RCBO tripping mystery

This sounds very odd - this may be an installation with some N-E fault or N-N fault between the circuits. With no neutral connection to the RCBO, there is no source of power for the internal detectors, so it will never trip - that is not a proper test, or a safe state to leave it in.


 As an aside also if you repost this to the electrical part of the site, (the wiring & regs forum) it will get read by more folk who may be better placed to answer it than I am.

Mike.

My guess is a "Borrowed Neutral" on the lighting circuit - not uncommon to find this bodge especially stairs/landing where it's not clear on a feed or 2 way switch if the circuit belongs upstairs or downstairs and which neutral is which...


I agree with Mike above - you shouldn't leave it like this for some other poor soul to come across, and I predict a significant amount of investigation of the various circuits to separate out each set of neutrals. I'll also bet that the householder is upset because "it just works at the moment". That is until someone gets a belt off a horrid not to UK standard light fitting bought from China off eBay (there are other offenders too) and the RCBO can't trip to save their life.

Moved to the Wiring Regs category.

who disconnected and taped the neutral fly leads and why?


If the " why" is a fault, then the fault needs to be fixed.

Long RCBO neutral lead would not be the cause of the problem. You first have to check the RCBO with the circuit disconnected and then installation test the circuits if clear check the lighting and alarm neutrals are separate. It’s quite possible to have faulty RCBOs but is sounds to me like a diyer at work or mice. Highly unlikely for two RCBOs to just start tripping and who disconnected the neutrals?

If you don't have access and customer won't let you fix problem issue an electrical danger notice form to cover your backside.



Gary

To reinforce other comments here:

1) Mere excessive length should be no issue unless inductive effects are messing with a hypersensitive RCD.

The neutral lead (and the cream reference earth if your device has one) of an RCBO *should* be cut to an appropriate length (Schneider instructs you to do so, possibly other manufacturers, I haven't read all the mfr installation guides in a while) which, depending on circumstances, may be long enough to reach the furthest part of the DB (allowing the device to be relocated when it is re-tasked in future alterations) but at any rate *should not* have 3 or 5 loops of slack cable-tied and stuffed behind the other wires to make inductor-like interference in the other circuits.  (I've never understood why Schneider make their neutrals big 30-loop pigtails making for a quite impressive air-core inductor coil, and then expect you to straighten it and tell you to cut it to length!)  *BUT* having cut it, you should crimp on a ferrule, like the mfr did, to protect the very fine Extra-Flexible strands of the Class 6 conductor from the force of the terminal screw.  MEM even instruct you to that, but most mfrs don't because (and here's a notable difference in professional practise) in much of Europe it is fully expected (almost compulsory) that a professional sparky will ferrule any stranded conductor before termination (except when using a cage terminal designed for that conductor size, rather than a screw terminal).  Over here, ferrules are still highly uncommon outside of panel-makers using small size wires in larger terminals, which is fine when a professional sparks habitually twists up the strands (and doubles it over in larger terminals) to spread the load caused by a screw terminal.  But when can’t-be-arsed amateurs leave the strands 'parallel' (with only the slight construction lay) and doesn't think to bend over smaller conductors, then the force of the screw terminal will damage 2 or 3 of the precious 7 strands of a normal stranded conductor, and a great many fine extra-flexible strands of a tri-rated cable, which may well break at that time or will likely fracture as soon as it needs to be released for testing, alteration, etc.  The effective reduction in cross-sectional area can often create hazardously hot terminations making insulation creep back and softening the remaining strands.

(Sorry for that off-topic rant, as an inspector I just triggered one of my own hot-buttons…)

2) Yes, you need proper test results from an installation (multi-function) tester to determine whether the RCBO is at fault (if the RCD is over-sensitive or reacting badly to DC current from digital circuitry) or the circuit conductors are leaking to earth (e.g. damp old cables of excessive length).  So if you’re not a sparky and have no proper tester, you need to get in a professional!  (In this instance I assume Mr Sakho is such a person, so my first advice him would be to do a ramp test on each RCBO to ensure it doesn't trip sooner than mfr specs, for instance iirc SquareD once told me their 30mA RCCB/RCBO must trip at >18mA.)

Otherwise it will be pure guesswork, although you can use trial-and-error logical experimentation to determine if one or more current-using devices or switching points are at fault.  For instance, cheap poorly made LED lamps may have controller faults that upset an RCBO, so swapping them out and trying them each in a single fitting using a single light switch may tell you something, or switching on different combinations and counting the number of lamps that cause a problem (combined leakage) or trying to turn on a number simultaneously (LEDs are notorious for their in-rush current) which may not be easy.  The alarm panel causing a trip is more worrying and begs for a competent person to disassemble it to closely inspect all joints and components.  But again, without test results you may be completely wasting your time examining the box when the fault is rodent damage to the circuit cable

I once stripped out a consumer unit which had been installed with 25 mm boot lace ferrules on the seven strand 25 mm tails into the cage clamps of the main switch without the ferrules having been crimped.


I pulled the ferrules off with my fingers and reinstalled the tails into the cage clamps of the new main switch without them. Having watched a few people on YouTube supposedly doing a "good job" by sticking ferrules on the ends of conductors that are being terminated into cage clamps it soon becomes obvious some of them don't know what they are for, often the same people who don't shrink heat shrink or cut it very short ?