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upgrade to a dual RCD board (volex)

Discussion in 'Electrics UK' started by HawkEye244, 25 Sep 2020.

  1. HawkEye244

    HawkEye244

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    Hi all,
    In the process of upgrading this volex 100A.
    I'm aware of the problems with the bus bar and that will be sorted.
    Just wanted to know if it's acceptable to fit another RCD on the left for the lighting circuits and of course bring some MCBs over from the right as that side is overcrowded, or is the board not designed for that sort of upgrade?
    If the answer is yes, would it be ok to source the same VR80 spec that's currently being used or would a VR40 (40A) be more suitable for the lighting circuits?
    Many thanks as always

    SSN499QR.jpg
     
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  3. Taylortwocities

    Taylortwocities

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    An RCD will be an additional double width item. You do not have room! Your option is to (try and) find a couple of 6A VOLEX RCBOs for the lighting circuits. If I think back, the last time I tried to do that it was a nightmare. The VOLEX board isn’t really tall enough to enable RCBOs.

    VOLEX is not a well regarded brand, not sure if it’s even sold new anymore. Better to junk that and have a Whole new, compliant board.
     
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  4. sparkwright

    sparkwright

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    If ypu absolutely must keep the old board, you could remove the RCD and all the MCBs, and fit all RCBOs with a new long busbar.

    That will give you two additional spare ways for the future, and if there is a fault on one circuit, all the others will work.

    But as Taylor says, by the time you've done that you may as well have fitted a brand new board.

    All RCBOs is the way to go.
     
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  5. AndyPRK

    AndyPRK

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    The are just electrum boards.

    I’m sure the older wylex rcbo would fit.
    Not sure about height though.

    I can’t find you 3 on ebay though.

    https://www.ebay.co.uk/itm/313146132104



    Fitting a new board would seem more sensible.
     
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  6. ericmark

    ericmark

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    For all RCBO your looking at around £150 just for the RCBO's some makes a lot more, just not worth keeping old board.
     
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  7. flameport

    flameport

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    The only upgrade is to remove that lot and install a new board.

    Volex consumer units haven't been sold for the better part of a decade, finding parts for it will be next to impossible, the RCDs are the wrong type, the enclosure is made of plastic, a dual RCD board is a poor choice for any installation and won't comply with BS7671 for a majority of them.
     
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  8. HawkEye244

    HawkEye244

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    There is enough room on the din rail to accommodate another RCD. My mistake is not taking a suitable photo!
    Bus bar replacement is on the way so I will have enough room.
    I can only find a vr40 rcd and I'd like to know whether it's suitable for the lighting circuits. I note that mostly all CUs now come with 63A RCDs. I understand the importance of them being 30mA. I don't understand RCD sizing though?
     
  9. HawkEye244

    HawkEye244

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    Why is dual RCD a bad choice and not compliant with BS7671? Will it therefore be picked up on a EICR? Fitting an RCD for the lights is in the interests of safety but this is not considered safe or suitable ?
     
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  11. JohnW2

    JohnW2

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    I'm sure that flamport will give you his answer but I would point out that (a) many people probably don't agree with him and (b) I would imagine that a dual-RCD board is easily the most common type of CU in service in UK domestic installations (i.e. there are countless millions of them in service).
    Givcen that some people will presumably share flameport's view, it seems likely that it might be 'picked up' during an EICR. However, one would hope that even flameport would only give it a 'C3' (i.e. not 'unsatisfactory'/'fail') - which the board quite probably would get, anyway, because it's plastic.
    I don't personally see it as a significant safety issue, but BS7671 does now effectively require RCD protection of lighting circuits (although, as always, that is not a 'retrospective' requirement).

    Kind Regards, John
     
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  12. ericmark

    ericmark

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    The EICR is about safety, not complying with BS7671, it was at one time, but code 4 was removed as it was considered as confusing. In the main electric tripping does not produce a danger, so would not be flagged up.

    Lighting has a maximum size of 16 amp for the trip, and in most houses since the ceiling roses are rated 6 amp, 6 amp is maximum size of a lighting circuit.

    A RCD has a number of ratings, typical 10kA for how much is can safely switch off once when there is a fault, then 80 amp for how much it can handle on a continuous basis, and 30 mA the maximum imbalance it will allow without tripping and type AC, A, F, or B for how it can handle DC and high frequency AC.

    The MCB also has three ratings the 10 kA the amps it will trip with in due time and the amps it will trip with within 0.01 seconds. So a B6 MCB will trip in time at 6 amp but very fast at 30 amp (5 x 6 amp) and a C6 very fast at 60 amp (10 x 6 amp).

    So each circuit in theory you need to test to see what size the maximum MCB can be, so 30 amp at 230 volt needs an impedance of 230/30 = 7.66Ω pull some safety 5% so 7.28Ω and we use a loop impedance meter to check it.

