which will conduct when the difference reaches about 0.7V, so you still have an earth for safety.

Bear in mind that if you or your dog is thinking of, say, chewing a mains cable, causing a few hundred or few thousand amps to flow down the earth wire, that you must have an RCD to break the connection. Very high current associated with shorts will burn out the diodes in the GI, requiring it to be replaced.

I've chosen to mount my GI between the 230V and 12V systems. This is NOT the standard way of doing things, but I'm happier having the mains earth being continuous and am confident that there is no galvanic corrosion path that does not involve the 12V wiring.

The earth wires probably passes straight through your consumer unit.

 

[VicS]

The shorepower protective conductor ( earth to you and me) should be connected to the DC negative ground ( earth) as close as practical to the battery negative terminal.

You should however make yourself familiar with the latest edition ( 2014 ) of the international standard for AC installations in small craft ISO 13297. There are separate requirements for craft with isolated Dc systems or metal hulls

I only have the 2001 edition which I think can be found on line without difficulty but there have been two editions , 2012 and 2014, since then.

I suggest you beg borrow or steal a copy of the 2014 edition.

 

[Plevier]

There's the 2012 edition at https://law.resource.org/pub/bg/ibr/bds.en.iso.13297.2012.pdf

You can see part of the 2014 at https://www.iso.org/obp/ui/#iso:std:iso:13297:ed-4:v1:en
The only difference in the list of contents is that annex E seems to have disappeared.

 

[BabaYaga]

The shorepower protective conductor ( earth to you and me) should be connected to the DC negative ground ( earth) as close as practical to the battery negative terminal.

You should however make yourself familiar with the latest edition ( 2014 ) of the international standard for AC installations in small craft ISO 13297. There are separate requirements for craft with isolated Dc systems or metal hulls

From what I can see the standard says (point 4.4) that the AC protective conductor should be connected to the boats grounding point.
As I understand it this could be the DC negative or engine block, but only if this has a good connection to earth (the sea).
Connecting the AC protective conductor to a DC system that is isolated from ground (the sea) must surely be pointless?

 

[VicS]

From what I can see the standard says (point 4.4) that the AC protective conductor should be connected to the boats grounding point.
As I understand it this could be the AC negative or engine block, but only if this has a good connection to earth (the sea).
Connecting the AC protective conductor to a DC system that is isolated from ground (the sea) must surely be pointless?

Having now found the 2012 edition on line I am puzzled to some extent because it only seems to consider the situation where the DC system is fully isolated. It does however imply that non metallic hulled craft must have an external ground plate. If a connection exists between a bronze grounding plate and any anodes it is going to have a serious effect in anode life.

The object of connecting the shorepower earth to the Dc system as I understood it was part of achieving equipotential bonding of all exposed metal items.

Maybe the new version of ISO 13297 should be read in conjunction with ISO 10133 ????

I am more than "puzzled to some extent" I am so bewildered I am beginning to lose my appetite for understanding it all. The diagrams in Annexe D dont help

 

[PaulMcC]

From what I can see the standard says (point 4.4) that the AC protective conductor should be connected to the boats grounding point.
As I understand it this could be the AC negative or engine block, but only if this has a good connection to earth (the sea).
Connecting the AC protective conductor to a DC system that is isolated from ground (the sea) must surely be pointless?

Yes but the your DC negative will probably be grounded (although it is possible it isn't) as it is likely that the engine is connected to the DC negative because that's how most marine engines are, and therefore there is a route to ground through the engine and propshaft. There is a decent write up of the pros and cons on Mr Smartguage's webpages.
http://www.smartgauge.co.uk/earthing.html
The recommendations are the same as given by most other authorities (Nigel Calder, various governing bodies, etc) but also fairly easy to follow.

 

[Plevier]

Having now found the 2012 edition on line I am puzzled to some extent because it only seems to consider the situation where the DC system is fully isolated. It does however imply that non metallic hulled craft must have an external ground plate. If a connection exists between a bronze grounding plate and any anodes it is going to have a serious effect in anode life.

The object of connecting the shorepower earth to the Dc system as I understood it was part of achieving equipotential bonding of all exposed metal items.

Maybe the new version of ISO 13297 should be read in conjunction with ISO 10133 ????

I am more than "puzzled to some extent" I am so bewildered I am beginning to lose my appetite for understanding it all. The diagrams in Annexe D dont help

I agree!
I found 10133 on line as well but it didn't help.

 

[ianj99]

The shorepower protective conductor ( earth to you and me) should be connected to the DC negative ground ( earth) as close as practical to the battery negative terminal.

I don't think this applies if you use a transformer for isolation. You connect the onboard earth to an anode but only use the shore earth to earth the transformer and not connect it to the boats mains.

Its the method I have used for 3 years and have no issues, the onboard rcd trips when tested and no probs with galvanic corrosion (my hull is steel and the DC circuits & engine electrics are insulated return)

 

[VicS]

I don't think this applies if you use a transformer for isolation. You connect the onboard earth to an anode but only use the shore earth to earth the transformer and not connect it to the boats mains.

Its the method I have used for 3 years and have no issues, the onboard rcd trips when tested and no probs with galvanic corrosion (my hull is steel and the DC circuits & engine electrics are insulated return)

Yes you are right
Its shown in one of the diagrams in 13297-2012, but not to be confused with a polarisation transformer

 

[ianj99]

Yes you are right
Its shown in one of the diagrams in 13297-2012, but not to be confused with a polarisation transformer

I use the 1600va one from: http://www.airlinktransformers.com/boating_transformers/

They are more costly solution, but possibly safer and more reliable, and probably best for steel or aluminium hulls.

 

[BabaYaga]

Yes but the your DC negative will probably be grounded (although it is possible it isn't) as it is likely that the engine is connected to the DC negative because that's how most marine engines are, and therefore there is a route to ground through the engine and propshaft. There is a decent write up of the pros and cons on Mr Smartguage's webpages.
http://www.smartgauge.co.uk/earthing.html
The recommendations are the same as given by most other authorities (Nigel Calder, various governing bodies, etc) but also fairly easy to follow.

Many boats have a sail drive or, like mine, a flexible coupling between gearbox and prop shaft, isolating the engine from the sea.
I think there is a fairly widespread misconception that the AC ground line is required to be bonded to the DC negative, when in fact the requirement is that it should be bonded to earth (the sea). DC negative might or might not be connected to the sea.
Thanks for the link, though I must say I did not find Mr Smartguage's write up totally convincing.
PS I've edited my post: DC negative.