1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Shower upgrade, MCB rating?

Discussion in 'Electrics UK' started by lasors, 16 Apr 2012.

  1. lasors

    lasors

    Joined:
    5 Nov 2009
    Messages:
    185
    Thanks Received:
    13
    Location:
    West Midlands
    Country:
    United Kingdom
    Hello all,
    We're upgrading our shower from an 8.5kW to a 9.8kW (@240v). Consumer unit currently uses a 40A Crabtree MCB (61/B40) and wiring is 10mm with no more than a 6m run, surface clipped.

    Crabtree don't make a 45A replacement, which is the rating advised in the shower manual. Will the 40A one currently installed be ok?

    Thanks!
     
  2. Sponsored Links
  3. lasors

    lasors

    Joined:
    5 Nov 2009
    Messages:
    185
    Thanks Received:
    13
    Location:
    West Midlands
    Country:
    United Kingdom
    Having said that, will a type B MK 45A fit as a direct swap or are they incompatible with Starbreaker consumer units?
     
  4. JohnD

    JohnD

    Joined:
    15 Nov 2005
    Messages:
    73,487
    Thanks Received:
    4,230
    Location:
    Crossgates, Europe
    Country:
    Cook Islands
    incompatible.

    Also, there are two sorts of Starbreaker MCB, one with a screw at the bottom and one without.

    By my calculation 9800W/240v is 40.8A which is near enough.
     
  5. riveralt

    riveralt

    Joined:
    4 Jan 2004
    Messages:
    4,020
    Thanks Received:
    597
    Country:
    United Kingdom
    You should be guided by the manufacturers instructions which will indicate the size of the MCB you should use.
    The 9.8kw @240v rating is just for the outside of the box - the instructions will give you a figure around 9kw @230v and a 40Amp MCB rating.
    They will also say that the new shower MUST also be additionally protected by an RCD.
    Change the MCB and you're are into notification terriority.
     
  6. lasors

    lasors

    Joined:
    5 Nov 2009
    Messages:
    185
    Thanks Received:
    13
    Location:
    West Midlands
    Country:
    United Kingdom
    It does give figures of 9kw@230v as well, but also says it requires a 45A MCB, which is what confused me.

    The shower MCB is part of a group protected by a 30mA RCD.

    So even if I wanted to replace the MCB, I can't do it without paying building control to inspect?
     
  7. JohnD

    JohnD

    Joined:
    15 Nov 2005
    Messages:
    73,487
    Thanks Received:
    4,230
    Location:
    Crossgates, Europe
    Country:
    Cook Islands
    you could have it done by an electrician who is a member of a self-certification scheme, which is very likely to work out cheaper and easier.
     
  8. riveralt

    riveralt

    Joined:
    4 Jan 2004
    Messages:
    4,020
    Thanks Received:
    597
    Country:
    United Kingdom
    I take it is a Mira shower then!
    They appear to have moved the goal posts recently by moving the 9.8kw shower to 45Amp MCB. Odd since the purpose of the MCB is to protect the cable which in your case is rated at 63 Amps.
    You could always ask Mira or whoever the manufacturer is, if it will be okay to fit a 50Amp MCB since you are using 10mm cable and crabree don't make a 45Amp - though again there is the notification issue again.
    The alternates are notify and do it yourself.
    Employ an electrician, member of a competent persons scheme, who could either fit a 50Amp if allowed or fit a shower CU with its own 45Amp MCB/RCD next to your current cu.
     
  9. lasors

    lasors

    Joined:
    5 Nov 2009
    Messages:
    185
    Thanks Received:
    13
    Location:
    West Midlands
    Country:
    United Kingdom
    It is a Mira shower, yes. An Azora.

    I've seen the option of upping it to a 50A discussed elsewhere, so that might be the way to go.
     
  10. Sponsored Links
  11. plugwash

    plugwash

    Joined:
    28 Mar 2004
    Messages:
    9,530
    Thanks Received:
    374
    Country:
    United Kingdom
    Personally i'd just leave the 40A MCB in place. It's in-spec at 230V and very nearly in-spec at 240V
     
  12. scousespark

    scousespark

    Joined:
    18 Jan 2006
    Messages:
    1,127
    Thanks Received:
    68
    Location:
    Merseyside
    Country:
    United Kingdom
    No it isn't (for either voltage)
     
  13. JohnD

    JohnD

    Joined:
    15 Nov 2005
    Messages:
    73,487
    Thanks Received:
    4,230
    Location:
    Crossgates, Europe
    Country:
    Cook Islands
    hey scouse

    what do you think the current is at 230v then?
     
  14. sparkwright

    sparkwright

    Joined:
    20 Aug 2009
    Messages:
    8,597
    Thanks Received:
    1,082
    Location:
    Dorset
    Country:
    United Kingdom
    Even worse at 230, surely?
     
  15. EFLImpudence

    EFLImpudence

    Joined:
    7 Jul 2010
    Messages:
    37,086
    Thanks Received:
    4,161
    Location:
    Retired to:
    Country:
    Portugal
    42.5A @ 250V
     
  16. sparkwright

    sparkwright

    Joined:
    20 Aug 2009
    Messages:
    8,597
    Thanks Received:
    1,082
    Location:
    Dorset
    Country:
    United Kingdom
    :oops:

    Ah yes, 9 kW at 230 v, my mistake.
     
  17. ban-all-sheds

    ban-all-sheds

    Joined:
    27 Aug 2003
    Messages:
    69,782
    Thanks Received:
    2,858
    Location:
    London
    Country:
    United Kingdom
    How would that work?
     
Loading...

Share This Page