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Second Opinion on Rewire

Discussion in 'Electrics UK' started by shadybrady, 8 Mar 2007.

  1. shadybrady

    shadybrady

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    My electrician has advised me of the following for a rewire :

    Hager Split load Consumer Unit 18 way.

    Earthing system is TNS and the electrics are 1960's except for the earthing which was updated from TT to TNS about 10 years ago when a new ring main for the kitchen was installed. Even though it is only about 2mm thick!

    Consumer Unit as follows :

    RCD circuits - 4 32A ring mains (3 downstairs & 1 upstairs)

    Non-RCD circuits - 4 6A radial light circuits (2 up & 2 down)
    - 1 6A for Smoke alarm circuit
    - 1 40A Circuit to garage separate 2 way CU inc RCD
    - 1 16A Immersion Heater Circuit
    - 1 6A for Bell?? Maybe use separate transformer?

    Hager only go from 12 way straight to 18 way split load supposedly - so rest are spare ways for future upgrades - outdoor socket / garden lights / supply for pond pump - when the garden is done up.

    The question I ask is that many people are advocates of RCBO's and they haven't been mentioned by my electrician, only standard mcbs with some on the side of the main RCD.

    Is it best to use a standard CU and use RCBOs on the ring mains or just stay with split load and mcbs with some RCD protected???

    Electrics need to be done quickly as the lights have no earth and some of the sockets blow the fuses when you plug anything in - also there is no earth bonding on pipework !!

    Any help appreciated

    Thanks

    Shady
     
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  3. Spark123

    Spark123

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    Doesn't seem unreasonable, there is the advantage of only losing one circuit in an earth fault with RCBOs. With using 4 x RCBOs the big disadvantage over one RCD and 4 x MCBs is the price. If your house was upgraded 10yrs ago, surely main bonding was installed then?? Or do you mean supplementary bonding in the bathroom?
     
  4. Adam_151

    Adam_151

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    TT updated to TNS seems rather strange unless you were having a new supply cable fitted for some reason, TT to TNC-S conversion sounds more likely, might want to confirm the exact nature of the earthing system with the DNO

    Not sure Hager make split boards that take 18 breakers... maybe the board is 18 modules wide -2 for switch -2 for rcd leaves you with 14 which is a 7+7 split.. It is indeed the next step up from the ones that take 12 breakers (available as 6+6, or 8+4 or 4+8)... are you are your sparky isn't just reading his price list wrong? ;)

    RCBOs are a good idea, but be aware you'll be paying ~ £40 each for them... although I suppose on a rewire an extra £160 isn't a huge increase
     
  5. securespark

    securespark

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    I speak for John here ( :LOL: ):

    RCBO's are a brilliant idea, because they limit the damage: A split-load RCD will kill all the circuits on it's side of the board. RCBO's will only kill the affected circuit.

    However, I think John will agree with me that fault-finding is not so straightforward as you don't know if the trip is an overload or short-circuit, or due to an earth fault.
     
  6. shadybrady

    shadybrady

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    So is there any 'real' major advantage in using RCBOs rather than the possible inconvenience of resetting all rcd protected circuits if the RCD trips ???

    The earthing is definately TNS - currently I am studying the IEE On-Site guide, Guidance Note 3 , IEE Part P Building Regs Book, the regs and others to improve my understanding.

    Also Isle of Man only has TT and TNS - TNCS don't exist !!

    There is also no EEBADS protection whatsoever - the main gas incomer is in the cupboard next to the incoming supply and there is no earth lead going to it.

    The Hager is 18 way as the supplier can only find 12 way and then it goes straight to 18 - suppose there is no harm to have spare ways in the unit ???

    Does the layout of circuits look ok ??
     
  7. bernardgreen

    bernardgreen

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    One dis-advantage of RCBO is an important circuit ( fridge, freezer, alarm etc etc ) can trip and you are not aware it has as nothing else is affected.
     
  8. JohnD

    JohnD

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    ... unless, like me, you are clever enough to have the freezer and the alarm on their own non-RCD radials ;) If not, you can buy an audible alarm for the freezer and the fishtank heater.

    I hardly ever have an RCBO trip; in the past it has almost invariably been from a steam iron going wrong, and occasionally someone doing something silly :oops:

    But the inconvenience of having to go round resetting timers and clocks is greatly diminished if you only lose one circuit, not to mention the inconvenience of having "everything" go off.

    The chances of nuisance tripping are also greatly reduced, since the "background" leakage is smaller so there is less chance of a transient pushing it over the tripping point.
     
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