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To B or not to B the RCCB


The Ents
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Hi All,

My Marina power provider has just fitted a new unit in the main supply. My boat now trips the main RCD at 3.30 in the morning, three days running! Everything goes off including the freezers in the cafe.

I am in the doghouse and disconnected from the supply.

So where do I start? Yesterday i made up a new shoreline, did some simple tests for shorts with a normal DVM and found nothing obvious. I then had the Stirling inverter/charger working, an electric drill and grinderette working for maybe two hours with no fault. I could not stop on the boat last night so disconnected everything except he Stirling. The boat’s 230v system was not connected. The only thing running was the Webasto diesel heater, programmed to come on at 3am.

I guess that was completely irresponsible of me because the marina went off at 3.30am this morning. Maybe when the Stirlings cooling fan came on?

Roumour has it that the new RCD is a type B and so will be tripped by stray DC currents which my charger may generate. Now this is quite beyond my skant knowledge of electrikery.

Do I now have to fit a new charger? Do I fit an isolation transformer?

Any advice will be cheerfully received.

Mike.

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1 minute ago, Alan de Enfield said:

If (say) 1 out of 100 boats causes the eleccy to trip I'd suggest that the fault lies with that 1 boat rather than a 'dicky marina set-up'.

Yeah but, no but, its only done it since they changed the supply innitt?

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5 minutes ago, mrsmelly said:

Yeah but, no but, its only done it since they changed the supply innitt?

So he should be thanking the marina for allowing him to find out he has electrical-worms escaping the boat.

At least he now knows about it and can do something before the hull falls to pieces (eggs-aggeration ?)

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We once had a previous boat on a slipway and connected to their supply, which kept tripping.

 

Initially I reckoned it wasn't our set up, because it worked fine back at base.

 

Then we discovered that because we were pointing heavily uphill, large amounts of water were cascading off the roof into the land-line connector, which despite being allegedly waterproof, was actually full of water.

 

Obviously if you are still afloat you haven't suddenly started sloping uphill, but, if you haven' already, it might be worth un-assembling any bits that might be able to get wet, and checking all inside is dry, and in good order.

 

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Good question.

When trying to reset the trip it would not reset, just flipped out again. They then isolated the jetties one at a time until it turned out to be my jetty, and so on to my pod. There are two boats on this pod, only mine was connected. QED.

But I have never managed to make it trip, only at 3.30am when I’m not there.

Mike.

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1 minute ago, BruceinSanity said:

If you’ve got odd DC currents wandering about, best answer is to fit an Airlink IT between the shore supply and your power inlet. Cost between £200 and £400, but still cheaper than overplating your hull...

The DC currents which trip class B RCCBs are generated maybe by motor speed controllers chopping the frequency or perhaps a smoothing condensor leaking to ground (look I am just reading from ‘tinterweb, I do not necessarily understand.)

Mike

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13 minutes ago, The Ents said:

Good question.

When trying to reset the trip it would not reset, just flipped out again. They then isolated the jetties one at a time until it turned out to be my jetty, and so on to my pod. There are two boats on this pod, only mine was connected. QED.

But I have never managed to make it trip, only at 3.30am when I’m not there.

Mike.

A correctly set up shore power system wouldn’t have RCDs in series - ie one master RCD and then numerous other RCDs (one at each bollard) feeding in to it.

 

Your bollard should have an RCD /RCBO on it. If your boat isn’t tripping your bollard’s RCD/RCBO, there is nothing wrong with your boat.

Edited by nicknorman
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2 minutes ago, nicknorman said:

A correctly set up shore power system wouldn’t have RCDs in series - ie one master RCD and then numerous other RCDs (one at each bollard) feeding in to it.

 

Your bollard should have an RCD on it. If your boat isn’t tripping your bollard’s RCD, there is nothing wrong with your boat.

Maybe the 'master' is a high sensitivity one and the individual RCDs are 'medium' sensitivity.

 

Possible ??

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3 minutes ago, nicknorman said:

A correctly set up shore power system wouldn’t have RCDs in series - ie one master RCD and then numerous other RCDs (one at each bollard) feeding in to it.

 

Your bollard should have an RCD on it. If your boat isn’t tripping your bollard’s RCD, there is nothing wrong with your boat.

On my Pod/Bollard there is a trip, I assumed it was just for current overload. Are there circuit breakers that do both residual current and overload?

Mike

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Just now, Alan de Enfield said:

Maybe the 'master' is a high sensitivity one and the individual RCDs are 'medium' sensitivity.

 

Possible ??

Possible, but it doesnt even have to be so. If there are numerous bollards each with the standard 30mA sensitivity, and each with an inevitable very small earth leakage current, feeding into one master RCD of the usual 30mA sensitivity, it is almost certain that the first thing to trip will be the master RCD. Which is bad, and why I say the whole installation seems to be badly designed.

1 minute ago, The Ents said:

On my Pod/Bollard there is a trip, I assumed it was just for current overload. Are there circuit breakers that do both residual current and overload?

Mike

Yes, that is what an RCBO is.

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2 minutes ago, Alan de Enfield said:

Maybe the 'master' is a high sensitivity one and the individual RCDs are 'medium' sensitivity.

 

Possible ??

Yes, I believe the RCD on the jetty, each jetty has its own RCD as well, is class A and 30ma, the one for the main marina is class B and rated at 10ma.

Mike.

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I had a Sterling charger which, when working hard, sent a large amount of ac down the battery negative output (not the mains earth) which was of course connected to the hull and hence the mains earth - in fact I blame it for the otherwise unexplained dissolving away of my hull. It would trip an RCD but only when working hard. I have thrown it in a skip! So I wonder, did the charger cut in at 3.30?

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2 minutes ago, nicknorman said:

Possible, but it doesnt even have to be so. If there are numerous bollards each with the standard 30mA sensitivity, and each with an inevitable very small earth leakage current, feeding into one master RCD of the usual 30mA sensitivity, it is almost certain that the first thing to trip will be the master RCD. Which is bad, and why I say the whole installation seems to be badly designed.

Yes, that is what an RCBO is.

Ah. Forgive my ignorance.

Mike

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5 minutes ago, The Ents said:

one for the main marina is class B and rated at 10ma

That is very low - a typical 30Ma MUST blow by 30ma, and most blow around 23ma, I guess that the 10ma would blow at about 7 or 8 ma. - almost nothing.

 

It is cumulative so all the other boats are not quite taking it over the edge but when your 'comes on line' it goes over the top.

 

See if you can get the marina to try with everybody disconnected and then re-connect you, then one by one all the others, it could well be the 'last one; pushes it over the edge,.(whoever the last one is)

 

Alternatively get them to swap it over for a 30ma and see if it still pops the whole system.

Edited by Alan de Enfield
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8 minutes ago, nicknorman said:

Possible, but it doesnt even have to be so. If there are numerous bollards each with the standard 30mA sensitivity, and each with an inevitable very small earth leakage current, feeding into one master RCD of the usual 30mA sensitivity, it is almost certain that the first thing to trip will be the master RCD. Which is bad, and why I say the whole installation seems to be badly designed.

 

exactly.  

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