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M.E.M. R.C.D. Tripping Off.

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Mornin' All,

                      on this mild still spring type morn.

Do you remember the M.E.M. type R.C.D. that had a three position switch?


TOP POSITION = ON,


MID POSITION = TRIPPED.       LOWEST POSITION = PUSH SWITCH DOWN FROM MID POSITION BEFORE PUSHING TO TOP POSITION TO RESET TO ON.


Many months back I had a problem that when the customer turned her oven OFF it tripped the R.C.D. to OFF. (Read that carefully).


A new R.C.D. seemed to solve the problem.


Last week I came across exactly the same problem. Now that  a new R.C.B.O. consumer unit has been installed all is o.k.


Any ideas as to why this situation exists?


Z.


  • Former Community Member
    0 Former Community Member
    Any ideas as to why this situation exists?


    Quite probably for those who have read the instructions, as a means to differentiate between detecting an overcurrent or RCD trip. 


    Regards


    BOD
  • 0
    Following on from BOD, it also means that the Device cannot be immediately reclosed, without the deliberate action of moving the operating lever to the “Off” position first. There are (were) a few other manufacturers that used the same method. 


    There is also an interesting issue with RCBOs on TT. If you fit a 10 way RCBO with an ordinary main switch, worst case, you can have up to 300mA of leakage before you get a trip. Your earth needs to be good enough for this, but ideally you want a time delayed main switch, especially if the RCBOs are single pole switching. 


    Regards,


    Alan.
  • 0
    And the reason for the R.C.D. tripping off when the oven is turned off is......?


    Z.
  • 0
    Alan Capon:

    Following on from BOD, it also means that the Device cannot be immediately reclosed, without the deliberate action of moving the operating lever to the “Off” position first. There are (were) a few other manufacturers that used the same method. 


    There is also an interesting issue with RCBOs on TT. If you fit a 10 way RCBO with an ordinary main switch, worst case, you can have up to 300mA of leakage before you get a trip. Your earth needs to be good enough for this, but ideally you want a time delayed main switch, especially if the RCBOs are single pole switching. 


    Regards,


    Alan. 


    Ideally upfront 100mA time delay RCD and then DP RCBO’s 


  • Former Community Member
    0 Former Community Member
    customer turned her oven OFF it tripped the R.C.D. to OFF


    A little more detail required. 


    What does the oven thermostat switch?

    Turning the oven off. How? By the temperature control switch? By the associated appliance switch. Is it part of a stand alone cooker?


    Regards


    BOD
  • 0
    And the reason for the R.C.D. tripping off when the oven is turned off is......?

    First guess would be DP switching, a high impedance N-PE fault on the oven and the DP switch happens to open N momentarily before L. Normally N is held close to 0V so little current escapes through the fault (not enough to trip the RCD), but when N is opened and L is still connected, the load's N is pulled up towards L voltage by the connected load and so a much larger current escapes - hence the RCD trips.


       - Andy.
  • 0
    perspicacious:
    customer turned her oven OFF it tripped the R.C.D. to OFF


    A little more detail required. 


    What does the oven thermostat switch?

    Turning the oven off. How? By the temperature control switch? By the associated appliance switch. Is it part of a stand alone cooker?


    Regards


    BOD


    First case. The temperature control switch did cause the oven to trip the R.C.D. to the tripped position. I witnessed this happen, but it did not trip the R.C.D. every time, just occasionally. I believe that the first appliance was a stand alone cooker, the second more recent one was just an oven on its own, and the temperature control switch caused the problem.


    Z.


  • Former Community Member
    0 Former Community Member
    You might find that some appliances very often switch the neutral...........


    Regards


    BOD

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