Help required with a Domestic Ring Final fault

[claret73]

Evening Chaps...
Had a 2nd call out today to a relative (let's say they're a client) for a fault on the downstairs Sockets.

In a nutshell the downstairs sockets are tripping the RCD. Been there nearly all day & cannot fathom out what might be the cause?

So, the board is a 16th MCB Only. There is a 63A 30mA RCD between the meter & the Main Switch which protects all circuits. It is only the downstairs sockets tripping the RCD. The circuit concerned is 2x Rings into the MCB. 1 does 3x sockets in the front room, the 2nd does the dining room, kitchen & outside socket which runs out an armoured to a 2nd weatherproof box.

I disconnected the outside socket from the spurred cable in the dining room. Switched back on, still trips. Split out the circuits having done a continuity to find the 2x legs. Found out which was the tripping circuit & ignored the other. All Appliances were disconnected.

Tests I performed:
End to end to check continuity on Line & CPC
Line to CPC Insulation resistance
Ramp Test on the RCD

The board is boxed into a corner & the Neutral bar is very difficult to get access to, so was not too happy with taking out the Neutral connections.
However I reconnected the circuit & did L-CPC, N-CPC & L-N Insulation resistance.

The meter read >99.9 (Megger MFT) & so all Cables were deemed OK?
Took all sockets concerend off & checked for nicks/damage & tightness of the terminals. All OK...

So I don't know what the problem is? It's still tripping. I put the other Ring back in to give them some power.

Any ideas what I may have glaringly missed??? Any help greatly appreciated...
Thanks
Andy

 

[Octopus]

I'd split the ring in two and connect one half to the board to see what happens, then do the same with the other "side". Hopefully doing this will offer you some clues, then you can focus on the exact cables.

By any chance do they have any rodent damage?

 

[paturback]

Are you saying you got two rings in 1 mcb?

 

[claret73]

Murdoch, that's what I have done. I found which 2 cables made the ring for each ring & put them back into the board. 1 trips out the other is fine. But the one tripping tests out ok on IR...

Paturback. Yep! 2 separate Rings in 1 MCB, ie. 4 Line cables into a 32A MCB. I have split these out to fathom out which 2 cables belong to that particular ring. It deffo is a ring in each case as get end to end continuity...

Rodent damage? I can't see anything or came across any signs of chewed cables/Mice droppings etc. The tripping is intermittent. I was there 2 weeks ago & the following day another Spark reconnected the problem ring & has been working since until yesterday where it tripped again & now cannot be reinstated as it doesn't hold.

 

[claret73]

Murdoch
Got your reply crossed there...I see what you mean. But I don't know where the first feed or last feed is? It's looking a Bitch! The circuit for the dining & Kitchen are fed up & over then down as they have a concrete floor in the dining room. (The board is in the front room of the house). I haven't gone as far as trying to bell out where my first feed/socket is. If the cables run under the bathroom floor I'm screwed as they have a tiled floor.

 

[BillyTheSparks]

If its just the rcd tripping, that would lead me to suspect a N-E fault not a L-E fault. Going by what you have said, you have really only tested IR L-E this will show clear as there is no fault. I would assume that if you did the IR N-E you would have something to find.

If you just split the ring circuit at any socket, you can then test one 'Leg' of the ring assuming that you have again dissconected the legs at the C/U also. And hopefully keep doing this until you find the 'Leg' between two sockets which is causing the grief. ( be careful that you dont get all flustered when doing this; you can get in a right Tis!!)

 

[Des 56]

Have you done an insulation resistance test of all the circuits

One possibility.a neutral earth fault on a lightly loaded circuit,ie lights, and the rcd stays put
Apply a heavier load on a socket on the ring and the load is enough to imbalance the rcd and out she goes

 

[claret73]

Billy
I have done L-E with the cables out of the board. I did reconnect the tripping ring into the breaker & earth bar & then did N-E, N-L (At Terminal of Breaker) & L-E. All tested perfect. (But am I doing something wrong there?
Yeah... it's coming down to breaking it down...

