power shower rcd ?

Discussion in 'Electricians' Talk' started by bobbybobbob, May 22, 2020 at 12:21 PM.

  1. bobbybobbob

    bobbybobbob New Member

    Noticed the 40amp rcd made a buzzing noise recently whenever the 7kw power shower went on. Then a few days ago stopped working completely, no power at all to the switch.
    Bought a new rcd, replaced it in the MK16th addition fuse board, tried the shower, worked great. Well for 5 minutes! Then has stopped working again. What could be causing rcds to blow? RCD have never tripped btw
     
  2. MGW

    MGW Screwfix Select

    A power shower at 7 kW would blow you into next week, so what do you really have? If you get the instant shower mixed up with power shower what else is wrong? I would guess nothing wrong with the RCD if it is a RCD more likely some thing wrong with the shower, but in a 16th Edition fuse board would expect to find a 83A RCD and a 40A MCB so what is actually tripping.
     
  3. bobbybobbob

    bobbybobbob New Member

    7kw triton electric shower has been in the property and worked perfectly every day for the last 3 or 4 years. On the fuse board there is a bunch on rcd or mcb, (i don't know the difference), for downstairs sockets, upstairs lights, downstairs lights, upstairs sockets, garage. Then a separate one 40a just for the shower only. This 40a shower mcb has recently been making buzzing sound until few days ago shower stopped working, no power getting even to the pull switch that turns the shower and light on / off. The mcb never once tripped. I changed the mcb for a new one. Instantly the shower started working again, but within a day, again WITHOUT the mcb tripping, the shower is no longer getting power, again no power to the switch outside the shower that turns it and the light in the shower on / off. I don't think there is a problem with the shower I think it somewhere else. What would cause a mcb to blow opposed to trip?
     
  4. Comlec

    Comlec Screwfix Select

    An MCB operates (opens the circuit) when one of two conditions are present
    Overload - if the current being drawn is in excess of the MCB rating
    Short Circuit - a connection is made directly between the Live and Neutral or Earth in the circuit

    If you are beginning to feel this is beyond your skill to resolve then time to call in a registered electrician.
     
    Teki likes this.
  5. terrymac

    terrymac Screwfix Select

    What test instrument are you using to establish there is no power to the switch ? Is switch ceiling mounted , pull cord type ?
     
  6. bobbybobbob

    bobbybobbob New Member

    I am pretty capable, code daily for a living, python, C++, java, ajax. I fully get conditional / statements.
    I'm convinced it's not an overload as nothing is tripping but RE short circuit, could this mean a grounding issue and if so what tests would you'd recommend for finding the culprit short?
     
  7. bobbybobbob

    bobbybobbob New Member

    Fluke multimeter, set range at 250v, the switch is dead from fuse board. Have ohm tested each L N E by joining each at one end then completing the circuit at the fuse board end using the multimeter set to ohms, no breaks. Cable is good.
    Yes switch is a ceiling mounted pull cord type ?
     
  8. Teki

    Teki Active Member

    Do you operate the shower isolator pull-cord switch often?

    Have you tested for voltage either side of the switch terminals with the switch in the on position?
     
  9. terrymac

    terrymac Screwfix Select

    I am confused ,are you saying the MCB that is new ,does not energise the circuit when it's switched on ?
     
  10. bobbybobbob

    bobbybobbob New Member

    Is there a test you can run on the MCBs
    yes, the switch is fine not faulty. Tested cable from fuse board and switch, all good.

    The problem is no power out of the mcb 40a. Something somewhere is killing the mcb. If I switch it for a spare mcb the shower will work fine for a day and then this new mcb will somehow blow (not trip) mcb will completely stop working.
     
    terrymac likes this.
  11. bobbybobbob

    bobbybobbob New Member

    Yep brand new MCB, worked for one day, then no longer working. Is there a logical test I can do on the mcb to test to see if its truly broken or if the fault lies elsewhere?
     
    terrymac likes this.
  12. Teki

    Teki Active Member

    Disconnect the outgoing cable to the shower from the MCB and test if there is a voltage on the output of the MCB with it switched on. What was the condition of the bus bar tab when you replaced the MCB?
     
  13. bobbybobbob

    bobbybobbob New Member

    Only way I can think of testing the mcb is to take it out then somehow generate a current or a load which is then placed across the mcb to see what happens
     
  14. bobbybobbob

    bobbybobbob New Member

    ok will do this thankyou. bus bar was mint copper. Looked like new, think its called a floating bus bar. The mcb were all screwed extremely tightly to it
     
  15. unphased

    unphased Screwfix Select

    If there is no voltage after the mcb have you checked that the busbar is tightly clamped in the main switch terminal AND it is correctly seated in the main switch terminal not clamped skew whiff. Also, the neutral is correctly and tightly terminated in the neutral bar. Can you post a pic of the section of the CU with the front cover removed?
     
  16. bobbybobbob

    bobbybobbob New Member

    thanks man, mcb seems fine 259v coming out the mcb. So I got to start hunting for a gremlin somewhere
     
  17. bobbybobbob

    bobbybobbob New Member

    so yes we have voltage out of the mcb. Problems must be elsewhere
     
  18. unphased

    unphased Screwfix Select

    Then it is probably a neutral fault if you have voltage on the outgoing side of the mcb. Check the neutral wire in the CU carefully to make sure the insulation isn't fouling on the terminal and it is tightly terminated.
     
  19. terrymac

    terrymac Screwfix Select

    Please check the voltages at the switch
    Live to neutral ,and live to earth.
    If cables are ok and MCB has + 250v,
    Then the switch is suspect ,as is the neutrals integrity.
     
  20. unphased

    unphased Screwfix Select

    I must admit, 99% of shower issues are caused by the shower pull-cord switch burning out. One loose termination and it buggers up the circuit.
     
    WillyEckerslike and terrymac like this.

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