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Which RCD for Garage Consumer Unit, mains coming from house

Discussion in 'Electrics UK' started by Squiral1, 17 Sep 2020.

  1. AndyPRK

    AndyPRK

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    well yeah ok, that's a different argument.
    Consider over current protection ATM
     
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  3. RF Lighting

    RF Lighting

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    I’m still interested as to why there are so many cables at that CU for just two circuits.
     
  4. AndyPRK

    AndyPRK

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    yeah, its alot.
    Maybe lots of lights.

    OP says he may want an oven and hob in the garage :ROFLMAO:
     
  5. ericmark

    ericmark

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    [​IMG] The type of RCD is under the switch, the [​IMG] shows type, and I would have expected a garage to have type [​IMG] at least, so I would say no it should not be connected to the same RCD. However the regulations don't say you should not use type AC [​IMG] they just suggest your should use the appropriate one for the type of load.
    The problem is if any circuit connected to that RCD has a DC component then it could stop it working, using RCBO's instead of the RCD and MCB as least means if one circuit has a DC component only that circuit is affected. Since we typically test an RCD with everything switched off we can miss the fact it will not trip due to inverter washing machines, fridge/freezers and the electric car charging point, in fact in the main it should be type F [​IMG] for electric car charging points. But we have no idea what you have in the house or garage.
    However as to if you really want to reconfigure the existing CU is another story, it does have the bus required to take RCBO's so could be done, but the test gear is costly and really not the sort of job for a DIY man, really the DIY man should not touch the consumer unit.
    I will admit I don't have the test gear, I have a RCD tester, but not a clamp on ammeter that will measure 0.001 amp or 1 mA and you should ensure the no fault drain is no more that 9 mA, so in my own house it is all RCBO's. It could be said with SWA cable the RCD protection should be in the garage.
    However likely if you get an EICR done it will not get a C2 code, and it can be argued it does not need type A but you ask if it should come from same RCD and being pedantic no is the answer. Although I am sure there are 1000's of homes where loads of IT equipment is supplied from type AC RCD's and of course also 1000's of homes with no RCD at all.
    I am assuming the question should have been "Should the armoured cable going into the garage consumer unit be connected to a same B32 MCB/RCD combination to rest of house? Is that ok? or should it be a different RCD?" The main reason I would not use same RCD is if you trip it then part of house loses power, which could mean things like cordless telephones not working, and fridge/freezer starting to de-frost, secondary reason is the old battery charger could stop the RCD tripping. But there is no hard and fast rule, if you want to take the chance, then there is nothing stopping you.
     
  6. Taylortwocities

    Taylortwocities

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  7. Squiral1

    Squiral1

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    A lot of advise there guys... Understanding parts of it, but not all !!

    The building is an outbuilding, a man cave, so will have av equipment (TV etc) . And thinking of putting a kitchen in there later to host parties. For phase 1 I just wanted to get power to it and second fix the sockets and lights. Second fix the sockets and lights I can do no problem.

    Need to do the right thing re the power

    But maybe it's not a DIY job!
     
  8. AndyPRK

    AndyPRK

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    Arh. You’re nearly there.
    Just need to connect a few wires up
     
  9. ericmark

    ericmark

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    I like the idea of a man cave, I have what was used as a granny flat by previous owners, full kitchen, bath/shower/toilet room, bedroom and living room. But wife uses it for storage.

    But the power requirements electric wise are low, it is nearly actually a cave being under the main house, it is heated with the same oil fired boiler as the house, and it is heating which is the main thing about a man cave/shed.

    If your going to use bottle gas for example for heating, then likely all you need is a fused connection unit (FCU) and a switched one for the lights with 3A fuse. Likely you can get away with up to a 2 kW panel heater, but over that and you start looking at a much more complex system. The man cave with electric heating can use more electric power to the house.

    My cave stays cool in summer, as said near enough is a cave, but if you need an AC then volt drop has to be considered, same with fridge or freezer, unless expensive inverter control refrigeration units can be damaged with volt drop, and also frost free needs a minimum temperature to work in.

    In my case the main supply is to the granny flat, it was a garage, and house is supplied from there, so I have no power problems, electric shower, oven, and 4 ring hob, but had it not been part of main house, that would take a lot of doing.
     
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  11. Squiral1

    Squiral1

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    Thanks ericmark. So my man cave will be similar, eventually will look at have a fridge freezer in there and maybe a hob oven etc.
    There is a 10mm wire for the oven which I will put on a separate MCB.

    So I think I'm going with connecting the armoured cable in the man cave to a 32A MCB, which matches the house, the armoured cable is buried inside concrete, but I will earth it.
     
  12. winston1

    winston1

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    NO. As TTC said in post 11:

    You must have discrimination between up and downstream devices. The downstream must be quite a lot smaller than the supply end, otherwise in the event of a fault the house MCB will trip.
    Good installation design provides localisation of fault. You go not have good installation design.

    Also read my post 2 where I said you don't need a CU in the "cave" at all. Connect your ring directly and use a switched FCU with a 5 amp fuse for the lights.
     
  13. EFLImpudence

    EFLImpudence

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    Apart from the fact that there is no point having a 10 square mm (10mm²) cable if the supply is 32A,
    you do not need 10mm² for a cooker (oven and hob).
    4mm² is all you need for a 32A MCB and will do for any domestic cooking appliances you will buy.

    I think you should get an electrician.

    Outdoor electrics is not a DIY job.

    What about bonding? Do you know what it is?
    You might need a 10mm² bonding conductor from the garage back to the house.
     
  14. Squiral1

    Squiral1

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    how much smaller?

    Yes you might be right, it does seem there are different options, and a pro can look at the whole set up in details and advise I guess
     
  15. AndyPRK

    AndyPRK

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    The Mcb goes on the supply end.

    OP. In that small CU, you would normally have a (double width) red main switch or an RCD. Do you have either of those already? What brand is that small one
     
  16. Squiral1

    Squiral1

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    I have MCB in the supply end, a 32Amp

    The cave CU is British General which has an RCD 40A 30mA, MCB 32A and MCB 6A
    So can use one of these for the armoured cable from supply
     
  17. AndyPRK

    AndyPRK

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    Yeap.

    Fit them in.
    Supply goes into the RCD top connections.


    Then you have a copper bar out the bottom to connect live into the 2 MCBs

    Neutrals connect right at the top of the unit
     
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