Tom

First day in static caravan... electric tripping, help!

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Moved in to the static yesterday. Cosmic.

All going well, or at least as well as can be expected. Today electrics fine, but then suddenly this afternoon the rcd trips and won't go back "on". I turn off the three switches in the consumer unit: lights, ring main and heaters. I can turn the rcd back to on, but if I turn any of the three switches to "on" it trips again. I'm guessing there can't be a downstream fault in the three circuits as any of them trips it, so there must be a fault upstream in the supply to the consumer unit - is that right? Help!!

At the moment sat here with an extension lead from the barn powering our router and a light... 

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Most likely one of the circuits has a neutral to earth fault so any of them drawing any current trips it.

 

Unless you have some test equipment and have some knowledge you need an electrician to do some testing.

 

If you want to narrow it down further and feel competent I can suggest some things to try.

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Turn RCD on first

then each mcb one at a time. 
does that change anything?

 

 

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Oh and make sure all appliances are switched off and lights off

 

as you switch anything on watch for power going off invade this helps prove part of circuit/appliance causing issue

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1 minute ago, TonyT said:

Oh and make sure all appliances are switched off and lights off

 

as you switch anything on watch for power going off invade this helps prove part of circuit/appliance causing issue

All appliances and lights off. I turn on the RCD and can switch on all 3 mcb's - but drawing any current on any of the 3 mcb controlled circuits- e.g. turning a light or any appliance on, trips it.

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5 minutes ago, ProDave said:

Most likely one of the circuits has a neutral to earth fault so any of them drawing any current trips it.

 

Unless you have some test equipment and have some knowledge you need an electrician to do some testing.

 

If you want to narrow it down further and feel competent I can suggest some things to try.

 

Yes please Dave!

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2 minutes ago, Tom said:

 

Yes please Dave!

Right, open up your consumer unit.  If it follows the norm for these things there will be an RCD main switch and 3 mcb's.

 

Disconnect the L AND the N from one of the circuits try resetting the RCD and see if the remaining 2 circuits works and does not trip the RCD.

 

If it still trips re connect that one and dosconnect both L and N of the next circuit and try it.

 

Hopefully you will result in 2 of the circuits connected and working and the fault will be on the third disconnected circuit.

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Pic attached, remove wires going in to the top of the mcb?

20210220_190356.jpg

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One circuit at a time, remove the wires from the MCB AND remove the corresponding neutral wired from the neutral block top left.  Take particular care to follow the lives back to identify the cable and identify the corresponding neutral.  Neutrals look all jumbled up in the N block so not as straightforward as it could be.

 

the first mcb, the 32A one, looks to be a red / black ring final with a later brown / blue spur added.  Treat that as 2 circuits so try removing the 2 reds (and corresponding blacks) or try removing the brown and corresponding blue one at a time.

 

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Thanks Dave and thanks Tony - great video. So I've tried removing each wire from each mcb in turn, and their corresponding neutral (and earth, though rereading your post Dave it looks like I needn't have bothered, makes sense when I think about it). Anyway, makes no difference, the RCD keeps tripping when I turn an appliance on, heater on or flip the lighting mcb (guess there must be a slight load on this circuit).

A lot of the time the RCD doesn't reset even if all mcb's are in the off position. It takes multiple attempts and then it will finally stay on.

Faulty RCD? 

20210220_190356.jpg

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Sounds reasonable that the whole RCD is faulty if it’s not holding in after all that fault diagnosis 

 

don’t know what spares are like for a like for like replacement RCD ,  may be cheaper to replace the whole board £ 30 -£40 at screwfix.

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Either some damp in it or a faulty box mate.

 

Either way a new breaker is in order - had the same issue on my site last week - the power kept tripping (we bunged next door £500 for the temp feed) and had the sparks out - his breaker was full of water.  Ooops.

 

All good now though - need my tea at 7am!!

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This is where you really need the full kit of test equipment, at least insulation test and RCD test.

 

You could try replacing the RCD if notI suspect you need an electrician.

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So pondering this while lying awake at 3am last night: if I AM able to switch the RCD to the on position (even after a few tries) then it cant be a neutral/earth fault? As irrespective of the MCD position it should trip straight away - is that right? It seems to trip when there is load on any of the circuits - a neutral/earth fault should trip the RCD irrespective of whether there is load on a circuit or not. So it MUST be a faulty RCD?

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A high resistance on neutral might do it (as there's always *some* leakage current to earth) but it does sound like it's the RCD.

 

but whenever you *do* get the RCD to latch in and the lighting MCB trips it that does allude to a problem with that circuit. Is there an extractor fan in the loo perhaps?

 

Where is the power coming from for the van? What kind of cable? Is there an earth rod?

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A neutral - earth fault will result in some of the return current from any load travelling via earth, not neutral so it creates an imbalance between L and N and the RCD does it's job of tripping.

 

So there will only be a return current and hence an imbalance when a load is turned on.

 

No loads (all mcb's off) = no current flowing = no imbalance = no rcd trip.

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The lighting MCB trips it when I switch it to on true, but I can switch the other two MCBs on but then any load on those trips it too. So can it be a fault on any one circuit?

No extractor fan in the loo (unfortunately). There is no earth rod for the van itself, but the supply is from one of the barns via the 3phase supply to these - it's a 16a cable. I've already tried replacing this as I was initially thinking it must have been a fault on the supply.

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Any chance  N and E are reversed at the source?

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Are all your connections tight? Particularly the neutrals both at the source (where it's fed from), in the cu and at any junctions along the way.

 

You haven't had any digging done that may have caught the supply cable or if overhead the same, or any serious chaffing? 

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Was working fine, but then went.

No digging and no chaffing. Would a supply fault to the caravan cause the RCD to trip though? The RCD in the barn from which it is connected is not tripping.

Just having a look now at the board thinking I might go through it and test again, but cannot now switch the RCD on at all. All MCBs off. 

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22 minutes ago, Tom said:

The RCD in the barn from which it is connected is not tripping.

I am not an electrician! but was wondering how it is all earthed.

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one more... do I need to replace the rcd like for like or are they a generic fitment and I can just get the same ampage? 

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Just now, PeterStarck said:

I am not an electrician! but was wondering how it is all earthed.

The caravan is effectively a spur from the barn. 

 

Just thinking: is there any point measuring the resistance between the neutral and earth rails in the box? Presume should be high unless there is a fault?

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