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

 

[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

 

[Brooks-Electric]

I would suggest neutral on the faulty leg is interconnected with a neutral of another circuit (likely to be cooker). I am assuming you only removed the circuit in question to carryout the testing. Therefore leakage back through other neutral to earth at transformer. I would suggest removing faulty neutral and carrying out test between that and the neutrals of the other circuits on that RCD.

 

[Rauer]

Does it the circuit trip under load?

 

[1shortcircuit]

I would suggest neutral on the faulty leg is interconnected with a neutral of another circuit (likely to be cooker). I am assuming you only removed the circuit in question to carryout the testing. Therefore leakage back through other neutral to earth at transformer. I would suggest removing faulty neutral and carrying out test between that and the neutrals of the other circuits on that RCD.

I've tested for borrowed Neutrals between other circuits as this is what I first suspected. Also, whilst the circuit was removed I tested for continuity of both Neutral legs to the main earth bar of consumer unit and nothing :thumbsup

Does it the circuit trip under load?

Nope, not a single trip and circuit has been under normal daily usage

Thanks for all your help everyone, much appreciated as always.

 

[Rauer]

Start splitting it down to find it!!

 

[Des 56]

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.

The thread title is "bizarre dead short"we will have to call you 2shortcircuit from now on
Your reading has only confirmed that you dont have a million ohms,add a bit of resistance of the cpc back to the met and its not that bizarre I would say for the rcd to hang on in there

 

[Jimmy Boy]

That will be fine just write down for 'Design ' Electrical Trainee and Signed of by NICEIC supervisor ..Of course I am being flippant..? ' Tony Cable'..my autobiography I woke after 5 weeks from a coma...To find myself as an Electrician lol

 

[1shortcircuit]

Start splitting it down to find it!!

Read the first line of my opening post lol

 

[1shortcircuit]

The thread title is "bizarre dead short"we will have to call you 2shortcircuit from now on
Your reading has only confirmed that you dont have a million ohms,add a bit of resistance of the cpc back to the met and its not that bizarre I would say for the rcd to hang on in there

It would seem you have hit the nail on the head.

The earth leakage is obviously working within the tolerance of the 30mA RCD therefore not tripping it however at a later date this could become worse and lead to nuisance tripping or the amount of leakage combined with that of other circuits could eventually step out of the tolerance level again causing nuisance tripping.

At least my actions of finding and rectifying the fault were correct and should eliminate any tripping of the device.

**** note to myself, Learn more, test more and understand more ****


Thanks again to everyone that has added their input, great forum.... I continue to learn more everytime I log on:thumbsup