Portable Genny - Worth bothering with?

[jimbaerselman]

Joe, your alternative (better titled) thread seems to have died. But I'm sure you're a better arbitrator than I on these things, so here are are a few conclusions which seem to result from the discussion:

1. RCDs don't work unless earth is connected to 'neutral'

2. The more distant the earth/neutral connection, the more likely that an RCD will trip due to faults/leakages outside your premises/boat.

3. ? If you have no RCD, it's often safer to make sure that earth and neutral are not connected - anywhere along the line - which includes supply and consumer items. (fully floating system).

4. The more items are connected, the more difficult it is to ensure there's no E/N leakage in a floating system

5. If you have no RCD, and you're using a distant earth, you must be absolutely sure that your supply can't be reversed anywhere down the line (watch out in continental Europe!). And since that is a risk (even though it can be monitored), you should be equally sure that there is absolutely no leakage on your boat from 'neutral' (now live!) to 'earth' (which, out of the water, could be your prop shaft).

6. Since 4 and 5 are difficult to monitor (though we've seen suggestions above), you're better off fitting an RCD and ensuring earth and neutral are connected, rather than working with a fully floating system.

7. A local Earth/Neutral connection gives less likelyhood of false RCD trips.

This isn't a complete picture (no talk about isolating systems) but have I gone of the rails at all?

 

[Anonymous]

Jim,

1. Is completely untrue. It is true that a return current is required for someone to get a shock but it is untrue that you have to deliberately connect your wiring to Earth, make an RCD work.

Connecting N and E is, as a rule, a bad, bad, bad idea and could damage everything metal below the waterline as well as cause a fire in the wiring. Measure the voltage between E and N on a number of marina supplies. The voltage can be tens of volts and you intend to short that out locally, via your wiring, on your boat!!?? /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif

For most practical purposes, even with only a two wire wire system, an RCD will provide highly effective electric shock protection for everything downstream of the RCD. An RCD does not - I repeat does NOT - need to be earthed to give protection. Mind you, if you don't run an earth wire to it, you can't test it with the internal tester but that is a completely separate issue.

 

[Guest]

Reading all this - despite going off the original posters question ... is making me think ...

Now as I understood it an RCD works on the Residual current that prevails across circuitry to earth ... and if this changes by a set amount or goes over an amount - TRIPS.

An MCB or Breaker does not and needs a larger amps amount - as in a fuse to trip.

The post saying that earth does not need to be connected for an RCD to work seems to be contrary to what I was told ...

 

[rogerthebodger]

[ QUOTE ]
Now as I understood it an RCD works on the Residual current that prevails across circuitry to earth ... and if this changes by a set amount or goes over an amount - TRIPS.

[/ QUOTE ]

Yes that is one way to look at it. The "Residual Current" or a I look at it the differance in the current in the live and neutral of over 30mA would cause the RCD to trip.

If as Lemain says no earth connection is needed where dose that current go.

Is I have said before it goes down to earth or sea and back to the neutral of the supply through the earth to neutral connection at the generator, inverter or substation

With shore power that connection is at the substation. On a boat that connection must be made at the generator.

I had a look last night for the book you posted but I dont have a copy but I did look in Charlie Wing book on electrical wiring and he has the same info as Calder and also shows how to connect neons to show if the line and neutral is reversed on the shore power connector.

It may be this point that the book you refered to about swimmers is refering to.

Do you have the ISBN number and then I can order it to check is referances.

 

[Guest]

ISDN ... mmmm not immediately to hand ... but here it is listed by Amazon ...

http://www.amazon.co.uk/Practical-Boat-Owners-Electrics-Afloat/dp/0713661496

You should be able to glean enough info from there to sort an ISDN or whatever ...

The point about the swimmer was that earthing to sea could create a lethal environment around your boat if a trip doesn't work ..

As to marina earthing - I agree that some are not so good as others - especially if travelling to some suspect areas ! But then how do you combat all eventualities ? Surely a solution in Solent may not be answer to a berth in Greek islands or whatever ?

Come over here and see the mess in houses ... I took over a large esatate with house that has no earth at all .. luckily we can ENR (earth neutral return) as the substation has been updated to EU standards ... pity about the overhead cables are still original Soviet !!

We had fun and games when we bought the emerg. genny - B&S 3.5KVA job ... we needed to find out about polarity etc. and also way to earth it out - we meeded to have it pluggable into house systems without incurring polarity problems ... The house of course doesn't help - as it has 2 separate circuits feeding 2 meters. So we couldn;t feed in to the single ... as that would have powered Electric Co's meters !! Don't ask more !! It's a horror story .. that took ages to sort out ...

