Electrium consumer unit and RCBO trip why?

Discussion in 'Electricians' Talk' started by Joseph William Smith, May 24, 2023.

  1. Hello to all, I have just joined thanks in advance.
    Due to consumer unit failing landlords test my brother was told he had to replace tenants consumer unit, I am retired but an ex Electrician previously Maintenance but ex contractor,
    We replaced said plastic mcb populated board with RCBOs as well as anti surge protection, thats the short story, however on switch on we keep getting the 6a RCBO tripping only when switching landing light on, having looked at this light we find it has LEDs incorporated with electronic ac/dc driver inside, leaving this off we note nothing trips but supply present at rose, is there any way we can incorporate this light with either a change of device (one that incorporates LED fittings? ) or am i looking at this wrong ? I'm hearing (im assuming its this light that's causing the problems) I did hear the LEDs and the associated circuitry have inrush currents so high they can cause nuisance trips, the light however trips immediately every time, Could it be anything else or failing that is there any device that can still allow us use of this very expensive fitting? currently, its looking as we stand, it cant go back up.
    Advice/help/tips Im hoping there's something that we can do so we can still incorporate this fitting, previously btw it just had mcbs.
    Thanks to all in advance, Joe.
    Last edited: May 24, 2023
  2. Jimbo

    Jimbo Screwfix Select

    If it has a separate driver then that could be replaced, often the exact model can be found online.
  3. sparky steve

    sparky steve Screwfix Select

    My guess is possibly a 'borrowed neutral'?
    when one or more lights uses the neutral of another lighting circuit, rather than it's own. This was often done for convenience, particularly with landing/hall lights.
    If the two circuits are on RCBOs, or different RCDs, then these will trip because the diverted neutral currents will cause an imbalance.

    For a 30mA RCD or RCBO, the current going out down the line and returning down the neutral must be equal - if the imbalance exceeds 30mA it will trip.
    Ps: The led fitting may have a switching PSU ?
    If one of the diodes on the input to the PSU is open circuit, it will cause half wave rectictification of the supply. This will cause an imbalance in the RCBO and cause it to trip.
    Last edited: May 24, 2023
  4. ElecCEng

    ElecCEng Screwfix Select

    Electrium RCBOs should be type A which would help. Ideally you would have tested prior to ‘switch on’, which would have identified this issue. I would go back to basics and do the continuity and IR tests on the circuit. The values you get should point to the problem area.
  5. Ind spark

    Ind spark Screwfix Select

    Try putting the 2 lighting circuits in the same rcbo, bet it works.

    Then you'll need to split the circuit it wont be easy if decorated.
    The Happy Builder likes this.
  6. MGW

    MGW Screwfix Select

    I would also say borrowed neutral, actually a borrowed line, years ago only twin and earth was run between the switches and the line for the remote switch was taken from an adjacent switch, this is OK if on the same circuit, but then some one would split the circuits up/down so need to use something like kinetic switches as not enough wires between the switches.

    Or re-combine upper and lower lights of course.
  7. adgjl

    adgjl Screwfix Select

    Were the circuits fully tested / partially tested / not tested at all apart from the “bang” test when the consumer unit was replaced. If it hasn’t been tested properly and documented, you will likely need to get another EICR done, but if whoever replaced the consumer unit was not a scheme member, you are likely to be in breach of Part P of the building regulations as well.
  8. The Happy Builder

    The Happy Builder Screwfix Select

    That is almost certainly the answer.
    Ind spark likes this.
  9. Cheers for answers, as I say if i remove the fitting nothing trips, borrowed neutrals why, the up and down are separate circuits, the landing neutral surely is with upstairs circuit? why would you borrow one?
    What would you test before switch on? its already under certification, the advisory was the board being plastic he was told, the test will still have to be done afterwards, we are just trying to find out why this one light seems to trip that particular circuit. Seems to be more a panic about test, dont worry it will still need certification, surely the RCBOs are better than what was there previous, short/overcurrent protection. Rating answer may be another option, The wiring is under certification it was already passed! As a landlord you get a certain time limit to act on advisory, that's what we are doing.
  10. Ind spark

    Ind spark Screwfix Select

    Before rcds came about electricians would use the live from the downstairs circuit and the neutral from upstairs, wrong but works fine without rcds.

    If the light fitting is causing the fault why not just replace it?
  11. Years ago they did, but most now are separate up and down, surely no need to borrow anything, my main concern is the fitting he has (landlord) is a very expensive 4 long leds, (£80) It worked fine with mcbs previous its very bright (stairs illumination) now it trips when turned on, all im doing is trying to find out why, searches give me spikes, dc drivers, inrush currents etc, I was only wondering if anybody else has had this with led type fittings (ones with internal drivers) it points to this because once removed nothing trips?? Unless i can find out reason why, your right it will have to be removed, all other lights are on and working, had to put a bulb up for now but ITS NOT what was there. Thanks for reply, I hope that answers. It will obviously need certificating again asap (to those who are asking question) Previously only mcb but nothing ever tripped.
  12. Ind spark

    Ind spark Screwfix Select

    Ok if the wiring is newer then no probably nothing borrowed.

