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Advice sought re. battery replacement


Froggy

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Here's a point that interests me though: if you look at the wiring instructions for the Victron in the .pdf document linked earlier, it makes clear that three-core cable should be used and shows a diagram with the earth wire connecting to a terminal. So, where does that earth cable go to on a boat?.....

EDIT: I'll answer that myself. On page 23 it states:

Connect the mains earth wire
to the earth terminal of the
AC terminal block. An M4
earth screw is fitted in the bot-
tom of the cabinet. Connect
the cabinet earth to the ves-
sel’s hull or earth plate and in
the case of motor vehicles to
the chassis.
 
Edited by Froggy
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1 hour ago, Froggy said:

Just to avoid confusion though, our boat has RCDs, the issue is that a short in the mains circuit when powered by the inverter doesn't seem to trigger them.

That's because when Victron designed that unit boats weren't fitted with RCDs, so the unit doesn't do the automatic N-E bonding when in Inverter mode. Their more modern units do. 

As I said before, contact Victron and ask if they offer that feature as a retro-fit. 

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48 minutes ago, WotEver said:

That's because when Victron designed that unit boats weren't fitted with RCDs, so the unit doesn't do the automatic N-E bonding when in Inverter mode. Their more modern units do. 

As I said before, contact Victron and ask if they offer that feature as a retro-fit. 

See the post above yours. :)

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2 minutes ago, WotEver said:

Yup saw that after I'd posted. 

In the post above that one i note that the earth is meant to connect to the hull (or an earth plate). What are your opinions on that? Surely this adds some protection? It can presumably potentially make the whole hull live but I'm guessing that then the earlier discussed short circuit protection kicks in and/or the Victron cant cope with the load so the overload protection kicks in, either way shutting the system off.

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1 hour ago, Froggy said:

In the post above that one i note that the earth is meant to connect to the hull (or an earth plate). What are your opinions on that? Surely this adds some protection? It can presumably potentially make the whole hull live but I'm guessing that then the earlier discussed short circuit protection kicks in and/or the Victron cant cope with the load so the overload protection kicks in, either way shutting the system off.

Yes, the case should be earthed to the main AC earth stud (which should be adjacent to the main DC -ve stud, probably somewhere close to the batteries). 

Without the N-E bond the inverter supply is no different to tens of thousands of houses which have no RCD fitted. It's not even mandatory to have an RCD for the BSS, simply 'Strongly Advised'. However, as you have one it would be nice to have it functioning correctly. 

Edited by WotEver
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9 minutes ago, WotEver said:

Yes, the case should be earthed to the main AC earth stud (which should be adjacent to the main DC -ve stud, probably somewhere close to the batteries). 

Without the N-E bond the inverter supply is no different to tens of thousands of houses which have no RCD fitted. It's not even mandatory to have an RCD for the BSS, simply 'Strongly Advised'. However, as you have one it would be nice to have it functioning correctly. 

I'm certainly no electrician, but I'm guessing that if you hooked up a live wire to a boat hull from 240v mains it would just keep pumping current through (without the RCD protection that exists at marina hookups) and quite easily fry you, but I suspect that a small inverter couldn't cope with anything like such a load and so would simply shut down (as per overload protection cited in the .pdf document).

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2 minutes ago, Froggy said:

I'm certainly no electrician, but I'm guessing that if you hooked up a live wire to a boat hull from 240v mains it would just keep pumping current through (without the RCD protection that exists at marina hookups) and quite easily fry you, but I suspect that a small inverter couldn't cope with anything like such a load and so would simply shut down (as per overload protection cited in the .pdf document).

No, that's not correct. 

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5 minutes ago, WotEver said:

No, that's not correct. 

Why? How much current can be drawn from a small bank of batteries and then dissipated through the entire hull? If this isn't the case what protection does earthing to the hull provide?

Edited by Froggy
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The above scenario is I believe an unlikely one anyway because I suspect that the boat fitters went to great lengths to ensure that all 240v cables were well insulated from the hull. This leaves the main danger that you could touch a live wire on a poorly fitted appliance, and perhaps fitting rcd protection on the sockets is the best that can be done to protect against this.

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The OP has a naive and shallow understanding of boat electrics across the board. This is not a blameworthy fault, it is just a consequence of taking on a big challenge without experience. I would strongly recommend him to attend TB's (now RCR's) excellent training courses before making any more purchases or decisions, to the extent that that is possible. It is just not possible to fill so many holes via a discussion forum. Each answer generates a response that needs a further explanation. IMHO.

