Piers
Well-known member
So all this makes me wonder why our Fleming 55 has no switch. She's fitted with isolation transformers (fore and aft shore supplies) but no switch. Ought I to find an electrician to fit said 'switch'?
Live metal work when out of the water?
- Thread starter Piers
- Start date
David2452
Active member
Some have an internal "bridge cable" that must be installed before connecting shore power when ashore rather than a switch . what I.T. do you have?
David2452
Active member
Ashore or afloat, a simple cheap mains test device attached to a 16 or 32a plug is all you need and should really be used every time you connect to any unknown supply, not just for PE present but other faults like reversed polarity, if you don't feel comfortable making your own or having one made up then Martindale do one suitable, but it is less versatile as the tester can't be removed to use on 13a sockets. http://martindale-electric.co.uk/martindale-cp201-250v-industrial-socket-tester-p-278.html?osCsid=48678908e8e6328475921be678017a71
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Piers
Well-known member
I.T? No idea. Both are well hidden behind fitted joinery, but I'll see what I find out. There's no info from any of the Fleming data originally passed to me.
Piers
Well-known member
Hi jfm. Just had an email from Fleming stating there's no need for this on their boats! Yes, they fit isolation transformers as standard, but their MD is quite clear that nothing should be done earthing-wise for a Fleming out of the water and still connected to shore power.
Seems strange to me but since he's said it, I at least have a finger point capability if something untoward happened.
David2452
Active member
I would be far more inclined to follow the advice of the IT manufacturer (or manufacturer of any kit come to that) than any builder even of the reputation of Flemming, as I asked earlier, what Isolation Transformer do you have? It's no good pointing a smouldering charred finger at anybody.
Piers
Well-known member
Hi David2352. I attempted to remove one of the substantial coverings to the ITs before taking Play d'eau to the UK for repairs (http://www.playdeau.com/play-deau-and-south-africa/) but time ran out. In addition, I read a report in one of the Fleming mags (Venturer) in which the writer was saying that shore power earthing depended upon whether the IT had been wired for polarisation or isolation, and the checking how it was wired was paramount. That's when I wrote to Fleming asking the qn and pointing out that Fairline appeared to be adding an 'earthing' switch for when out of the water.
That's when I was told there was no such problem associated with our Fleming. The thick plottens as they say. But when we have Play d'eau back I'll ensure the manufacturer is found.
jfm
Well-known member
I totally don't buy that Piers. If someone wants to email me telling me that Thursday isn't the day after Wednesday then that's perfectly ok, but they need to give some explanation. They cant just make the naked statement. (I don't care that he is the manager of Flemming or whatever). I realise that just the RCDs provide much protection on their own, but they don't generally eliminate need for earthing. I'm with David as regarding pointing of charred fingers
Piers
Well-known member
I totally don't buy that Piers. If someone wants to email me telling me that Thursday isn't the day after Wednesday then that's perfectly ok, but they need to give some explanation. They cant just make the naked statement. (I don't care that he is the manager of Flemming or whatever). I realise that just the RCDs provide much protection on their own, but they don't generally eliminate need for earthing. I'm with David as regarding pointing of charred fingers
I agree. BTW, Duncan owns Fleming now. Tony sold it to Duncan and Adi, his nephew(?). I'll keep pressing.
kashurst
Well-known member
to find out how your transformer is operating - measure the resistance from the shore power connector earth to the earth on one of Play d'eau's 240v sockets. (obviously no shore power connected and gennies off) If its open circuit you are not earthed ashore, if it is earthed you are not galvanically isolated. Unless Flemming have fitted a clever switch that knows when the boat is in the water.(doubt it)
Piers
Well-known member
Thanks kashurst. I'll do this as soon as I'm back on board. I'm on my way to South Africa for two months (waiting in Amsterdam for the mid-afternoon Emirates flight) whilst Play d'eau is having some work done on her in Southampton (http://www.playdeau.com/play-deau-and-south-africa/).
dp24
New member
This is perhaps just a simple electrical question about RCDs but:
Assuming a 'plastic' boat up on shore with no metal connection to earth...
Where does the residual current current go in order for an imbalance within the RCD?
Would an RCD be of any use without an earth connection if, for example, a live wire came in to contact with the metalwork in the boat (which is not earthed)?
If the RCD wasn't tripped by this initial contact, I assume all the bonded metalwork would become live and anyone touching it while standing on the ground would get a shock (until the RCD kicked in).
Assuming a 'plastic' boat up on shore with no metal connection to earth...
Where does the residual current current go in order for an imbalance within the RCD?