    The problem it the meters used are expensive, so not really worth the DIY guy knowing how to do it, as he is unlikely to have the test gear, and the MCB is not normally tested as such, so never use second hand as you don't know if they have been damaged.

    With an incoming DNO fuse of 60 amp a 63A RCD would be OK, however we often have 80 or 100 amp supplies, so often we look as the total MCB load, not really cut and dried, but you could not say an inspector is wrong if he fails an installation because the MCB load is likely to exceed 63 amp, it is his judgement.

    As the owner or landlord your job is simply to select some one who has the skill, you don't need to have the skill yourself, but I can see how the owner or landlord wants to know what is really required as there are so many trying to drum up trade and want to do unnecessary work, but many be the landlord should also worry if something goes wrong will he get the blame. The courts to me are biased towards the tenant when things go wrong. Even when it seems the tenant has not been very sensible. So I decided to sell old house not rent it out.

    I can hardly believe some of the things tenants expect the county council to fix with council houses, and one does not want to be called because a RCD is tripping, so I would consider fitting RCBO's so no excuse for calling anyone out, but distance from house could change that, I had a 100 mile round trip.
     
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  13. Taylortwocities

    Taylortwocities

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    Sorry to be critical, but if you do not understand that, then maybe you shouldnt be messing around inside a consumer unit.
     
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  14. JohnW2

    JohnW2

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    In my experience, that's not how many (most?) people undertaking EICRs see it. They seem to feel that any non-compliance with BS7671 has to be 'flagged up' on an EICR. However, as you go on to say, there is a bit of a problem resulting from the loss of a C4 (or equivalent), the result of which is that the very least the inspector can do is to "Recommend Improvement" (C3), whether or not they really think that such a 'recommendation' is necessary/appropriate.
    Just as a matter of detail a B6 is required NEVER to trip at currents less than 6.78A (6 x 1.13).
    Such an inspector could be a big problem if he/she turned his/her attention to Main Switches (as well as many RCDs), which are never rated above 100A in domestic CU's, since the total rating of all MCBs/RCBOs in a CU is often, probably usually, well in excess of 100A!
    That may well have been a sensible decision for you, for any number of reasons but, in terms of what you have said, it's incredibly rare for "something going wrong" in rented accommodation to get into court.

    Kind Regards, John
     
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  15. AndyPRK

    AndyPRK

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    Hawk. If you really want to continue with that board it will be way easier to add 2 or 3 rcbos. (This is a circuit breaker and rcd combined into one unit. Though usually taller)

    Adding an rcd is not sensible as you also need to add a neutral block. And appropriate wiring. Sourcing this will be expensive. And done wrongwill be more dangerous.

    Is the B16 used ? Is it marked water heater?

    Post a full pic of the board from top to bottom
     
    Last edited: 26 Sep 2020
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  16. flameport

    flameport

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    Maximum leakage current is 30% of the RCD rating, or 9mA for a 30mA RCD.
    With multiple circuits on a single RCD, you only have 2 or 3mA per circuit before it doesn't comply, and a single item of equipment can easily be between 0.5 and 2mA.

    There is also the matter of division of installation, which most certainly isn't complied with if someone shoving a knife into the toaster also results in multiple other circuits being disconnected.

    Type AC RCDs were designed to work with resistive AC loads only, which was things like incandescent lamps and electric heaters with mechanical thermostats.
    The vast majority of modern equipment is not suitable for use with that type of RCD.
    Other, more sensible countries got rid of Type AC RCDs 20+ years ago.

    A plastic CU is a C3.
    C3 for having type AC RCDs.
    Minimum of C3 for circuits with no RCD, C2 in some cases.
    C3, C2 may be required depending on what the total leakage current on each RCD was, and exactly what type of equipment was connected to the circuits, and whether the performance of the RCDs was impaired due to that equipment being connected.
     
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  17. JohnW2

    JohnW2

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    Agreed (given that the reg exists), given that there is no C4 available.
    I'm still struggling to find any particularly useful chapter and verse about this 'RCD type' issue, so I find it hard to make any informed judgement. However, IF one believed (as you seem to) that the satisfactory performance of Type AC RCDs is likely to be impaired by the loads in an 'average domestic installation' and IF (which I assume you do) one believed that RCDs were essential/useful safety measures, then I would have thought that having Type AC RCDs (which I think most UK domestic installations do) would deserve a C2, wouldn't it (since it would be analogous to having a potentially faulty RCD)?
    Fair enough. There's obviously a lot of individual judgement involved in what might warrant a C2.
    Given that the issue will most commonly arise because of sockets circuits, I think you might need two crystal balls to be able to apply that - one to predict "what type of equipment was [might be] connected to the circuits" and another to predict "whether the performance of the RCDs was impaired due to that [often unknown] equipment being connected". How, in the absence of such crystal balls, do you actually make that judgement in practice?

    Kind Regards, John
     
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