RCD and MCB - is this ok for my new shower?

Discussion in 'Electricians' Talk' started by Taddy, Mar 20, 2019.

  1. Comlec

    Comlec Screwfix Select

    Supply voltages are helpfully explained by Schneider
     
    robertpstubbs likes this.
  2. robertpstubbs

    robertpstubbs Screwfix Select

    So the 8500W is just an estimate and dependant on the voltage, whilst the resistance is constant?
     
  3. Pollowick

    Pollowick Screwfix Select

    Correct. MIRA quote 8.5kW for 240v and 7.8kW for 230v
     
  4. robertpstubbs

    robertpstubbs Screwfix Select

    And if the voltage went up to 253V, the power would be 9446W and the current 37.33A?
     
  5. Pollowick

    Pollowick Screwfix Select

    Yes. There will be minor deviations from the values as the element is probably a coil with some inductance although in practice that is normally discounted.
     
    robertpstubbs likes this.
  6. Bazza

    Bazza Screwfix Select

    Sorry to be particular, but in all of the above results you come out with a load of greater than 32amp.
    It seems that there's a general view that that'll be OK because you've put plenty of 8.5kW showers on 32 amp mcb's over the years and never had any problems at all.
    A teenage girl in a shower will strain the close margin installation, leaving a soapy person with no shower.

    My college drilled into us the mantra
    Ib ≤ In ≤ Iz
    and, in a 2391 exam, if you even suggested that it was OK to have Ib > In you'd quite rightly fail. Those bu66ers at C&G deliberately set the questions to have you sit on a fine margin and make a mistake.

    Sorry, it ain't right. 8.5KW is too big for a 32A MCB.
     
  7. robertpstubbs

    robertpstubbs Screwfix Select

    Out of interest, does an MCB operate directly in relation to the current, or is it also affected by voltage?
     
  8. Bazza

    Bazza Screwfix Select

    It knows nothing about voltage.
     
  9. robertpstubbs

    robertpstubbs Screwfix Select

    I once had to drag a fainted woman out of my shower to stop her from drowning. I never got my soap back.
     

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