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2 hours ago, Froggy said:

Why? How much current can be drawn from a small bank of batteries and then dissipated through the entire hull? If this isn't the case what protection does earthing to the hull provide?

Have a read of this and see if it helps...

http://smartgauge.co.uk/earthing.html

28 minutes ago, system 4-50 said:

Each answer generates a response that needs a further explanation. IMHO.

Agreed, hence I'm now trying to just point to online resources where someone else has done all the typing.  Like Gibbo ;)

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1 hour ago, system 4-50 said:

The OP has a naive and shallow understanding of boat electrics across the board. This is not a blameworthy fault, it is just a consequence of taking on a big challenge without experience. I would strongly recommend him to attend TB's (now RCR's) excellent training courses before making any more purchases or decisions, to the extent that that is possible. It is just not possible to fill so many holes via a discussion forum. Each answer generates a response that needs a further explanation. IMHO.

 

45 minutes ago, WotEver said:

Have a read of this and see if it helps...

http://smartgauge.co.uk/earthing.html

Agreed, hence I'm now trying to just point to online resources where someone else has done all the typing.  Like Gibbo ;)

Ok, I might be naive regarding boat electrics, as I pointed out a few posts ago, but I'm not stupid, and in fact this qoute from the article WotEver has linked to backs up what I was saying myself:

"Had the AC system had it's earth conductor bonded to the hull this situation could not arise because as soon as the live cable touched the hull either the fuse would blow or the inverter or generator would cut-out having detected an overload."

This deduction was arrived at by a bit of logic and lateral thinking in lieu of expert knowledge on the subject :) Expert opinion is, of course, divided, as the article acknowledges.

Thanks anyway for the useful link, which I will keep for reference.

Edited by Froggy
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But you must also understand that this is an entirely different subject to the operation of an RCD. An RCD will cut the power the instant a human 'begins' to get a shock. It has nothing to do with the live wire shorting to the hull and everything to do with the protection of life should a person touch a live wire. 

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2 minutes ago, WotEver said:

But you must also understand that this is an entirely different subject to the operation of an RCD. An RCD will cut the power the instant a human 'begins' to get a shock. It has nothing to do with the live wire shorting to the hull and everything to do with the protection of life should a person touch a live wire. 

This highlights the problem.

Having 'little or no knowledge' on the subject, the questioner does not understand the answer and gets confused thinking that the question has been answered, whilst actually the answer has been misunderstood and led the questioner to believe that something he (mis)read actually answered the question (whilst not appreciating/knowing what the function of an RCD is).

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3 hours ago, WotEver said:

But you must also understand that this is an entirely different subject to the operation of an RCD. An RCD will cut the power the instant a human 'begins' to get a shock. It has nothing to do with the live wire shorting to the hull and everything to do with the protection of life should a person touch a live wire. 

 

3 hours ago, Alan de Enfield said:

This highlights the problem.

Having 'little or no knowledge' on the subject, the questioner does not understand the answer and gets confused thinking that the question has been answered, whilst actually the answer has been misunderstood and led the questioner to believe that something he (mis)read actually answered the question (whilst not appreciating/knowing what the function of an RCD is).

 

But my main concern is that there is protection, whatever means it is provided by. The discussion began as specific to RCDs but then extended to the general danger of an electric shock in a boat from an unprotected 240v current via an inverter. At one point earlier today i queried what would happen if a live wire shorted against the hull. The inverter shutting down due to detecting overload in such an eventuality is imo pretty acceptable protection. I have acknowledged 7 posts up that there is still a danger from poorly fitted (or maintained) appliances where a person comes into direct contact with a live wire. This, as the linked article infers, can largely be avoided by purchasing good quality equipment that is double insulated, and then ensuring that this equipment is properly fused and properly maintained. The RCD clearly offers more effective protection but at least the protection isn't non-existent and, in the case of a live wire shorting to the hull (which is a hidden danger that can't readily be pre-empted) is probably more than adequate. I appreciate the help that has been offered in this thread, particularly the effort that WotEver has gone to (in stark contrast to the derision proffered by Northernboater). I don't profess to have much knowledge on the subject, hence the reason why i posted in the New To Boating section!