 

[Anonymous]

[ QUOTE ]
If as Lemain says no earth connection is needed where dose that current go.

[/ QUOTE ]Lemain says that if there is no current you don't get a shock so what's the problem? If there is a potential of getting a shock then there must be a return path by some means simple, complex, designed, accidental or fault and in that case the RCD will protect you. You don't need a device to protect you when there is no possibility of getting a shock.

You don't need to make a purposeful, or intended connection and by so doing all you do is to INCREASE the risk of a shock. If the genny is isolated the chances are that you will never get a shock unless you connect yourself between L and N.

 

[rogerthebodger]

Thanks for the book ref. I was going to buy from amazon anyway

Yes living in the 3 rd world african country I see all kind of "Electrical installations" The current standard supply connection is to wire your :house" shak to the street light outside on the road.

We have had alot of power outages this winter so lots of people have got standby generators !!!! and like the guys who died in the UK floods by missusing a petrol pump we have had people filled by the same and bad generator installation.

This is why I get very concerned with bad / incorrect connection practice.

 

[rogerthebodger]

Then there is not point of installing a RCD because as you say there cannot be any leakage current, no difference in current in live and neutral to cause RCD to trip so not point in installing RCD

 

[Anonymous]

[ QUOTE ]
The point about the swimmer was that earthing to sea could create a lethal environment around your boat if a trip doesn't work ..

[/ QUOTE ]I find that hard to believe. If your stanchions and brightwork are allowed to go live then you could get a nasty belt when getting back on board from swimming - that is a very real risk if they have been connected together and incorrectly grounded. They should all be connected to seawater earth which does not necessarily have to be connected to a generator's earth.

 

[rogerthebodger]

I also find it hard to beleave but I have ordered the book nigel refered toso as to find out his theory behind the comments and "to do my own investigition"

In my case my stanchions, handrails all stainless steel are connected together that is why I am very particular about grounding of internal mains supply systems and have investigated then alot. This is why I have come to the conclusions I have together with my too many years of engineering training and experence

 

[Anonymous]

[ QUOTE ]
Then there is not point of installing a RCD because as you say there cannot be any leakage current, no difference in current in live and neutral to cause RCD to trip so not point in installing RCD

[/ QUOTE ]Yes, an RCD in a floating system might be overkill but if you are connecting the genny to your marina shorepower input then there will be an RCD on the consumer unit. Someone was saying that you had to have that connected to Earth, thus losing all the benefits of the naturally-safe floating supply. You don't need to, and that's all I've been saying!

 

[rogerthebodger]

You dont get it

It is me who says that for a RCD to work there MUST BE an alternate path for the leakage current to flow back to the neutral of the generator for the RCD to trip.

That alternate path will be through earth and to complete the circuit the earth and neutral MUST be connected at the generator even if it is pluged into the shore power inlet socket.

If there is not alternate path (no earth connection you may not a shock to earth and if there is a fault between live and earth the RCD will not trip and the overload or fuse may not blow due to bad / no earth.

This could make the steelwork live and this is the potential for the danger to the swimmer.

A RCD WILL NOT TRIP UNLESS AN ALTERNATE PATH AROUND THE RCD BACK TO THE NEUTRAL SUPPLY EXISTS

IF YOU HAVE A FLOATING CIRCUIT A RCD IS POINTLESS

If now 17-00 hrs and I am leaving the office so will not be online to tomorrow.

Good Night

 

[jimbaerselman]

My aged brain is now working overtime.

An RCD detects a current difference between the L and N lines.

A current difference is not caused if Jim attaches himself to both live and neutral lines. Currents would be equal, and he'd fry until any over-current device kicks in. Get the de-fibrillator out.

If the neutral line is similar potential to 'earth' (wot I'm standing on) through some connection (which I daren't define yet), and I am touching a live wire, I may conduct a current. If so, this would cause less current to flow back through the neutral than the live, thus tripping the RCD.

The residual current would be returning via the environment, rather than through the green and yellow wire (UK). So the G/Y wire is redundant for the RCD function in this case.

However, for this to take place, there must be some connection of the neutral to mother earth somewhere, otherwise 'live' would not be live relative to mother earth.

