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What are the chances of this ?

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  • 29-07-2015 2:18pm
    #1
    dodzy
    Registered Users Posts: 10,025 ✭✭✭✭


    Friend next door popped in. Shower was nor working. Went in and checked the CU. RCBO was tripped. Failed to reset. Went upstairs to bathroom. Pull-chord switch not working. Not uncommon, I know. (The build quality if these seems to be p**s poor over recent years). Anyway, I was assuming that it was stuck in the ON position at this point. Disconnected supply L & N terminals at the isolator. RCBO still not resetting. Switch had absolutely no resistance when pushing up. Killed power to CU. RCBO still not setting. Thats it so, I thought.

    Got a new 40A RCBO and new isolator switch and installed both. Switched on power and tried shower. RCBO trips after about 10 secs! Switched off shower (Triton T90z) via power button on shower panel. Reset RCBO. Power light on shower illuminates. Hit the power button and bang. RCBO off again. Left power off and removed shower cover. Black sooty deposits everywhere. Cover off. RCBO on. Triton power light illuminated. 240V at terminal. Turn on shower and bang. Trips RCBO. How could you develop 3 faults (the isolator was defunct for some time I'd guess ) ?


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    #2
    brightspark
    Registered Users Posts: 2,637 ✭✭✭brightspark


    At a guess, I'd say the shower damaged the RCBO when it failed initially. Also did you test the isolator with a meter to check if it was switching or not?

    (I recently had a brass dimmer switch short itself to earth and afterwards the MCB would not reset)


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    #3
    dodzy
    Registered Users Posts: 10,025 ✭✭✭✭dodzy


    brightspark wrote: »
    At a guess, I'd say the shower damaged the RCBO when it failed initially. Also did you test the isolator with a meter to check if it was switching or not?

    (I recently had a brass dimmer switch short itself to earth and afterwards the MCB would not reset)
    Yep, after the replacement, I metered the load side / supply side of the switch and they were permanently connected; switch was inoperative - stuck in ON position.


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    #4
    brightspark
    Registered Users Posts: 2,637 ✭✭✭brightspark


    As you mentioned earlier the switch may have been faulty for a while, or possibly it's contacts fused together with the fault current.


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    #5
    brightspark
    Registered Users Posts: 2,637 ✭✭✭brightspark


    Referring to your PM, what resistance between N & E do you get with the new isolator in the off position?

    Getting a zero resistance with the isolator and RCBO on doesn't mean anything (apart from proving the neutralising link is present, but that's not relevant to your issue)


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    #6
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Shower probably has earth fault. Adding new rcbo still showing it.

    Inside of showers covered in black deposit is not unusual. It's from brushes of pump motor.


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    #7
    dodzy
    Registered Users Posts: 10,025 ✭✭✭✭dodzy


    Replaced the shower and all is well. Now to try and establish the fault, just for the pig-iron. Would extensive carbon deposits from the brushes ( very heavy around the commutator ) potentially cause the issue ?

    One thing I did notice between the 2 units when I had them side by side. The N/E terminals on the old motor unit gave a reading of approx 16Kohms whereas on the new unit, there was no reading. Reason for this ?
    The elements of both units turned out similar 11.5 & 14ohms respectively when metered.


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