Tripping marina RCD (Current Device, not Craft directive!)

[Gibbo]

Look folks, all this argy bargy about who is right or wrong is quite frankly nice to observe to see who cracks first, but for those of us who dont have a clue when it comes to electics, all we need to know is, ....what the chuff are you all going on about? pics would be really helpfull of elctical systems and not the wierd electric circuit diagrams which nobody understands unless youve been taught about them.

 

What the chuff does a GI look like(an not the US marine version)? What does a IT look like and how and where should they be fitted. Even if the jury is out on their effectivness, better to fork out some pennies than to erode the hull or BBQ oneself bankside.

 

Im going from wood to steel. The only things i ever had to worry about prior to this was Worm and fresh water

 

I'm afraid the only answer to that is that if one cannot understand a simple wiring schematic then one does not have the required knowledge to install the equipment. Get someone else to do it.

 

Sorry.

 

Gibbo

[bottle]

Salty

 

If your new boat is to have a connection to landbased mains, then you have the choice of fitting the 'Galvonic Islator' or an 'Isolation Transformer' (GI cheaper than IT)

 

If you are not going to be using landbased mains (an extension lead from shore) then they are not required.

 

If you fit one (advise qualified/competant person) they are the first item after the plug, on the boat, that the landbased mains is connected to.

 

I was going to post some pictures but they just look like metal boxes If you wish to see them go to google and search the images

[tomsk]

Please charge the installation/modification of anything electrical to a qualfied electrician.... Thank yew

[blackrose]

And now onto the slightly more tedious subject of the RCD tripping when it shouldn't.

 

The boat RCBO tripped twice today, once when I plugged the washing machine into a socket and later when I switched on the same socket where the TV was already plugged in. Both times I reset the RCBO and it was fine. This has happened before but not for several months.

 

The first time I asked this question the consensus was that if this happens one should seek the cause rather than just resetting the RCD or RCBO. The last time I brought the subject up I was told that the RCBO is sensitive and was just doing its job.

 

In hindsight, I can see that the latter answer is clearly wrong - the job of an RCD or RCBO is not to trip unnecessarily! Unless of course there is a fault, in which case why doesn't it happen again as soon as I reset it?

[chris w]

And now onto the slightly more tedious subject of the RCD tripping when it shouldn't.

 

The boat RCBO tripped twice today, once when I plugged the washing machine into a socket and later when I switched on the same socket where the TV was already plugged in. Both times I reset the RCBO and it was fine. This has happened before but not for several months.

 

The first time I asked this question the consensus was that if this happens one should seek the cause rather than just resetting the RCD or RCBO. The last time I brought the subject up I was told that the RCBO is sensitive and was just doing its job.

 

In hindsight, I can see that the latter answer is clearly wrong - the job of an RCD or RCBO is not to trip unnecessarily! Unless of course there is a fault, in which case why doesn't it happen again as soon as I reset it?

 

 

Is there the possibility of damp having crept into the offending socket?

 

Chris

[Scotty]

Good theory, or maybe damp in the appliance?

[Gibbo]

The biggest problem with RCDs is that they work.

 

Not very helpful, I know.

 

Gibbo

[smileypete]

And now onto the slightly more tedious subject of the RCD tripping when it shouldn't.

 

The boat RCBO tripped twice today, once when I plugged the washing machine into a socket and later when I switched on the same socket where the TV was already plugged in. Both times I reset the RCBO and it was fine. This has happened before but not for several months.

 

The first time I asked this question the consensus was that if this happens one should seek the cause rather than just resetting the RCD or RCBO. The last time I brought the subject up I was told that the RCBO is sensitive and was just doing its job.

 

In hindsight, I can see that the latter answer is clearly wrong - the job of an RCD or RCBO is not to trip unnecessarily! Unless of course there is a fault, in which case why doesn't it happen again as soon as I reset it?

Hi,

 

Was the washing machine plugged into another socket when the second trip occured? Also are there any kettles, water heaters, surge protectors, plugged in on the same circuit? Do you know if the circuit is a ring or radial at all?

 

 

Assuming you're competent to work on mains electrics:

 

If it's not a dodgy heater element, appliance etc, I would start by looking for any loose connections behind the socket.

 

Next I'd trip the RCBO by using the test button, disconnect the shoreline, unplug everything from the sockets, and measure the resistance between live to earth and neutral to earth on that ring or radial. Ideally this should be done with a 'megger' that tests the resistance at high voltage.

