Nuisance tripping after splitting a ring main

[Mfctitch]

Evening everyone

Had to re post as I started a post within a post

here's hoping I'm posting in the right part or I have started off on the wrong foot.
Long story
Asked by a friend to look at his friends electrics as the kitchen ring was tripping the RCD.
New colours cable
on 32amp B MCB
one of only 3 on the this bank protected by an RCD
5 double sockets
plus a bank of 6 FCU's

Before I went there I had him remove all the plugs plus and turn off the FCU's
believing that this would help narrow down the problem.
But it did not.
so drove to Leytonstone about 45 mins from me
where we split the ring at a double socket and we believed that we had found a the problem which was a bit of cable in the wall between one of the FCU's and a socket in the cupboard.
all this time the other leg was working fine.
So we managed to replace the cable and we seemed to be on the home stretch, when the other leg started to trip I been there for about 5 hours and it was 9pm by now so turned the ring into a radial thinking this will do until I get time to investigate further.
so left at 10:30pm and everything seemed fine only to get a call today saying that the MCB had tripped but not the RCD and thoughts apart from run.

 

[Octopus]

is it because of my experience at fault finding or the fact that no one on here can come up with a step by step suggestion that would solve the issue.
other than get someone in who could solve the problem yet not explaine how to solve the problem if that makes sense

You refer to solving a problem, yet you have not identified the problem(s) as yet, despite suggestions on here

Maybe you should reconsider Tony ‘s offer to assist you ......

Fault finding effectively takes many years of experience .....something you can’t pick up from the internet.

As for basics, you never answered my question about the end to end readings so how do you know you have a continuous ring across the 3 cores ?

Your approach can be best described as haphazard and I trust you are not charging by the hour ......

 

[Jon Bateson]

Really is a simple task to find a fault that is actually measured and present. Loads. Of people have given you correct advice. Try plumbing it may suit better

 

[mhar]

Attached is a scan of a map of a circuit I drew out. None of my initial readings pointed me towards what was going on but socket Zs readings were not as I would expect from an rfc (plus a few other things ringing alarm bells). Splitting the 'ring' at various points also produced some unexpected results so I disconnected every accessory on the circuit, joined r1 to r2 on one leg of the 'ring' at the db and went round every point to see where I had continuity. It started ok as I had a reading of 0.27 Ohms on dining room 3, however when I connected the single outgoing set of conductors I had continuity on Lounge 3 and dining 4 so a concealed junction with lounge 3 being a spur. Dining 5 and lounge 4 when (single) outgoing conductors were connected revealed further concealed junctions feeding spurs. Dining 2 revealed a concealed jb with a spur from a spur. Lounge 5 revealed the end of the 'ring', a concealed spur to annexe 2 and a spur to lounge 6 which in turn fed two spurs plus another spur feeding a spur. Basically I had multiple concealed interconnects and multiple concealed spurs.
First thing is all this was discovered before doing a board change during my pre board change testing.
If I had an ir (tripping) problem I would have done exactly the same but would have ir tested the whole circuit each time I introduced (reconnected) an accessory.
Not every instance can be answered on an internet forum. A methodical approach is what is required together with a visualisation of what you are dealing with. You have actually been given a lot of very good advice based on experience, sometimes though you really do have to go right back to basics.

 

[Mark42]

I had a similar scenario at a mate's house last month: he'd been changing switches, and got intermediates, two-ways and singles completely messed up, and had mixed up two separate multi-way lighting circuits in the same enclosures. Nothing made sense: the behavior of his lighting was hilarious.
With multiple concurrent faults there's sometimes too much going on to hold the logic in your head.

In that case I find the best way is to STOP. To give up trying to be clever and to disconnect EVERYTHING. All accessories off, all cables neatly disconnected. Then get pen and paper, a long flying lead and trace the exact route of every cable. Draw it as you go. Then do continuity and IR on all sections, logically and consistently.

It's then a great feeling when the 'A-Ha!' point is reached, which it will be.
Good luck

Ref my post #73, repeated above.

