Earthing 'mains' circuit on my boat

[PaulRainbow]

There is an important recent change in regard to marina swimming inasmuch as SUP users are now often also boatowners and as such use their boats in their marina berths as very convenient launch points. Falling in (a lot !) is part of the learning curve. And many river based marinas will have water bordering on fresh especially after heavy rainfall.

This is one of the reasons I routinely fish immersed shorepower cables out of the water if I see them, as well as to reduce stray higher voltage AC current corrosion, which ignores the niceties of a GI, and can destroy underwater metalwork in short order.

Those are all good points Trevor.

I'm with you on fishing shore power cables out of the water

 

[superheat6k]

Those are all good points Trevor.

I'm with you on fishing shore power cables out of the water

I do wonder if a duty of care exists burden upon marina operators in regard to ensuring as far as they reasonably can to ensure vessels using their facilities have safe shorepower grounding systems. None, as far as I know, ask any questions about and certainly do not ever check individual boat's earth bonding systems, and sadly far too many owners' attitudes are either of complete ignorance or that anode bonding to the shore PE causes other issues, and whereas this can be the case, only because other defects also exist within an installation.

I abhor the idea of a BSS scheme for sea navigable boats, but I do see this as one area that could see such a scheme becoming mandatory, especially if we do start seeing deaths due to electric shock drowning. This could easily happen on the Hamble now, which this year with the World and his Wife unable to do very much else at all, and that even The Range are now flogging SUPs will make the rare possibility of an electric shock drowning frighteningly more likely, as well as making navigating the River a nightmare this coming season. I'm expecting swarms of the bloody things (including the one we own - but we do at least know the River's rules !).

 

[johnalison]

I found #10 very interesting, though, to be honest, I don’t think that I grasped it all. In spite of having A-level physics granted to me by Alfred the Great, such phrases as ‘the neural and earth must be bonded at source’ don’t fully convey what is required. I think that I need to reread in in the cool light of the morning, but my boat was built to the standards of twenty years ago and I live in hope that this will suffice.

 

[PaulRainbow]

I found #10 very interesting, though, to be honest, I don’t think that I grasped it all. In spite of having A-level physics granted to me by Alfred the Great, such phrases as ‘the neural and earth must be bonded at source’ don’t fully convey what is required. I think that I need to reread in in the cool light of the morning, but my boat was built to the standards of twenty years ago and I live in hope that this will suffice.

"Bonded" simply means "joined" or "connected" John. So if you were fitting, say, an inverter, it means you must join the neutral and Earth together at the inverter, in the same way that the shore power is dome shoreside.

If you only have shore power on your boat, no need to worry about bonding, that's done shoreside. At 20 years old the shore power Earth is unlikely to be connected to "the water". As i said in post #10, "There are no regulatory requirements that force retrofitting to boats built prior to it becoming a requirement".

Boat owners who use their boats in fresh water, where swimmers might be around, and would be connected to shore power ought to consider making the change though, IMO.

 

[superheat6k]

I found #10 very interesting, though, to be honest, I don’t think that I grasped it all. In spite of having A-level physics granted to me by Alfred the Great, such phrases as ‘the neural and earth must be bonded at source’ don’t fully convey what is required. I think that I need to reread in in the cool light of the morning, but my boat was built to the standards of twenty years ago and I live in hope that this will suffice.

In essence the Earth wire and the Neutral wire in any installation are always connected, but the key difference is that the Earth (or PE 'Protective Earth') does not carry current in normal circumstances. It only conducts if a fault occurs somewhere within the system (e.g. a short arises in a piece of equipment, and because it is 'earthed' the potential (voltage) in the earth conductor is held at earth potential or nil volts, but this is subject to the current handling capability of the PE conductor system at least matching that of the conductor with the fault on .

It is important the Earth and Neutral ONLY connect at the power source, which for the purposes of a marina shore supply is somewhere upstream of where you plug in. Any other connection between Earth and Neutral can become potentially dangerous because this can cause the normally non conducting earth wire to become an active conductor between the true and false neutral.

In regard to other power sources such as Generators and Inverters the earthing of the neutral at source (i.e. right where the cables emerge from the item and inside its casings) requirement still exists, and for the reason of not having two earth to neutral connections on the same system (as well as issues of paralleling beyond the scope of this thread) it is vital the controlling switch for the various supplies must never allow the neutrals (as well as lives) from any two sources to be connected at the same time, so load break switches must be double pole and 'break before make' between various sources. This is why On - Off - On switches are ideal, and where there are three sources of supply (Shore / Generator / Inverter) a five position switch providing On - Off - On - Off - On is in my view preferable.

