Replacing an RCD with a Mains Switch?

Discussion in 'Electricians' Talk' started by Sploo, May 5, 2018.

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  1. Sploo

    Sploo New Member

    JP - yes it's an SWA from the house to the garage (mentioned in post #8).

    All - As for finding the fault; as I've noted, it's an intermittently dodgy NVR switch on my drill press that is the "fault", but in reality it's highlighted the much more serious danger of the wife tripping the house RCD (by running over the lawnmower cable), and leaving me in the dark... with my digits rather too close to a spinning finger remover. I.e. the thing which is causing the tripping is a theoretical (but very real) possibility.

    At the moment, if something causes a fault then the house RCD (in the "shower unit" CU that's supplying the garage) is tripping first - even though the circuits in the garage are now on RCBOs. Ideally I'd be able to leave the house RCD (to protect the SWA to the garage, plus lighting circuit) but for the RCBOs in the garage to trip first.

    For clarity; the current configuration is...

    "Shower unit" CU in house that supplies the garage:
    40A MCB + 63A 30mA RCD

    ...SWA cable to garage...

    CU in garage:
    6A MCB (lights) + 32A RCBO (ground floor garage sockets + roller shutter door) + 32A RCBO (upper floor sockets - i.e. wife with lawnmower) + 100A Mains Switch

    Originally the two 32A RCBOs were 32A MCBs (that's all I've changed).

    So - could I either replace the 63A RCD in the house CU with a 63A Mains Switch, or possibly do that *plus* replace the 40A MCB in the house with a 40A Type C RCBO (in the hope that the Type B RCBOs in the garage would trip first in the case of a fault with one of those circuits)? My thinking there is that the Type C RCBO would still offer some protection if someone managed to hit the SWA cable with a chainsaw.

    I am of course assuming that if you effectively have the following in series...

    (Windfarms, coal power stations, and argent energy devices) <-> (63A Mains Switch) <-> (40A Type C RCBO) <-> (32A Type B RCBO) <-> *fault on circuit*

    ...then the Type B RCBO would trip, but the Type C shouldn't?
     
  2. spinlondon

    spinlondon Screwfix Select

    The type B or C refers to the MCB component of the RCBO.
    The RCD component of the RCBO will still trip at around 30mA.
    It will still be hit and miss as to which device or if both would trip.
    You need to remove the danger presented by the lights and the roller shutter losing power because of a fault on an un related circuit.
    To achieve this, yo need to change the RCD in the shower Consumer unit to An isolator (main switch).
    Leave the 40A MCB as is.
    Run a separate circuit in the garage for the roller shutter on an MCB, or add the roller shutter to the 6A lighting circuit.
    That way if an earth fault develops on the socket circuits or anything plugged into a socket, you will not lose power to the lights or the roller shutter.
    You may have to up rate the 6A MCB for the roller shutter, then feed the lights via a 3 or 5A FCU?
     
    Last edited: May 7, 2018
  3. Sploo

    Sploo New Member

    Spinlondon - many thanks; that's very useful info.

    I'll check the current requirement for the roller shutter door, but I could indeed up-rate the lighting MCB and use an FCU. I'll look into that.
     
  4. Risteard

    Risteard Screwfix Select

    An RCBO is an RCD.
     
  5. Sploo

    Sploo New Member

    Risteard - yup, but read the long version :) (I know an RCBO is an MCB+RCD)
     
  6. Risteard

    Risteard Screwfix Select

    I know. Often people talk about "RCBOs and RCDs" when they really mean "RCBOs and RCCBs".

    RCD is a generic term for all such devices. An RCBO is every bit as much an RCD as an RCCB, SRCD, PRCD etc.
     
  7. Coloumb

    Coloumb Screwfix Select

    What? Are you being serious? A RCD is totally different from an RCBO. How can you state they are both the same when they have totally different functionality?

    Or do your replacing an MCB with an RCBO you quote your customers "I'll fit you an RCD in there"? Pfffft.
     
  8. Sploo

    Sploo New Member

    Let's keep it polite guys...
     
  9. Risteard

    Risteard Screwfix Select

    WRONG. WRONG. WRONG. WRONG. WRONG.

    An RCBO is an RCD.
    An RCCB is an RCD.
    An SCRC is an RCD.
    A PRCD is an RCD.

    What you are trying to state is that it is different to an RCCB - RCD is the generic name for ALL such devices and is NOT synonymous with RCCBs.

    I suggest you read Part 2: Definitions as you clearly are not conversant with BS7671.

    Incidentally, the term "MCB" you used is not recognised by BS7671. That term was removed from the Standard when the 16th Edition was withdrawn. The 17th Edition refers to them as "circuit breakers".
     
  10. Coloumb

    Coloumb Screwfix Select

    So your replacing an MCB with an RCBO - you tell your customers "I'll fit you an RCD in there"? Pfffft.

    Get.

    Over.

    Yourself.
     
  11. Joe95

    Joe95 Screwfix Select

    If you look closely, you can see Risteard disagrees with Coloumb! :D
     
  12. Coloumb

    Coloumb Screwfix Select

    Aye well it all descends in to farce tbh. Probably get's a bit boring for everyone else. But he is such a weapon I can't resist. :D
     
  13. Risteard

    Risteard Screwfix Select

    "Get is" what?

    Oh, I see.

    WRONG. EPIC FAIL BY AN EPIC FAILURE.
     
  14. Coloumb

    Coloumb Screwfix Select

    @Joe95 see what I mean. :D Whit a tard.
     
  15. Coloumb

    Coloumb Screwfix Select

    Hi Lee. It was only a question of time wasn't it mate. :rolleyes:
     
  16. HappyHacker

    HappyHacker Active Member

    Apart from all the above I would add an emergency light to the lighting circuit in the garage. Then if the power to the lights fails the emergency light will come on and give you light to solve the problem or open the door. They are quite cheap (Less than £20) in the overall scheme of things.
     
  17. Sploo

    Sploo New Member

    Yea I was thinking of something like that. It's always possible the whole house goes off (simple power cut etc), and that would make things safer. I only need something that'll last for 5-10 minutes; as that's long enough to disengage the roller door and lift it.
     
  18. Sploo

    Sploo New Member

    Closing this off with thanks to all who gave advice - I've replaced the RCD in the house with a Mains Switch, and confirmed that a problem in the garage will now only trip the RCBO (in the garage CU) that's driving the relevant circuit (i.e. I don't lose the lights).

    I've also replaced the NVR on the drill press.

    I've not yet found a suitable emergency lighting product (just in case there's a full power cut, or the house trips out, and I'm in the garage with the door closed) but I'll keep searching.
     
  19. spinlondon

    spinlondon Screwfix Select

    LED strip lights.
    Give out about the same light levels in emergency mode as in normal.
     
  20. Sploo

    Sploo New Member

    The garage currently has round LED lights, flush mounted in the ceiling. They look good, but the light they put out is kinda "funky". I believe the cheaper LEDs don't put out light at some wavelengths, so, especially under photography, the results are a little weird.

    Unfortunately, I can't currently practically get access to the wiring in the ceiling cavity (at a sufficient level to add more lights or replace them with different shaped units). For that reason, I found, and have just obtained, an LED non-maintained bulkhead light, which I plan to wire into the lighting circuit and mount near the CU. As I understand, it'll illuminate (from its own internal battery) when the power is lost... which will cover the safety aspect of ending up in the dark in a room full of sharp things.
     

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