As others have said again and again, I think you really do need to take everything apart.

The mate in my above post who couldn't figure out his lighting is a retired Naval Commander, and currently a bloody airline pilot. But he couldn't figure out some simple wiring. Fault-finding can be confusing: sometimes it's difficult to see what is staring you in the face. It's never anything to be embarrassed about, and a second pair of eyes is always useful.

 

[Andrew Hunter]

Hi - with an mcb now tripping I’m placing a bitcoin bet on a trapped L behind one of the faceplates .

No sorry forget this peice of info! RCD would still trip if it was a live or phase conductor as well as the MCB. You are correct that if it is a Phase conductor on the out going/load side of a FCU this would only show when switched but would still trip the RCD.
No I think there is possibly an overload issue going on when all the FCUs are on and all the plugs in and switched on which depending on where the devide in the circuit that you split is could potentially have a fire risk.
So as Charlie said. you need to go back and return the ring back to the original state (with new link where fault found) and then break the circuit down and conduct complete rimg main test then start breaking it down to identify exactly where the fault is. Out of curiosity did you ask the first question every spark should ask when attendind a sudden unexplainable fault "What/Where have you/someone/anyone been doing recently DIY/work wise"
most of the time this narrows it down to the offending culprit.

 

[Mfctitch]

Hello everyone
Really sorry for taking so long to get back to the forum after receiving so many replies. Work got in the way and now on holiday.
But upshot of the problem turned out to be two fold on first leg we pulled some cable up through the floor and found a small hole in the outer sheathing not a bite mark and no nails in sight so cut this out and replaced with a small section..
We are still running the kitchen as a radial as the other leg is impossible to get at without taking the floor up which the customer does not want to do and although I'm a small bloke even I cannot get under the joists..
We have suggested running the leg along the outside wall and back into the cellar at a later stage if he wants.

So basically this is just a thank you for all of your help when really all that was needed was some time, patience and some logical thinking

 

[telectrix]

tell customer that the floor ( or part of it) needs to come up to locate the fault and maybe replace the faulty section. other wise he can call a magician.

 

[Pete999]

Hello everyone
Really sorry for taking so long to get back to the forum after receiving so many replies. Work got in the way and now on holiday.
But upshot of the problem turned out to be two fold on first leg we pulled some cable up through the floor and found a small hole in the outer sheathing not a bite mark and no nails in sight so cut this out and replaced with a small section..
We are still running the kitchen as a radial as the other leg is impossible to get at without taking the floor up which the customer does not want to do and although I'm a small bloke even I cannot get under the joists..
We have suggested running the leg along the outside wall and back into the cellar at a later stage if he wants.

So basically this is just a thank you for all of your help when really all that was needed was some time, patience and some logical thinking

Hello everyone
Really sorry for taking so long to get back to the forum after receiving so many replies. Work got in the way and now on holiday.
But upshot of the problem turned out to be two fold on first leg we pulled some cable up through the floor and found a small hole in the outer sheathing not a bite mark and no nails in sight so cut this out and replaced with a small section..
We are still running the kitchen as a radial as the other leg is impossible to get at without taking the floor up which the customer does not want to do and although I'm a small bloke even I cannot get under the joists..
We have suggested running the leg along the outside wall and back into the cellar at a later stage if he wants.

So basically this is just a thank you for all of your help when really all that was needed was some time, patience and some logical thinking

What is tripping?

 

[telectrix]

What is tripping?

tripping is something we did back when L.S.D. was all the rage. .

 

[Pete999]

tripping is something we did back when L.S.D. was all the rage. .

Showing your age now Mate, oh sorry all age related stuff is in the mind, mind you my mind is fuddled with all that tripping and it wern't an OCPD tripping either!!!!!!!!!?????/ Did a great deal of tripping in my later years at work Russia, the US, Canada, far and middle East need I go on? did my head in I can tell you, the gatt was a revalation though, grew in the hedgsrows of Sanna