This is also why when it comes to dealing with 240vac on boats if you are not sure then the only way to be sure you won't end up dead is to pay a man who is sure.

 

[PaulRainbow]

I do wonder if a duty of care exists burden upon marina operators in regard to ensuring as far as they reasonably can to ensure vessels using their facilities have safe shorepower grounding systems. None, as far as I know, ask any questions about and certainly do not ever check individual boat's earth bonding systems, and sadly far too many owners' attitudes are either of complete ignorance or that anode bonding to the shore PE causes other issues, and whereas this can be the case, only because other defects also exist within an installation.

I abhor the idea of a BSS scheme for sea navigable boats, but I do see this as one area that could see such a scheme becoming mandatory, especially if we do start seeing deaths due to electric shock drowning. This could easily happen on the Hamble now, which this year with the World and his Wife unable to do very much else at all, and that even The Range are now flogging SUPs will make the rare possibility of an electric shock drowning frighteningly more likely, as well as making navigating the River a nightmare this coming season. I'm expecting swarms of the bloody things (including the one we own - but we do at least know the River's rules !).

It might be worth remembering that it's not so important in sea water, as i understand it, but it certainly bears some though for those who boat in fresh water.

I'm also not keen at all on a BSS type scheme, but i am concerned about the 240v systems on a boat. The cheap Chinese inverters and lack of knowledge of DIY installers is a disaster waiting to happen. I have no doubt that we'll be reading about someone dying or being seriously harmed by such installations anything soon.

I see some shocking 240v wiring on an all too regular basis, this picture is from a fairly modern mobo, circa £200K in value that my client had just purchased. The client wanted to be sure that everything was 100% correct, so in addition to fitting a new nav suite, my remit was to check everything and fix anything that was less than 100% correct, a very sensible man. There was a double socket, spurred of off the fridge ! Someone had added two more sockets, all spurred off of a galley socket, using a mix of any old cable they had lying around.

You can see why i jump up and down a bit in some of the AC/Inverter threads when people start arguing that the Earths don't need connecting

 

[pandos]

Interesting thread...

When discounting the presence f swimmers around marinas...let's not forget those chaps who scrub their boats prior to racing on a Sunday morning...

 

[Daydream believer]

Your van sits on rubber tyres so you can't (as you said) connect anything to Earth.

Some CARAvans sit on jacks, which are connected to the chassis & the ground ( provided the owner does not use plastic pad, of course)

 

[dankilb]

Very informative all, thanks. As both a SUP instructor and an occasional bottom scrubber, I ought to get this one right! ?

Practically speaking - what is the best method of bonding the PE to the boat/water on a 'standard AWB'? I'm more and more convinced now this isn't done on ours, but will confirm when I can get back to the boat...

We only have shaft/prop anodes. Otherwise, all composite through hulls and no other means of grounding I can think of. So am I therefore aiming to connect the PE to the engine's ground somehow? (not necessarily directly, but say via an unswitched -ve bus?)

 

[RupertW]

Very informative all, thanks. As both a SUP instructor and an occasional bottom scrubber, I ought to get this one right! ?

Practically speaking - what is the best method of bonding the PE to the boat/water on a 'standard AWB'? I'm more and more convinced now this isn't done on ours, but will confirm when I can get back to the boat...

We only have shaft/prop anodes. Otherwise, all composite through hulls and no other means of grounding I can think of. So am I therefore aiming to connect the PE to the engine's ground somehow? (not necessarily directly, but say via an unswitched -ve bus?)

I take everything AC and DC (not many connections as I have a negative bus) to an Earth fitting on the engine block. I don’t Earth by individual seacocks.

Altbough the way I have wired mains AC, inverter and the DC systems works well, there are a couple of Paul Rainbow’s observations on this thread that make me wince about a couple of my own choices so need to have more of a think. In particular the negative connotations of spurring (why?) and how my setup which is designed to allow simultaneous AC mains connected and use of the invertor (not for the same mains devices) should be earthed and neutral bonded.

