Bizarre dead short between Neutral and Earth

[1shortcircuit]

Firstly, please let me explain the fault on the circuit HAS been rectified. This was achieved by splitting the offending circuit (kitchen ring) into two radials and putting each leg on their own 16A mcb on the same RCD.

Attended a property to do some remedial works on the kitchen ring, New dual RCD protected board already installed and just there to put rubber grommets into back boxes. Such a joy:tongue3:

Anyway as I always test circuits before working on them I found a dead short between Neutral and Earth but RCD holds?

RCD tests came back well within specified tripping times on x1 and x5 tests but RCD failed to recognise this dead short?

Anyone have any suggestions as to why this RCD will test fine but not do it's job as intended?

All testing was done with circuit completely removed from Consumer Unit. Faulty leg found between two sockets so removed and as said made ring into two radials, each on their own mcb (same RCD). Comment sticker left on consumer unit explaining circuits 2 & 3 both energise kicthen.

Kind Regards

1SC

 

[Richard Burns]

cpc not connected back to the CU correctly?

 

[1shortcircuit]

cpc not connected back to the CU correctly?

All connections terminated correctly and securely:thumbsup

 

[Chr!s]

What resistance was this dead short?

What Earthing system?

 

[1shortcircuit]

What resistance was this dead short?

What Earthing system?

Resistance 0.00 Meg

Earthing, TNS

 

[DPG]

Definately zero ohms, ie. on a low ohms range?? Daz

 

[Chr!s]

Resistance 0.00 Meg

Earthing, TNS

So the resistance could be as high as 9999 ohm's?

 

[1shortcircuit]

So the resistance could be as high as 9999 ohm's?

Erm, quite possibly?

So whilst the IR reading was low enough to require further investigation and rectification there may have been enough resistance between Neutral and Earth to not trip the RCD.

 

[DPG]

I'd measure on a low ohms range and get a figure in ohms rather than megohms. Daz

 

[1shortcircuit]

I'd measure on a low ohms range and get a figure in ohms rather than megohms. Daz

I think you are right.

 

[telectrix]

and then look for the nail.

 

[oldtimer]

Also take a link of cable and short neutral and earth at the CU just to confirm then say the cooker circuit is on the same RCD then get your r1 r2 test plug at at the cooker outlet short out N-E

 

[1shortcircuit]

and then look for the nail.

Well it seems the kitchen cabinets MAY have been screwed to the wall and from what I can tell the cabling has not followed safe zones so it could have been a screw I guess??? Could be here all day guessing which is why I just cut out the faulty link and created two radials

Also take a link of cable and short neutral and earth at the CU just to confirm then say the cooker circuit is on the same RCD then get your r1 r2 test plug at at the cooker outlet short out N-E

I was wondering this myself, Just to prove that in the event there is a fault the RCD does actually do what it's supposed to do.

I did contact Elecsa, who I must add have been excellent on the two occasions that I have needed to contact them and even they said it doesn't make sense.

Thanks for everyone's input:thumbsup

 

[nickblake]

Ah ha i bet its a nail like tel has said had one simular all readings were ok RCD tripping time hunky dory , with the circuits operating all fine then RCD would trip for no reason drove me mad trying to find it new RCD's etc as you do tested circuit all clear then the RCD would trip , located the fault to a capping nail that was straight through the cable it was intermittantly shorting and tripping the RCD pig to find so it could well be an intermittant short

 

[1shortcircuit]

This circuit has not created any nuisance tripping since the board has been replaced and the property has been in full use :thumbsup

 

[needasparks]

Be good to know what make board this is on.

 

[oldtimer]

The thing is what lessons should be taken from this well yep you have a low reading but at the same time it costs nothing to do some other tests as well even if you just jott them down a bit like a British Gas guy who tests a socket and says big problem here you have no earth but if he tested some other sockets ie random he may have said this socket has no earth but the others are ok

 

[vernam616]

try it on another RCD and see if it holds

RCD may be faulty, maybe you got decent trip times but doesnt mean it cannot be faulty

 

[1shortcircuit]

RCD may be faulty, maybe you got decent trip times but doesnt mean it cannot be faulty

Kind of defeats the object of carrying out the correct tests in sequence though wouldn't you agree?

 

[vernam616]

Yes i suppose it does im not disagreeing with you, however that would be my first try, lets face it what could cause the RCD NOT to trip? when we all know it should be