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RCBO Issues

AlexG

I have a wylex split consumer unit with two WRS80/2 30mA RCDs feeding a series of final circuits including ring mains and lighting. These are fed by NHXB32 and NHXB6 MCBs respectively. Currebt system works fine and there are no earth faults on the system. 

I have fitted RCBOs in place of the MXCBs as follows:

  • NHXSBS6B on the lighting
  • NHXSBS32B on the ring mains
  • In place of the WRS80/2s I have fitted WRDMT100/2 time delayed RCDs for discrimination. 

Ring main RCBOs work fine. The RCBO on the lighting circuits trip immediately I switch the breaker on. This happens on all three lighting circuits. 

  • Lighting circuits have a mix of LED and halogen lamps. Total LED load on each is around 120W (12x6W)
  • Each RCBO is wired correctly and the correct meutrals are wired into the RCBO. The neutral flying lead is on the neutral bar and the functional earth is connected to the earth bar. 

Can anyone suggest why the RCBO is tripping? My only suggestio wuld be a borrowed neutral. Given all three lighting circuits use the same neutral bar and the problem has only arisen since I fitted RCBOs then I'm wondering if neutrals have been shared between circuits (would not have been an isue before as all three circuits shared the same WRS80/2 RCDs. 

Thanks in advance 

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    My only suggestio wuld be a borrowed neutral.

    That was my 1st guess too - a common 'trick of the trade' of yore was to drop a twin & earth to the hall light switch, bridge com on that com on the landing switch and run another twin & earth as "strappers" to the landing light switch.Nett result the landing light was connected to upstairs N and downstairs L. Wall lights were another common one, but they tended to be connected to the socket circuit N, which would probably have shown up with the ring RCBOs tripping as well.

    2nd/3rd guesses would involve some incompatibility with the loads (e.g. LED ballasts) or switch-on surges tripping the magnetic part of the circuit breaker (try with all the lights switched off and see if the RCBO distinguishes between overload and residual trips - some trip to a centre position for residual), Failing that perhaps a bad batch of RCBOs - try the RCBO with its output disconnected.

       - Andy.

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  • 0

    My only suggestio wuld be a borrowed neutral.

    That was my 1st guess too - a common 'trick of the trade' of yore was to drop a twin & earth to the hall light switch, bridge com on that com on the landing switch and run another twin & earth as "strappers" to the landing light switch.Nett result the landing light was connected to upstairs N and downstairs L. Wall lights were another common one, but they tended to be connected to the socket circuit N, which would probably have shown up with the ring RCBOs tripping as well.

    2nd/3rd guesses would involve some incompatibility with the loads (e.g. LED ballasts) or switch-on surges tripping the magnetic part of the circuit breaker (try with all the lights switched off and see if the RCBO distinguishes between overload and residual trips - some trip to a centre position for residual), Failing that perhaps a bad batch of RCBOs - try the RCBO with its output disconnected.

       - Andy.

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