Des
No I haven't done that. That will be worth doing. He did say that a bedroom light doesn't work...which did make me think, but by that point I was all over the shop on a one way street...

Thanks for all the help so far Guys! Much appreciated. Just so frustrating!!! He's a relative so not entirely valid, but if this was a client how would you determine payment terms from the off & then if you can't find/fix it how do you consider charging for that time?

 

[BillyTheSparks]

Billy
I have done L-E with the cables out of the board. I did reconnect the tripping ring into the breaker & earth bar & then did N-E, N-L (At Terminal of Breaker) & L-E. All tested perfect. (But am I doing something wrong there?
Yeah... it's coming down to breaking it down...QUOTE]

Ah Diddnt understand first time around.

Are there any outside lights which are on that circuit either via a FCU or straight from a JB somewhere (or even from the back of a socket!!)?

 

[Newsome3]

Bear of luck with your fault finding
Let us know how you get on and what fault was once found

 

[claret73]

Billy
There is a PIR Halogen off a Switched FCU...but this was switched off during the test...I did have a look inside & found a choc block...The load cable was too short!!! (How can you do that????) It is a Mess!!! The whole lot! I'll be doing my best to sort out the fault, but I'm staying clear of any installation work he might have in the future. House smacks of previous owners DIY Antics!!!

 

[WayneL]

Hi Claret73,

A couple of questions:


1 Does the RCD trip under any circumstances - or only under load....i.e. something plugged in and switched on?

2 How are you certain that it is a fault on one of the Ring Finals that is causing the tripping? How did you establish this?

If it only trips under load, you need to do a N - E IR test on each circuit (neutrals disconnected, I'm afraid), as the chances are you have a N-E fault on one of the circuits.
It could be any of the circuits carrying the fault, even if it's a load on the Ring Final that's causing the tripping.

If it's tripping without a load (as soon as you turn the MCB on, then chances are you have a L - E fault on that circuit - but that would have been obvious with the testing you've already done.

Keep us updated.

 

[kung]

Have you done an insulation resistance test of all the circuits

One possibility.a neutral earth fault on a lightly loaded circuit,ie lights, and the rcd stays put
Apply a heavier load on a socket on the ring and the load is enough to imbalance the rcd and out she goes

Got to admit id do the same at this stage and link L/N + E and test board as a whole ! might be supprised what you find !

 

[claret73]

Thanks for all the info Lads!

Wayne, the Circuit does trip with all loads removed but I do still have the Neutrals connected...I did L-E IR with the Line & CPC legs disconnected & I'm getting perfect IR? I'm going to have to bite the bullet & take the Neutrals out! Maybe start breaking the board down and testing each circuit. Guess I'd got one track minded & spent too much time on the ring without consideration of the other circuits. I'll get some Pics of the board then you'll all see why I left them in...

 

[Octopus]

Unless you take the neutrals out and do the IR's on them you'll not track the fault down IMHO.

 

[topquark]

Do you have a clamp meter at your disposal? If so I'd be tempted to try and confirm your suspicion about the RFC using that (and eliminate the other circuits as well if possible). As the RCD is before all of the circuits you are probably dealing with a combination of leakage faults. You have a ramp test from the RCD so you'll know what it's tripping threashold is.

 

[truckster]

Gotta get them neutrals out.

 

[claret73]

Thanks again Lads! Going back on Friday...Not got a clamp meter to hand...(Ahem!)
Got a call today to go look at another fault job, tripping MCB on a lighting circuit!! Ohhhh Nooooo! It's really not my forté...

 

[topquark]

Faults like these will become more and more prevalent, anyone local to you that could lend you one?

 

[Big n Daft]

It sounds to me like a nuetral. I'd IR test the whole shooting match at the DB then disconnect that outside pir/light thingy. If that doesnt sort it then its testing all the circuits in a methodical manner at the DB.
Best of luck.