    I've never had the problem you are having.
  13. PaulBlackpool

    PaulBlackpool Screwfix Select

    If this fitting has been removed can you wire it to a 13 amp plug with a three amp fuse fitted and plug it into a socket?
    If it trips that circuit the light fitting is faulty . If it does not trip the wiring to the lighting circuit is faulty.
    I am just a layman but I did not think that led lights have massive inrush currents as the load is so small.
  14. No, quite simply the sockets are on a 32amp RCBO, Its higher rated, 6a recommended for lighting, as for the second part google " can led fittings cause the RCBO to trip" look at the what comes up! Happens apparently, but I'm not 100% sure whether that's case here, going off answers.
  15. The Happy Builder

    The Happy Builder Screwfix Select

    With all due respect, it doesn't sound like you should be doing this work.

    Are you registered as a competent person, how will you notify the work, do you have testers, insurance and so on, will you certify it do you have relevant experience, are you working to the current standards, does the consumer unit meet the current standards?
    Ind spark likes this.
  16. The Happy Builder

    The Happy Builder Screwfix Select

    You are assuming that the person who did the EICR did not miss a borrowed neutral.
    Ind spark likes this.
  17. Bit of an insult that, im 50 years in the field, no im not registered but competent, the work will be tested , the board has been changed, yes I have experience, yes im working to standards, the devices are surely better protection, the boards brand new read the post??
  18. MGW

    MGW Screwfix Select

    In the main borrowed neutrals are because only two core and earth fitted between upper and lower two way switches, so looking at this diagram two-way-real.jpg there is a permanent line to both switches, so one can get away with two core by using the line from an adjacent switch, as long as the adjacent switch is supplied from same circuit (overload device) it is now considered bad practice, as it can cause interference with hearing aids, but it was general practice before the hearing aids were in use.

    The problem is although the two switches may have originally come from same supply, we a one point when mad with lighting using things like GU10 down lights so the 6 amp supply was no longer enough, since the ceiling rose is used as a junction box, and is rated at 6 amp, one could not simply swap to a 10 or 16 amp MCB, so the normal method was to split the circuit into upper and lower floors.

    It was very easy to miss that the landing lights had used two core cable between the switches, not until we started using RCD's did we realise there was a borrowed neutral, once found of course it should be corrected, putting both MCB's on the same RCD is no a permitted method, although using one MCB for both circuits combining them back into one circuit is permitted, but the aim is to have sockets and lights in any room from different RCD's so if some one gets a shock, they are not plunged into darkness. Also where the RCD's are less than 100 amp rated, needs to look at the loadings of the RCD's.

    For a standard side to side split with sockets which is better than up/down as better loop impedance and no temptation with a fault to run cables up/down stairs, you can't split the load around the RCD's with just two, when the lights are up/down split, but the pre all RCBO consumer unit only had two RCD's, so electricians cut corners and broke rules, and that includes myself, one had the make the best of a bad job.

    With RCBO's the borrowed neutral can't exist without tripping the RCBO, so again simple way around the problem is combine the two floors, and by doing so one is proving it was a borrowed neutral and not some thing else. Even if temporary until kinetic switches or the like fitted.

    The problem with the EICR there is no hard and fast rules as to what should be tested, it has been an accepted practice to test just a sample with commercial premises, the sample size being increased if there is a failure, so borrowed neutrals can be missed, in real terms so common to find with stair lighting it should always be tested, but it is down to the inspector and person ordering the inspection to agree what is tested.

    It has been a common practice to include in the notes observations made, like lack of smoke alarms, but this is really for the fire safety officer to highlight, there is no electrical safety issue where they are missing. There is a safety issue, but not an electrical safety issue. But it seems some inspectors have been including things outside their remit. But one can hardly get upset when any safety issue is highlighted.

    This however can result in some one not qualified being asked to correct faults, and electrician is not always trained to know where smoke alarms should be fitted for example.

    OK this is about a RCBO tripping, but the rules require who ever corrects the faults to be qualified to do that work, and from the length of this thread it seems your not qualified to do the work involved, you do need to fine some one trained to do the work.

    I know it sounds like an insult, but we are going by your replies, and it seems the inability to understand the problem. We all have senior moments, where we miss something, I hope it's just one of those with you, but only you know that.
    Joseph William Smith likes this.
  19. Ind spark

    Ind spark Screwfix Select

    Do what @PaulBlackpool said wire the light to a flex and plug it in.

    Show us a picture of the board you've replaced.
    PaulBlackpool likes this.
  20. Bob Rathbone

    Bob Rathbone Screwfix Select

    The 'inrush current' proposal is most likely the issue if a neutral has not been borrowed. The inrush is caused by a filter network on the supply side of the LED driver, a Pi filter with capacitors and choke to prevent the transmission of high frequency signals from the SMPU in the driver, to the house wiring, and to prevent such signals getting into the driver from elsewhere. One of the capacitors in this filter will be between phase and earth, when it initially charges on the first cycle of AC, enough current flows to trip the RCBO. The real issue is that the RCBO is too sensitive and needs a time delay.
    Joseph William Smith likes this.

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