It's unlikely that we'll be forking out to replace the inverter because of this shortcoming, so will have to make do with what we have. I'm sure there are a vast number of others out there in the same boat, figuratively speaking. I will feed back any reply i get from Victron, and might also contact the original fitters, JD Narrowboats.

Edited by Froggy
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Let me share this with you as it may help others that have been following this thread.

In a place with a supply from the 'mains' - say a house - the capability of the supply is massive, in the order of hundreds of amps, if not thousands of amps.  Your installation is maybe designed for a maximum of 100A, with individual sockets being 13amps, so cables, connectors etc are all sized for that level.  However in the event of a fault to prevent things like cables etc being grossly overloaded and catching fire a fuse or circuit breaker will be fitted.  This will break the circuit before serious damage/fire.  Now with a small generator, or solar panel or inverter the output is very limited and the fault current will be little more than the max rating of the equipment, so it is not surprising that the inverter shuts down to protect itself before the fuse blows or breaker trips out.  Therefore a short between the live and hull may shut down the inverter much faster than a fuse or breaker will trip.  So a fuse/breaker is basically there to protect the installation against fire etc and not really to protect people.

People only need a few milliamps (just a few watts) to be harmed / killed.  So a different technology is required.  This is a small device that monitors the current flowing along the live wire and compares it to the current flowing along the neutral wire.  If they are the same no current is leaking out to earth, but if they are more than typically 30mA different the circuit will see this as a fault and trip out.  However this does require the current to be able to flow through the fault (maybe you holding a faulty appliance) into the earth/hull of your boat along the earth and back into the supply - your inverter or generator etc.  This requires the neutral and earth wires to be bonded together at the supply source.

In the past it was felt acceptable to have the supply completely isolated from the earth, so in the event of a fault, current would not flow to earth through you.  This is no longer accepted for new builds as an acceptable practice because it does have some risks and an RCD is sufficiently low cost and reliable so there is no justification to not design one into a new system.

As to updating your system, some older inverters were designed such that it was acceptable to bond the neutral and earth together, but in others it is not possible.  Also you must not directly bond the earth and neutral together for the shore supply, that is forbidden, so the wiring changes to 'update' an existing installation could be complex and must be left to those that understand your system.

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3 hours ago, Chewbacka said:

Let me share this with you as it may help others that have been following this thread.

In a place with a supply from the 'mains' - say a house - the capability of the supply is massive, in the order of hundreds of amps, if not thousands of amps.  Your installation is maybe designed for a maximum of 100A, with individual sockets being 13amps, so cables, connectors etc are all sized for that level.  However in the event of a fault to prevent things like cables etc being grossly overloaded and catching fire a fuse or circuit breaker will be fitted.  This will break the circuit before serious damage/fire.  Now with a small generator, or solar panel or inverter the output is very limited and the fault current will be little more than the max rating of the equipment, so it is not surprising that the inverter shuts down to protect itself before the fuse blows or breaker trips out.  Therefore a short between the live and hull may shut down the inverter much faster than a fuse or breaker will trip.  So a fuse/breaker is basically there to protect the installation against fire etc and not really to protect people.

People only need a few milliamps (just a few watts) to be harmed / killed.  So a different technology is required.  This is a small device that monitors the current flowing along the live wire and compares it to the current flowing along the neutral wire.  If they are the same no current is leaking out to earth, but if they are more than typically 30mA different the circuit will see this as a fault and trip out.  However this does require the current to be able to flow through the fault (maybe you holding a faulty appliance) into the earth/hull of your boat along the earth and back into the supply - your inverter or generator etc.  This requires the neutral and earth wires to be bonded together at the supply source.

In the past it was felt acceptable to have the supply completely isolated from the earth, so in the event of a fault, current would not flow to earth through you.  This is no longer accepted for new builds as an acceptable practice because it does have some risks and an RCD is sufficiently low cost and reliable so there is no justification to not design one into a new system.

As to updating your system, some older inverters were designed such that it was acceptable to bond the neutral and earth together, but in others it is not possible.  Also you must not directly bond the earth and neutral together for the shore supply, that is forbidden, so the wiring changes to 'update' an existing installation could be complex and must be left to those that understand your system.