This connection could be at a substation, at the premises threshold, at a distribution box, just downstream of an isolating transformer, or at the point of use. But it has to exist, otherwise there's no potential difference between a 'live' wire and mother earth (not the wire).

What is vital is that the RCD is downstream of where the N line is earthed.

So, question, do multiple earths (one remote, one local), hinder the operation of RCDs? Do they introduce weird phase differences and funny impedancies which I don't understand?

I'm not onto isolating tranformers yet - or corrosion. At that level I found Gothic29' contribution of wiring diagrams most useful [ QUOTE ]
See :-

http://www2.theiet.org/Publish/WireRegs/WiringMatters/

Then scroll down to "Marinas and Similar Locations". It's under the title "Issue 23 Spring 2007"



[/ QUOTE ]

 

[captainslarty]

[ QUOTE ]
Joe, your alternative (better titled) thread seems to have died. But I'm sure you're a better arbitrator than I on these things, so here are are a few conclusions which seem to result from the discussion:

1. RCDs don't work unless earth is connected to 'neutral'

<span style="color:red"> Not true Jim, the rcd will monitor the balance of L and N. If out of balance a leakage must be occurring to earth. That earth could be a steel hull with you touching it etc, current takes the easiest path</span> .

2. The more distant the earth/neutral connection, the more likely that an RCD will trip due to faults/leakages outside your premises/boat.

<span style="color:red"> Not necessarily the distance, more important is that the NE connection is upstream of the RCD </span>

3. ? If you have no RCD, it's often safer to make sure that earth and neutral are not connected - anywhere along the line - which includes supply and consumer items. (fully floating system).

<span style="color:red"> Personally I dont agree Jim, Back to the steel hull analogy, the stantion etc, the earth passage is through the stantion, the hull to the water, without a reference point the voltage cannot be zero or thereabouts in respect to earth, and it is the difference that kill you by allowing a current pathway </span>

4. The more items are connected, the more difficult it is to ensure there's no E/N leakage in a floating system

<span style="color:red">True, however I personally cannot advocate a floating system for the above reasons. Even if you disconnect the earth at the marina plug the neutral is connected at some point, or should be, a path to earth is then probable, the system no longer floats, it is reference to the neytral, ground upstream (I may be misunderstaning your definition of floating though Jim </span>

5. If you have no RCD, and you're using a distant earth, you must be absolutely sure that your supply can't be reversed anywhere down the line (watch out in continental Europe!). And since that is a risk (even though it can be monitored), you should be equally sure that there is absolutely no leakage on your boat from 'neutral' (now live!) to 'earth' (which, out of the water, could be your prop shaft).

<span style="color:red"> Yes, that is the reason why the NE connection is upstream, NEVER on the boat. I dont see how you could ensure no leakage when you and the hull could become the pathway.. ouch ! </span>

6. Since 4 and 5 are difficult to monitor (though we've seen suggestions above), you're better off fitting an RCD and ensuring earth and neutral are connected, rather than working with a fully floating system.

<span style="color:red"> Absolutely, but with the caveat that the E and N connection is upstream (at the source - genny or shorepower or inverter , the RCD is a line of defense, but not infalible. I cannot see the logic in a floating system at all . Also, it is best to test the connection prior to plugging in in the first place</span>

7. A local Earth/Neutral connection gives less likelyhood of false RCD trips.

<span style="color:red"> Not sure exactly what you mean by a local connection, upstream (at the point of feed as said above is what is needed) </span>

This isn't a complete picture (no talk about isolating systems) but have I gone of the rails at all?

[/ QUOTE ]

<span style="color:red"> Not at all, I am sure anyone reading this thread is as baffled as the rest of us lol </span>

 

[Guest]

[ QUOTE ]
[ QUOTE ]
The point about the swimmer was that earthing to sea could create a lethal environment around your boat if a trip doesn't work ..

[/ QUOTE ]I find that hard to believe. If your stanchions and brightwork are allowed to go live then you could get a nasty belt when getting back on board from swimming - that is a very real risk if they have been connected together and incorrectly grounded. They should all be connected to seawater earth which does not necessarily have to be connected to a generator's earth.

[/ QUOTE ]

I have been loose in the comments on this and refer all to A. Garrods book where the subject of electrocuting a swimmer is covered ... it was also covered by PBO many moons ago ....

It's all to do with how to connect and bond / earth your shore power etc. The different methods and pro's / cons of each way.

I am sure that the likelihood of killing a swimmer is extremely unlikely eevn if 240 did hit the earthing to sea !! They'd have to be very close to each other ...

