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Changing consumer unit

Discussion in 'Electrics UK' started by OldKettle, 21 May 2019.

  1. OldKettle

    OldKettle

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    Hi,
    Below are a couple of pictures of the consumer unit in my house (located in garage), and I am trying to decide whether to have it changed.

    The main reason for doing so at the moment, is that the cooker circuit does not seem to be under RCD, and I would prefer to have everything put under RCD. I don't know if that could be done with the existing board and, if it can, why it wasn't done initially.

    I plan to have the property extended in the future, eventually want a dedicated kitchen circuit, and also want power to the garden, so I would imagine having at least three new circuits added, so any new unit now would need to accommodate that, and probably a couple more for good measure.

    Would it be most cost effective to just get the board replaced now, perhaps will all circuits on RCBOs?

    Any thoughts would be much appreciated.

    [​IMG]

    [​IMG]
     
  2. EFLImpudence

    EFLImpudence

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    There appears to be room for another RCD if that is what you want. RCBOs obviously.

    Why is the main reason because the cooker circuit is not under an RCD?
     
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  3. OldKettle

    OldKettle

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    Just because I assume that, or all the unprotected circuits, it is the one where people are most likely to be exposed to the risk of shock. That said, I would prefer for them to all be RCD protected.

    Any extensions aren't going to happen for a while, so that is not the main driving factor (just wondering if it would be most cost effective to upgrade the lot now).

    Is there an RCD with enough capacity that it can do the whole CU, or would it definitely need a second RCD?
     
  4. EFLImpudence

    EFLImpudence

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    Not really. The circuit only has to be under an RCD if concealed <50mm. deep in the wall in case you drill into it.
    The MCB will protect you if the cooker becomes live - for a split second.

    Fair enough.

    As you mention 'cost effective' then probably not.
    To be callous, millions of pounds have been spent on RCDs and no one seems to know whether any lives have been saved ( out of very few deaths to start with). Obviously if you were the only one then it would be good.

    One is not desirable because you would lose all circuits with the tiniest fault.
    A second would be very simple to install.
     
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  5. JohnW2

    JohnW2

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    One RCD for the whole installation is not a good idea (and most people would say that it is non-compliant with regulations) because one fault on any circuit would result in the complete loss of electricity to everything.

    Kind Regards, John
    Edit: yet again, too slow!
     
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  6. OldKettle

    OldKettle

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    Thanks. Just out of interest, would an RCD come in to play, if the cooker becomes live and the cooker is not earthed properly?

    If I understand correctly,. if the cooker is earthed, the live contacting the cooker would cause a large current to flow to the earth, tripping the MCB.

    Also, just out of interest, if you do drill into a live cable, would the RCD trip if you managed to hit the live and neutral at exactly the same time?

    If I understand your earlier post, it would be possible to simply get the existing cooker MCB replaced with an RCBO or just get another RCD added to the CU, to cover all of the unprotected circuits.

    Roughly how long would you expect those two options would take a decent electrician? (I had one around to quote for kitchen work, but he looked at the CU and told me that the cooker was already on the RCD, so he won't be invited back)
     
  7. AndyPRK

    AndyPRK

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    I wouldn't change that yet. A good few decades left hopefully.

    Use RCBO's if you want to protect things, like lights.
     
  8. EFLImpudence

    EFLImpudence

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    If you touched it while you were earthed, yes, but just make sure the cooker is earthed.

    Correct.

    No, the MCB. Most drills are Class 2 meaning you would not get an electric shock (just a normal fright shock).

    Yes.

    A couple of hours ???

    :)
     
  9. JohnW2

    JohnW2

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    As EFLI has said, IF that situation arose, then it would be the MCB that tripped.

    However, just for completeness ... that would be an extremely unlikely scenario. Since the (bare) earth conductor of twin-and-earth cable is between the live and neutral, it would be all-but-impossible for a drill (or nail, screw or whatever) to hit both live and neutral without touching the earth - and if it touched live and earth (or, quite possibly, if it touched neutral and earth), the RCD would then trip (unless the MCB had disconnected the supply before the RCD had a chance to do it). If it managed to touch all three conductors simultaneously, it would essentially be pot luck as to whether the MCB, RCD or both tripped.

    Kind Regards, John
     
  10. EFLImpudence

    EFLImpudence

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    Just to add -

    If the bit did touch only Neutral and Earth, then only the RCD would (very likely) trip but this would not be dangerous in normal circumstances.
     
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