 

Next I'd look for any loose connections in the radial or ring between the socket and the RCBO, and even the connections between shore inlet, main switch and RCBO itself.

 

I'd even consider swapping the socket with another one (single pole switching), just in case.

 

Failing that I'd just try another RCBO. But if you don't really want to go to all the trouble of the above, you could just try another RCBO first.

 

All in my humble opinion

 

cheers,

Pete.

 

Edit:

 

Some useful reading here:

 

http://www2.theiet.org/Publish/WireRegs/Wi...anding_rcds.pdf

Edited October 12, 2007 by smileypete

[John Orentas]

Blimey this has been going on for a while. I suspect this problem is occurring because there are two or more RCD's in series in the same circuit, (marina and boat in this case) the problem has been known about for as long as they have been produced and many manufacturers warn against it, as to why they appear to talk to one another, I have never seen a rational explanation.

[blackrose]

Is there the possibility of damp having crept into the offending socket?Chris

Could be, the back of the socket is very close to the steel but there's a quarter inch of sprayfoam between.

Hi,Was the washing machine plugged into another socket when the second trip occured? Also are there any kettles, water heaters, surge protectors, plugged in on the same circuit?

Yes and yes.

Do you know if the circuit is a ring or radial at all?

It's a ring mains

Assuming you're competent to work on mains electrics:If it's not a dodgy heater element, appliance etc, I would start by looking for any loose connections behind the socket.

I checked that some time ago and I'm confident there aren't any loose connections there.

Next I'd trip the RCBO by using the test button, disconnect the shoreline, unplug everything from the sockets, and measure the resistance between live to earth and neutral to earth on that ring or radial. Ideally this should be done with a 'megger' that tests the resistance at high voltage.Next I'd look for any loose connections in the radial or ring between the socket and the RCBO, and even the connections between shore inlet, main switch and RCBO itself.I'd even consider swapping the socket with another one (single pole switching), just in case.Failing that I'd just try another RCBO. But if you don't really want to go to all the trouble of the above, you could just try another RCBO first.All in my humble opinion cheers,Pete.Edit:Some useful reading here:http://www2.theiet.org/Publish/WireRegs/Wi...anding_rcds.pdf

Thanks

Blimey this has been going on for a while. I suspect this problem is occurring because there are two or more RCD's in series in the same circuit, (marina and boat in this case) the problem has been known about for as long as they have been produced and many manufacturers warn against it, as to why they appear to talk to one another, I have never seen a rational explanation.

It hasn't happened for some time. Perhaps it's just the weather and some damp as Chris says. I always thought there was always supposed to be a breaker on the boat and on the supply side? Edited October 12, 2007 by blackrose

[smileypete]

Hi,

 

One other thing, what's the current overload trip rating of the RCBO? Is it being loaded at or near it's overload trip current?

 

Edit: In addition to the above post something I'd consider doing is breaking the ring to give a radial with two legs, as long as the cable and RCBO rating and circuit loadings allow it. If there are any wierd capacitance/impedence effects then having a ring may exacerbate them.

 

cheers,

Pete.

Edited October 12, 2007 by smileypete

[GUMPY]

Blimey this has been going on for a while. I suspect this problem is occurring because there are two or more RCD's in series in the same circuit, (marina and boat in this case) the problem has been known about for as long as they have been produced and many manufacturers warn against it, as to why they appear to talk to one another, I have never seen a rational explanation.

 

Can you provide any documented evidence from a reliable source, such as the IEE, of this John?

 

I have never heard of this until you bought it up and have been working with mains voltages all my life.

 

We have hundreds of RCDs in our equipment and have never had an occurrence of this.

 

Even on my boat there are 3 RCDs between the supply and the user in 5 years never had one nuisance trip!

 

Julian

 

wanting to be enlightened with some hard evidence

[blackrose]

Hi,One other thing, what's the current overload trip rating of the RCBO? Is it being loaded at or near it's overload trip current?Edit: In addition to the above post something I'd consider doing is breaking the ring to give a radial with two legs, as long as the cable and RCBO rating and circuit loadings allow it. If there are any wierd capacitance/impedence effects then having a ring may exacerbate them.cheers,Pete.

It's 16 amps which is the same as the shore power supply. I've tripped it by overloading a couple of times but I'm sure that wasn't the reason last night or this morning.