 

[pyrojames]

(My highlighting)

That was what I understood from reading Nigel Calder (yes I know). I was initially worried about not having the earth bonding, but my take now is that it is less important in UK than say US or Southern Europe. It is not normal to swim in marinas in Britain! I cannot think of normal circumstances where I would be plugged in at a marina and anyone would be in the water. Of course to cover all circumstances then the bonding would be safest, but is not on my urgent to-do list especially as I am on a river mooring.

There are often pro divers cleaning boats at Cowes during regattas, and doing underwater work elsewhere.

 

[PaulRainbow]

I take everything AC and DC (not many connections as I have a negative bus) to an Earth fitting on the engine block. I don’t Earth by individual seacocks.

Altbough the way I have wired mains AC, inverter and the DC systems works well, there are a couple of Paul Rainbow’s observations on this thread that make me wince about a couple of my own choices so need to have more of a think. In particular the negative connotations of spurring (why?) and whether my setup which is designed to allow simultaneous AC mains connected and use of the invertor (not for the same mains devices) is earthed and neutral bonded.

Most moderate sized boats are on radial circuits, not the ring mains we have in our houses. So you have, say, a 16a MCB and you run a cable to a socket, then to another socket, then another etc. Unlike a ring main, the last socket doesn't go back to the consumer unit. If you've used cable rated for at least 16a you can't overload the circuit, as the MCB will trip.

Typically, we'd have more than one cable coming from the consumer unit, perhaps one running to the port sockets and one to the starboard sockets, on the same 16a MCB. Possibly a separate socket for the microwave, on its own MCB, etc.

A spur would be a connection from one of the midpoint sockets to a new socket, or chain of sockets. That's a new radial circuit and is bad practice, it would need to be fused where it connects to the original radial. Something i'd avoid. As with domestic ring mains, it is permissible to have one spur on a radial.

 

[PaulRainbow]

Very informative all, thanks. As both a SUP instructor and an occasional bottom scrubber, I ought to get this one right! ?

Practically speaking - what is the best method of bonding the PE to the boat/water on a 'standard AWB'? I'm more and more convinced now this isn't done on ours, but will confirm when I can get back to the boat...

We only have shaft/prop anodes. Otherwise, all composite through hulls and no other means of grounding I can think of. So am I therefore aiming to connect the PE to the engine's ground somehow? (not necessarily directly, but say via an unswitched -ve bus?)

If there is electrical continuity between the shaft and the engine block, it would be ok to connect to the block. If there is no continuity, don't make a connection and don't try and bridge the block/shaft. If there is nothing metal, in contact with the water, that you can connect to, you'd have to add something like a grounding plate or an anode.

 

[RupertW]

Most moderate sized boats are on radial circuits, not the ring mains we have in our houses. So you have, say, a 16a MCB and you run a cable to a socket, then to another socket, then another etc. Unlike a ring main, the last socket doesn't go back to the consumer unit. If you've used cable rated for at least 16a you can't overload the circuit, as the MCB will trip.

Typically, we'd have more than one cable coming from the consumer unit, perhaps one running to the port sockets and one to the starboard sockets, on the same 16a MCB. Possibly a separate socket for the microwave, on its own MCB, etc.

A spur would be a connection from one of the midpoint sockets to a new socket, or chain of sockets. That's a new radial circuit and is bad practice, it would need to be fused where it connects to the original radial. Something i'd avoid. As with domestic ring mains, it is permissible to have one spur on a radial.

Great, thanks - I think I would describe my set up as radial then but I think that there is one spur (for a 2kw water heater - bad me) which I could easily lead a second cable from the MCB and fuse that or maybe simpler to add a double pole MCB so I can leave the original one to break at 16amp total.

 

[PaulRainbow]

Great, thanks - I think I would describe my set up as radial then but I think that there is one spur (for a 2kw water heater - bad me) which I could easily lead a second cable from the MCB and fuse that or maybe simpler to add a double pole MCB so I can leave the original one to break at 16amp total.

One spur is acceptable, but it's "normal" to have the water heater on its own MCB.

If you ran a second cable from the MCB it would not need to be fused, the MCB will still protect it and the original one.

A 16a double pole MCB offers no more current protection than a 16a double pole MCB, it just breaks the live and neutral, rather than just the live.

So, your single spur is OK as long as the MCB is rated for the cable. You're probably on a 16a shore power connection, with a 16a MCB for the radial and hopefully 2.5mm flex for the radial, which would be OK.