Would an RCD be of any use without an earth connection if, for example, a live wire came in to contact with the metalwork in the boat (which is not earthed)?
If the RCD wasn't tripped by this initial contact, I assume all the bonded metalwork would become live and anyone touching it while standing on the ground would get a shock (until the RCD kicked in).
Hurricane
Well-known member
Just a thought
What would be the implication of forgetting to break the switch when the boat goes back in the water?
What would be the implication of forgetting to break the switch when the boat goes back in the water?
David2452
Active member
It would negate the ITs galvanic protection as your PE would be then be connected directly to the shore PE.
jfm
Well-known member
None as regards safety. But your boat metal would be copper connected to your neighbour's and you could be the anode in a multi-boat electrolysis system. Basically, you would have disabled the protection that your isol transformers are meant to give you.
On my boats there has always been a warning light on the dash so even if forgetful I'm unlikely to leave the switch on for very long, and even a month is probably no big deal!
kashurst
Well-known member
the residual current is going into another conducting (or partially conducting) object -The RCD would detect that more than 30milliamps of current was not being returned and immediately shut down. if there was a genuine electrical fault on board to an exposed metal part and the boat wasn't earthed and you touched it you would feel a very small shock for a fraction of a second - a few hundred milliseconds. Probably enough to make you go "ouch", approximately 1 -2 joules of energy. Walking across a nylon carpet and touching a filing cabinet will feel worse. An RCD doesn't need an earth connection to work - it just measures the difference in current between the live and neutral wires. If everything is OK then the current out will equal the curent returned (more or less).
An RCD is a better safety device than an earth connection. With an earth connection you are relying on a fuse or circuit breaker to blow - these are usually 10 amps plus and can take quite a bit to make them trip out - more than enough to do you serious damage. Humans conduct electricity quite well but possibly not well enough to blow a fuse/breaker and you can get a serious and sustained shock without the fuse blowing (I know from experience).
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dp24
New member
Thanks, I think the inner workings of an RCD is a really elegant system for detecting current leak.
If, for example, the live wire came in to contact with the prop shaft in the engine room without any connection to earth, would the intrinsic capacitance of the metal be enough to trip the RCD or would it remain live until someone came along and touched (earthed) the prop?
After all, for there to be a residual current, some must leak to somewhere, I just can't get my head around is earth is required for sufficient leak.
kashurst
Well-known member
for an electrical current to flow there has to be a potential difference (voltage) - we tend to get hung up on the idea of a circuit or path that the electricity flows around, which is generally what happens, however if another possible conductor is close by/touching that path and it is of a different electrical potential then some current will flow that way. - if the electrical potential is large enough the other path need not even be touching - resulting in arcing, sparks or lightning etc.
an earth is not neccesarily required to have electrical leakage, also if an earth is fitted it doesnt follow that any leakage will always take that path. I don't think the prop shaft in proximity to the rest of the metal parts in the boat or the ground would have sufficient capacitance to absorb enough charge, to create enough of a current to trip the RCD. So, yes, someone would get a surprise in your scenario, but as long as the RCD is working all would be well.
However such an eventuallity is very unlikely - boats are usually pretty good electrically speaking. - actually no they are pretty rubbish as the connections get worse over time but generally in a safe "its not working" way, wires tend to stay in place.
the term residual comes from the idea that normally with no fault the current in minus the current out should be zero. If a fault occurs it may still be zero, however once a new electrical leakage path is available (ie a human touching an exposed circuit) there will be a difference in current in and out - a residual current. sorry if I am labouring this.
an earth is not neccesarily required to have electrical leakage, also if an earth is fitted it doesnt follow that any leakage will always take that path. I don't think the prop shaft in proximity to the rest of the metal parts in the boat or the ground would have sufficient capacitance to absorb enough charge, to create enough of a current to trip the RCD. So, yes, someone would get a surprise in your scenario, but as long as the RCD is working all would be well.
However such an eventuallity is very unlikely - boats are usually pretty good electrically speaking. - actually no they are pretty rubbish as the connections get worse over time but generally in a safe "its not working" way, wires tend to stay in place.
the term residual comes from the idea that normally with no fault the current in minus the current out should be zero. If a fault occurs it may still be zero, however once a new electrical leakage path is available (ie a human touching an exposed circuit) there will be a difference in current in and out - a residual current. sorry if I am labouring this.
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dp24
New member
Thank you for taking the time to explain it all.
So back to start of the thread, without earthing the boat (fe. throwing the isolator bypass switch) the metalwork could become live, despite the RCDs. However the subsequent risk from this live metalwork is low with the RCDs protecting you.
Think I'd prefer for the original fault to trip the RCD!