Many thanks for your helpful answer. Your comments seem to confirm my deduction (from other advice offered in the thread) that our boat is probably adequately safeguarded from a short to the hull (which is probably unlikely if the boat fitters did their job properly) but that users are at some risk from shorts within individual appliances when powered through the inverter. I'm not at the boat at present and although we should have a spare copy of the manual at home i can't find it (i think i took it to the boat to compare with the other one because some pages seem to be missing from one copy). I can remember the manual stating that the hull isn't used as a return but am not too sure about the earth arrangement; however i suspect from what i can remember of the circuit diagrams that the earth is bonded to the hull.

As i was typing the above a very pleasant lady from Victron telephoned me all the way from Holland! She went into some detail to explain the inverter, including stating that it wasn't a sine wave model and therefore sensitive equipment like laptops might be prone to damage. She was of course in part trying to sell me a new model, and i was surprised to discover that a replacement would cost less than £900 because for some reason i thought they were several grand. It's possibly something that we might therefore consider later in the year or more likely next year. She confirmed that the earth-neutral bonding is done by means of a relay and can't be retro-fittedd to older models, but also said that the Victron is 'floating' and not earthed to the rest of the system (something i don't fully understand) and that she has never heard of anybody receiving an electric shock from these systems in the past.

I'm going to have a long punt now and contact the original boat builder, JD Narrowboats, and see if they can shed any further light on things.

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Does anybody know how to retrospectively add tags to this thread because it might be a good idea to add a tag for 'inverter' given how the discussion has wandered away from my original query about batteries?

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17 minutes ago, Froggy said:

the Victron is 'floating' and not earthed to the rest of the system (something i don't fully understand) and that she has never heard of anybody receiving an electric shock from these systems in the past.

It means that the two output mains wires (nominally Live and Neutral) have no reference to earth. In other words if you were to grab hold of the 'live' wire with one hand and the hull with the other you would receive no shock. Likewise if you did the same with the 'neutral' wire and hull. The only way you could receive a 230V shock would be to grab hold of both 'live' and 'neutral' at the same time. 

So yes, it's as safe as can be :)

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2 minutes ago, WotEver said:

It means that the two output mains wires (nominally Live and Neutral) have no reference to earth. In other words if you were to grab hold of the 'live' wire with one hand and the hull with the other you would receive no shock. Likewise if you did the same with the 'neutral' wire and hull. The only way you could receive a 230V shock would be to grab hold of both 'live' and 'neutral' at the same time. 

So yes, it's as safe as can be :)

Agreed, but could change depending upon what is plugged into your sockets.  For example some old SMPS will have capacitors between phase and earth and between neutral and earth to help soak up hf noise, so there is possibly a 'weak' reference to earth, so you might experience a bit of a shock if you touch things.   As they say on kids TV don't try this at home.

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11 minutes ago, WotEver said:

It means that the two output mains wires (nominally Live and Neutral) have no reference to earth. In other words if you were to grab hold of the 'live' wire with one hand and the hull with the other you would receive no shock. Likewise if you did the same with the 'neutral' wire and hull. The only way you could receive a 230V shock would be to grab hold of both 'live' and 'neutral' at the same time. 

So yes, it's as safe as can be :)

 

2 minutes ago, Chewbacka said:

Agreed, but could change depending upon what is plugged into your sockets.  For example some old SMPS will have capacitors between phase and earth and between neutral and earth to help soak up hf noise, so there is possibly a 'weak' reference to earth, so you might experience a bit of a shock if you touch things.   As they say on kids TV don't try this at home.

Now i'm outside the realm of my knowledge again though because doesn't that .pdf Victron manual linked above make reference to earthing the unit? If having the live and neutral isolated from earth worked why did later designs move towards bonding the earth and neutral? Presumably because the RCD route was even safer?

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Yes the RCD route is considered safer than a floating supply.  As briefly discussed above a floating supply is very safe but might with certain unusual appliance fault conditions be less safe than you would like.  As the people that write the regs have no control as to what you will plug into your system, they tend to specify considering 'worst case'.  As RCD's are now affordable and reliable the regs require them for new builds.  It's all about risk management.  As the nice lady from Victron told you, in the real world she has not heard of anyone being harmed by a floating system.  It is also a balance between cost, reliability and risk.  So a few years back the regs required a 10mA RCD in certain high risk locations on a boat, but I think that has now been dropped and 30mA is ok.  -  10mA will suffer from nuisance trips etc. far more so than 30mA.

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