 

[rogerthebodger]

That's how I see it

I think Lemain's point is if you have an isoluated systen (No neutral connection) if a person touches the line because the neutral in not connected no current will flow no shock.

This is potential correct but only if there is no possibility of the neutral also having a faulty connection to earth.

The other point is that if the line or neutral has a leak to earth the RCD would not trip as you say ao no fault would show up and you would have a live piece of equipment without knowing it.

of the advantages and disadvantages of a floating or earthed / neutral system IMHO the earthed neutral system outways the floating system and as nost people, power distribution compained and all the published docs I have found recomend an earthed systen plus my own logic and experance there is only one way to go earth neutral system.

This thread is becomming another anchor type thread.

 

[jimbaerselman]

Many thanks for your careful answer Joe. As you'll see from my later post, I'd hoisted some of your points aboard already.

Being pedantic, I'm still convinced that for a 'live' wire to be a threat, there must be, somewhere, a connection of another phase to ground. As in all normal mains supplies. Otherwise there's no circuit. In other words, N, in all normal mains supplies, is grounded somewhere, however far away. Otherwise L isn't live relative to earth - and isn't a threat. This is what I meant when I said 'N must be connected to E for RCDs to work'

If there is no grounding of any phase, you've got a fully floating circuit, in which the only threats occur through connecting two phases. Examples of fully floating circuits relevant to the yachtsman are:

1. A portable genny in which neither phase wire is connected to the genny frame or the earth line input (rare, but I have found one!)

2. The two phase outputs of an isolating transformer when there is no earth or frame connection.

I note that the Institute link (which I repeated in my previous post) always recommends an earth connection to one phase immediately downstream of an isolating transformer before the RCD (and, incidentally, the wiring diagrams in that link imply that previous earth links should be broken, though I don't know why this should be so).

So, I think I'm there, and I think we have different understanding of what a fully floating system is - it's a system in which there is no connected path to earth for any phase. Such a system can be checked by finding a sound earth (the water) and checking to see if there is any voltage present between that earth and either of the supply lines.

The problem with fully floating systems is ensuring that when you plug a consumer item in, you don't inadvertently create an earth through that item's frame or whatever . . . so, no, I don't like the idea of fully floating.

So, back to the thread subject. Personally, I'd check that portable genny to see if it had an RCD built in. If it did (many do), I'd assume 'frame' was connected to one phase before the RCD (that phase is now N, but only with reference to the frame). I'd then earth the frame (as per manufacturere's recommendations) to make sure that N is neutral relative to mother earth (water) as well.

 

[Richard10002]

[ QUOTE ]
This thread is becomming another anchor type thread.

[/ QUOTE ]

I, (and I'm sure many others), find the anchoring threads, (and this one), extremely interesting.

Both subjects are of extreme importance to "us" and the wealth of information and diverse opinion available here has enabled me to make some fairly important decisions, even though some may disagree with what I might choose to do.

On anchors, I am definitely going to buy a 33kg Rocna, if I can get one, or a Spade of similar weight.

On the genny, I dont pretend to understand much of what has been said, but will sift through it and do something about the earth when I decide to make the genny part of my day to day kit.

In the meantime, I've got it going, (after it has sat for about 2 years in the bottom of a locker), and will be using it carefully, (a la Lemain), to make sure that it is a good alternative to using the main engine to charge the batteries).

Just need to make a converter cable to connect it to the marina input, and we'll see how it works.

Thanks to all for contributing... looks like I opened a can of worms which I'll be digesting later.

Richard

 

[rogerthebodger]

[ QUOTE ]
I note that the Institute link (which I repeated in my previous post) always recommends an earth connection to one phase immediately downstream of an isolating transformer before the RCD (and, incidentally, the wiring diagrams in that link imply that previous earth links should be broken, though I don't know why this should be so).


[/ QUOTE ]

I have seen when isolation transformers are fitted the incomming earth is connected to the frame of the transformer and the secondry neutral is connected to the local earth but seperate from the incomming earth.

One of the functions of an isolation transformer is for galvanic isolation and then the local earth must be DC isolated from the marina earth

 

[Guest]

One thing that gets forgotten with Gennys ...

Regardless of all above ... if it is not started and used regularly - you can end up with a useless bit of kit - engine will work - but no generation of electrics as the magnetic part has died ! So I was told by dealer anyway !! He specifically warned me against leaving my emerg. genny unused for too long. He even went further and reckoned it should be put on load - not just started.