What size Armoured cable should I use

Discussion in 'Electricians' Talk' started by An dy1962, Apr 25, 2016.

  1. CraigMcK

    CraigMcK Screwfix Select

    You said use 40A RCD. My comment was that an RCD won't protect the cable
     
    fire likes this.
  2. fire

    fire Well-Known Member

    Aaa yes of course, the RCD alone does not have the capabilities of over current protection. You need combine it with an MCB.

    That means one could use a double pole RCD rated higher than 40Amp in combination with an 40Amp MCB to provide cable overload protection and comply with a double pole isolator for circuits away from the dwelling. You would need 3 available spaces in ones consumer unit though to do that. probably not available at a guess.

    well spotted @CraigMcK thank you.
     
    Last edited: May 1, 2016
  3. leesparkykent

    leesparkykent Well-Known Member

    That's why I asked about it....As you've pointed out the RCD wont provide over current protection. IMO people shouldn't be freely dishing out information especially when its wrong and lack the understanding of something so basic when it comes to designing a circuit :eek:
     
    Risteard likes this.
  4. philthespark

    philthespark Active Member

    RCBO? that would do it and probably work out at a reasonable price,but all in all I think it would be easier to get a professional in and let him deal with it.
     
  5. fire

    fire Well-Known Member

    RCBO's are great but they are only single pole and do not disconnect the neutral, only the line conductor.
     
  6. fire

    fire Well-Known Member

    ignoredargumentover.jpg
     
  7. leesparkykent

    leesparkykent Well-Known Member

    not all RCBO's are single pole solid neutral. Some are single pole switched neutral and some are double pole.
     
    nffc, Risteard and philthespark like this.
  8. fire

    fire Well-Known Member

    I agree, finding them can be a challenge as they are not common to the domestic retailers. You have to look closely at the specs to make sure it is or not and different manufacturers all have their own ranges.
    Most are all 30Ma though so finding a 100Ma double pole RCBO in a 40Amp to feed a mini consumer unit via 6mm2 cable in an outbuilding could be a challenging for the DIY'er.

    It does however bring us back to get a sparky in to actually agree on the job. Designs outside of the normal run of things need parts that are not readily available to the general public and does require a professional supply outlet.

    Before anyone says it, yes the general public can buy from a professional supplier but at a higher price. Talk about equality and discrimination, that said tradesmen do allot more trade and business with the supplier so one does get better pricing based on that alone naturally.
     
    Last edited: May 1, 2016
  9. leesparkykent

    leesparkykent Well-Known Member

    AS they say....little knowledge is worse than no knowl
    I haven't read the whole thread but why does the OP need a 100mA RCD?
     
    Risteard likes this.
  10. fire

    fire Well-Known Member

    He wants to run a 6mm2 cable from his dwellings consumer unit out to a mini consumer unit in his outbuilding and power two circuits on RCBO's, one for sockets and one for lighting.
     
  11. leesparkykent

    leesparkykent Well-Known Member

    why does he need a front end RCD then?
     
  12. fire

    fire Well-Known Member

    It is the double pole isolation that is needed. A standard MCB breaker is again only a single pole.
     
  13. leesparkykent

    leesparkykent Well-Known Member

    If double pole isolation is required why not just put a double pole switch next to the consumer unit and run the circuit through it?
     
    longboat likes this.
  14. fire

    fire Well-Known Member

    Good question, do the new regs requiring double pole isolation for circuits away from the dwelling require it in a automatic protection device or can it be a manual isolation switch as you suggest supplied from a current protective single pole device?
     
  15. leesparkykent

    leesparkykent Well-Known Member

    manual isolation is fine.
     
    fire likes this.
  16. fire

    fire Well-Known Member

    Very cool.

    Not the way i would do it though.

    I'd be laying 16mm2 SWA from a separate isolated fused switch and henly block tails into each. Almost always in the future someone wants to plug in more and more appliances and extend circuits in the outbuilding.

    Everyone is different as is how much they are willing to spend but hey that is just the way it goes.
     
  17. fire

    fire Well-Known Member

  18. Risteard

    Risteard Screwfix Select

    Except when they're not.
     
  19. madhatter1uk

    madhatter1uk Screwfix Select

    That is the only relevant paragraph .
     
  20. Risteard

    Risteard Screwfix Select

    I don't have my Code of Practice on me at the minute but I know it does mention RCDs enabling longer lengths.
     

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