Short circuit tripping RCD

Dancook

Distinguished Member
why dont you just remove the fuse from the fused spur before you try disconnecting the N and E and then monitor the behaviour of the mcb marked downstairs ring that keeps tripping........i would try this first.

Removed fuses, turned on MCB, tripped 15 minutes later

Is the RCD tripping..

Both MCB for ground floor circuit and RCD trip yes

Then unless its ancient, the switch will be double pole. The back of the faceplate should indicate that. So switching it off, will isolate the electric ufh from your RCD.

Oh it's been switched off for a couple of years, and i did just remove the fuses and test but 15 minutes later the MCB/RCD both tripped. So maybe it's not the UFH at all.

A N/E fault cannot possibly trip the MCB.

An earth fault can cause a dead short

Conflicting information ?
 

ufo550

Well-known Member
Hang on a minute... MCB -and- RCD are tripping. This can only be a problem with the live side of things. A N/E fault cannot possibly trip the MCB.

So single pole isolators / removing fuses is a totally reliable means of isolating this issue.

I suspect you have a hidden junction box somewhere you don't know about that is full of water.

This really is a job for a professional.
Not being funny, but a neutral conductor is a live conductor. If it’s accidentally connected to earth, the current will flow through the live line conductor, through the neutral live conductor, and then partially to earth. So it will trip both RCD and mcb, proportionately to the resistance in each. Dependant on the fault, it will be a race between the two.

However I agree, OP should employ a competent electrician.
 

Dancook

Distinguished Member
I found one last appliance that was still plugged in.. i will try one last time and give electrician a call in the morning

he was meant to call me this morning, but i guess he got side tracked with work.

123629348_10164706805755227_6101602255991421642_n.jpg

The kitchen electrics aren't looking particularly safe .. but I don't run the hob and the dishwasher at the same time.

123658276_1007511933005857_9165840661489879085_n.jpg
 

stevelup

Distinguished Member
Not being funny, but a neutral conductor is a live conductor. If it’s accidentally connected to earth, the current will flow through the live line conductor, through the neutral live conductor, and then partially to earth. So it will trip both RCD and mcb, proportionately to the resistance in each. Dependant on the fault, it will be a race between the two.

However I agree, OP should employ a competent electrician.

I disagree.

The OP has either disconnected or turned off everything on the affected circuit yet the MCB is still tripping. With everything turned off or disconnected, that live feed out of the consumer unit is literally connected to nothing. Nothing at all you could do to neutral or earth would cause any current to flow down the live conductor.

The fault has to be on the live conductor. Either somewhere in hidden infrastructure, or something has been missed during the 'isolating' session.
 

Aerojon

Active Member
Sound like water ingress somewhere,causing an imbalance which is why the RCD is tripping..

or live to earth fault..
 

ufo550

Well-known Member
I disagree.

The OP has either disconnected or turned off everything on the affected circuit yet the MCB is still tripping. With everything turned off or disconnected, that live feed out of the consumer unit is literally connected to nothing. Nothing at all you could do to neutral or earth would cause any current to flow down the live conductor.

The fault has to be on the live conductor. Either somewhere in hidden infrastructure, or something has been missed during the 'isolating' session.

As said a neutral conductor is a live conductor, it carries current. In this instance there could well be a fault live to earth. But the fault could also be between neutral to earth, that could also trip both the RCD and mcb, as could a live to earth fault.

The fault could be in the fixed wiring, replicated by mechanical pressure, a pinched cable under floorboards for example. It could be a fault within an appliance, that has not be disconnected, and which is only replicated when the appliance cycles, for example a fridge or freezer.

I‘ve come across various faults in my time.
Examples; a strapper cable between two way lighting, one wire in the cable had been nailed into. The fault was only discovered, when the adjacent bathroom was being refurbished and the plumber was getting shocks off the wall when touch copper pipes. Fault finder was also complicated by the position of two way lighting switches.

Another was a pinched neutral cable on a rarely used landing socket. Only replicated, when a high load appliance was plugged into the socket.

Another, where a diy’er had installed a smoke alarm, and had connected the cpc into the interconnect. The RCD failed to function under test.

My point is, we can go round the houses, pontificating the problem. In this case the OP has tried the obvious. He now needs to leave it with a competent electrician, with suitable experience and test equipment, who should carry out test procedures as outlined in BS7671.
 

logonuser1

Active Member
Do you own a ammeter?

Also you have not recently rewired a plug or anything as this can also be caused by the incorect polatity ,ie the Nin the L and the L in the N on a 13amp plug
 
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Dancook

Distinguished Member

On Thursday morning I'd tested removing the fuse from the UFH but it still tripped.

This morning the electrician came out to disconnect the UFH completely, says taking out the fuse only affects the live and doesn't stop a current travelling the neutral wire and tripping the circuit - i think that's what he said anyway.. :D

Anyway since he did that this morning around 9:30am it has not tripped since...

I wanted to give it at least 24 hours before I gave it the all clear :)


There is always the possibility there was something wet which has finally dried out.. but we will see.
 

Aerojon

Active Member
Unless you know for certain the fused spur is double poled,removing fuse same as switching off will only isolate live..
At least there's progress,fact that water/damp is ingressing into the UFH circuitry is a bit disconcerting..
 

Dancook

Distinguished Member
Unless you know for certain the fused spur is double poled,removing fuse same as switching off will only isolate live..
At least there's progress,fact that water/damp is ingressing into the UFH circuitry is a bit disconcerting..

Does the UFH tripping somehow prove water ingress then? it can't have happened for another reason?

We're not in a financial position to fix the UFH anyway, it's been turned off for a couple of years, maybe after covid and when I'm earning again I'll get it all fixed.
 

its_all_Greek

Distinguished Member
It doesn't prove water ingress, it just means there is some form of breakdown in the underfloor heating.

I've never installed it but would imagine its the type of stuff that isn't easily repaired from an access point of view, A reputable company who does this sort of thing should be able to identify where in the system the fault is and then only access under the floor covering there meaning only minimal damage if any, but i suspect that they will only be able to identify the first fault with the underfloor heating its possible that there could be more than one and then obviously the costs would increase.
 

IronGiant

Moderator
Is this a wet system or electrically heated grids?
 

logonuser1

Active Member
Just disconect the load side of the fused spur, tape up the wires going to the ufh, replaces the cover of fused spur and forget about the heating in bathroom then.
 

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