If i was to make any changes, i'd run the water heater to its own circuit breaker. On a fairly basic setup i'd fit a socket circuit on its own MCB, the water heater on its own MCB and the battery charger on its own MCB. It can be useful, if the battery charger acts up, to not lose all of the sockets, for instance.

 

[dankilb]

I take everything AC and DC (not many connections as I have a negative bus) to an Earth fitting on the engine block. I don’t Earth by individual seacocks.

If there is electrical continuity between the shaft and the engine block, it would be ok to connect to the block. If there is no continuity, don't make a connection and don't try and bridge the block/shaft. If there is nothing metal, in contact with the water, that you can connect to, you'd have to add something like a grounding plate or an anode.

Many thanks, both. Yes that would work for us - good continuity between shaft/block/DC -VE currently. Good to know the earth bonding can be achieved simply that way...

On the heater spur issue, our current (previous owner’s) installation is definitely one for the hall of shame! The heater is on a fused spur connected directly to the incoming mains plug! The battery charger was wired the same, but just with a plug socket to connected it (before the consumer unit)! Needless to say I’ve ‘condemned’ it all.

A nice feature of the Screwfix garage consumer unit many seem to be a fan of (and I plan to fit too) is it’s got enough spare MCBs for sockets, charger and immersion (if you use the blanked off slot) all separately. So that’s what I plan to do to put it right, together with a shiny new Marinco 32amp plug! ??

 

[RupertW]

One spur is acceptable, but it's "normal" to have the water heater on its own MCB.

If you ran a second cable from the MCB it would not need to be fused, the MCB will still protect it and the original one.

A 16a double pole MCB offers no more current protection than a 16a double pole MCB, it just breaks the live and neutral, rather than just the live.

So, your single spur is OK as long as the MCB is rated for the cable. You're probably on a 16a shore power connection, with a 16a MCB for the radial and hopefully 2.5mm flex for the radial, which would be OK.

If i was to make any changes, i'd run the water heater to its own circuit breaker. On a fairly basic setup i'd fit a socket circuit on its own MCB, the water heater on its own MCB and the battery charger on its own MCB. It can be useful, if the battery charger acts up, to not lose all of the sockets, for instance.

Thanks, really helpful. Yes it’s all 2.5mm. The water heater has its own breaker in the form of a DPDT middle-off switch so that I can change its input between mains and a dedicated inverter/transformer/VSR setup, so you are right I gain no advantage from adding the double MCB so save a few quid.

Edit - and I fitted is a domestic style pre-labelled “Water heater” on/off switch too, years before the DPDT changeover switch.

 

[BabaYaga]

Since the question of 'electric shock drowning' is touched upon in so many of the posts to this thread, perhaps it is worth pointing out that it is the presence of a well functioning RCD in the 'consumer unit' that actually protects the swimmer.

 

[PaulRainbow]

Many thanks, both. Yes that would work for us - good continuity between shaft/block/DC -VE currently. Good to know the earth bonding can be achieved simply that way...

On the heater spur issue, our current (previous owner’s) installation is definitely one for the hall of shame! The heater is on a fused spur connected directly to the incoming mains plug! The battery charger was wired the same, but just with a plug socket to connected it (before the consumer unit)! Needless to say I’ve ‘condemned’ it all.

A nice feature of the Screwfix garage consumer unit many seem to be a fan of (and I plan to fit too) is it’s got enough spare MCBs for sockets, charger and immersion (if you use the blanked off slot) all separately. So that’s what I plan to do to put it right, together with a shiny new Marinco 32amp plug! ??

All sounds a good plan Dan, except the Marinco bit. I'd suggest a Ratio plug/socket. The Marinco sockets have poor contact area. The polished stainless one looks the business and it's waterproof: Hermes Delivery Postcodes sample page | Guernsey Post Ltd

Boat fires:

 

[PaulRainbow]

Thanks, really helpful. Yes it’s all 2.5mm. The water heater has its own breaker in the form of a DPDT middle-off switch so that I can change its input between mains and a dedicated inverter/transformer/VSR setup, so you are right I gain no advantage from adding the double MCB so save a few quid.

Edit - and I fitted is a domestic style pre-labelled “Water heater” on/off switch too, years before the DPDT changeover switch.

That's all fine for the shore power side of things. Just make sure you have some form of protection on the inverter side. If you're just plugged into a "portable installation", note the points in post #10