Even on my boat there are 3 RCDs between the supply and the user in 5 years never had one nuisance trip!

Never? Are RCBOs more sensitive than RCDs because in two years I reckon I must have had 20 or 30 nuisance trips. Edited October 12, 2007 by blackrose

[Yoda]

For my two pennyworth, I have noted that on connecting an inductance or capacitance load, the system has tripped out. I have tried it several times in different sockets to try and isolate any problem but its what the RCD sees and reacts to. There has been no fault with the load.

Edited October 12, 2007 by Yoda

[blackrose]

I have noted that on connecting an inductance or capacitance load, the system has tripped out.

 

And what is an inductance or capacitance load in laymans terms? (Or are those already laymans terms? ) What sort of appliances would they include?

 

Also is there some conflict with the RCBO and a socket extension with surge protection as Pete suggested earlier? I once blew up a socket extension with surge protector on another boat when I had one plugged into my mains ring that I was running from a generator.

[GUMPY]

Never? Are RCBOs more sensitive than RCDs because in two years I reckon I must have had 20 or 30 nuisance trips.

 

Should be the same sensitivity

 

There has never been a trip where I haven't known the reason for it, I dont class that as nuisance.

Normaly its a neutral earth short when I am working on part of the electrics, with only a single pole MCB disconnected on the circuit I am working on.

 

J

[carlt]

Mine trips every time I stick one finger in the live hole and another in the neutral. Is there any way of overriding it?

[chris w]

Mine trips every time I stick one finger in the live hole and another in the neutral. Is there any way of overriding it?

 

Try an overdose - it doesn't mess up your hairstyle

 

Chris

[Scotty]

I guess it's a 30mA RCBO? And not something obscure and over sensitve?

 

Mine trips every time I stick one finger in the live hole and another in the neutral. Is there any way of overriding it?

Have you got small fingers or big holes?

 

 

Don't answer that

[blackrose]

I think there's possibly an issue with the back of 2 sockets being too close to the steel on my boat. They're both above gunwhale height where the gap between the lining and steel is at its narrowest. Although theres sprayfoam behind and the sockets are in the white plastic backing boxes, perhaps dampness is the problem.

 

I'm going to cut out wooden rectangles or make something from oak stripwood to mount the sockets on so I can bring them out by half an inch and get some more foam in there - or is there a decorative mounting for a double socket I can buy?

[stylus]

I am looking here for some advice from the professional and experienced electrical buffs here.

 

I have formed my own opinion about the situation but sometimes I find that once an idea is set in my head it gets difficult to think along different lines.

 

My boat is fitted with a Heart Interface Freedom 20 Inverter /charger, 2KVA continouus rating

This is a power sharing type of inverter/charger.There is a setting for the maximum current drawn from the shoreside source, currently set to 10 amps (pun not intended): If any extra output is required that would require a greater input current than this, the inverter would make up the difference from the batteries; useful for coping with equipment requiring a high starting current, does not trip the shore mcb.

I do not have an isolating transformer and deem a Galvanic Isolator as unnecessary as I only plug into the shore power for a few hours once every two or three weeks.

I believe that of all the boats at these moorings my boat is the only one with a power sharing inverter/ charger of this type

 

Incorporated in the device is a powered contact linking the inverter neutral line to earth when there is no shore power connected. Together with the on board rcd this provides the necessary protection. When the shore power is connected, the shoreside earth line is connected to the boat earth line, and the contact linking the earth line to the boat neutral opened (by the contactor). This is all as it should be for personal saftey in both circumstances.

 

My problem is this. When connecting up to shore I frequently trip the shoreside RCD which greatly annoys everyone as it cuts off all the power to the workshops as well as all the other boats. I have discovered that this appears only to happens when my steel hull is in contact with the steel piling.

Once up and running on shore power it is OK for the hull to touch the piling.

 

I have checked through the system all connections are connected the right way round.

When running on the inverter, using a DVM, the voltage between N & E is practically zero (mV’s) and full 220V between L & N and L & E. Similarly when on shore power.

When on shore power, with the earth wire at the shore plug disconnected, the readings between N-E and L-E become indestinct indicating that the earth is floating which indicates that when connected, the shore earth line is OK.

 

I have of course been unable to take readings at the instant of plugging in the shore power.

 

I surmise the following: My inverter takes a moment to identify that the shore supply is plugged in. During this time the on board N-E link remains connected and the shore N and E lines are also connected at the shore transformer). If the hull is touching the piling, the earth path to the shore earthing point (connected to the same piling) is of lower resistance than the neutral wire to shore where it is connected to the shore neutral, passing through the shore rcd on its way. The resulting current inbalance in the L and N wires in the shoreside rcd cause it to trip.

When the contactor in the Inverter/charger operates, (which it does when the hull is not touching the piling when the shore line is being connected), everything is ok, even when the hull touches the piling later.

 

In your opinion is this likely to be a correct conclusion?

If it is, how do I suggest to the yard owner that his earth system is too good (or the gauge of his wiring too small) without annoying him any further?

I have thought of fitting a contact breaker that would break the boat N-E link before applying shore mains power to the inverter unit. However this would only introduce an extra possibleity later for bad connection in the earthing system.

 

I am thinking that an isolation transformer would be the best solution. Most isolating transformers are expensive and heavy. I feel this should resolve the problem, and parhaps reduce the little amount of galvanic corrosion I get.

Do you think this one would be suitable? http://www.airlinktransformers.com/transfo...transformer.asp Do you think it will need a surge limiter?

 

Rgds

[stylus]

Hi

There are 3 types of RCD tripping units I know of. They are marked A,C or D after the currant rating of the RCD. I have found that the ones marked A or C are more prone to tripping on start up currants than the ones marked up with a D.

Might be worth checking.

Isolation Transformer = 2 matched coils on a common iron former insulated from each other, one coils magnetic field is induced into the other coil. i.e 240volts in 240volts out.

The earthing on mine is not decoupled from the mains earthing so I still need a galvanic isolator.

Removing the earth could be dangerous as if a nuetral fault occured on the boats wiring, the boat hull could become live and anybody touching the boat and an earthed walkway or even a swimmer touching the boat in certain surcumstances could get a shock.

There are some websites you can visit. Just type in- What is an Isolation Transformer ?

Regards

Stylus

[GUMPY]

Isolation Transformer = 2 matched coils on a common iron former insulated from each other, one coils magnetic field is induced into the other coil. i.e 240volts in 240volts out.

The earthing on mine is not decoupled from the mains earthing so I still need a galvanic isolator.

 

In which case if it is a true isolation transformer then it is wired incorrectly.

A simple and easy thing to fix.

 

Have a look here on how it should be wired

http://www.smartgauge.co.uk/iso_wire.html

 

There are other types of transformer that do not isolate (auto transformers) and have a neutral that is connected straight through.

 

Julian

[chris w]

Hi

There are 3 types of RCD tripping units I know of. They are marked A,C or D after the currant rating of the RCD. I have found that the ones marked A or C are more prone to tripping on start up currants than the ones marked up with a D.

Might be worth checking.

Isolation Transformer = 2 matched coils on a common iron former insulated from each other, one coils magnetic field is induced into the other coil. i.e 240volts in 240volts out.

The earthing on mine is not decoupled from the mains earthing so I still need a galvanic isolator.

Removing the earth could be dangerous as if a nuetral fault occured on the boats wiring, the boat hull could become live and anybody touching the boat and an earthed walkway or even a swimmer touching the boat in certain surcumstances could get a shock.

There are some websites you can visit. Just type in- What is an Isolation Transformer ?

Regards

Stylus

 

You are getting confused with Miniature Circuit Breakers (MCB's). Type D is a particular type of MCB which is NOT an RCD. The Type D MCB is for large inrush currents.

 

You should be using a type AC RCD which detects AC current earth leaks or a type A RCD which also detects DC leakage current. (There is also a type B but this is for rectified 3 -phase supplies and so not applicable to your narrowboat.)

 

Chris

[blackrose]

I think there's possibly an issue with the back of 2 sockets being too close to the steel on my boat. They're both above gunwhale height where the gap between the lining and steel is at its narrowest. Although theres sprayfoam behind and the sockets are in the white plastic backing boxes, perhaps dampness is the problem.

 

I'm going to cut out wooden rectangles or make something from oak stripwood to mount the sockets on so I can bring them out by half an inch and get some more foam in there - or is there a decorative mounting for a double socket I can buy?

 

I changed the problem socket on my boat the other day and it seems to have solved the nuisance trips. I wonder what was wrong with it?