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Double pole RCD

MrJack96
Is there anything preventing us from using these type of RCDs for a 55-0-55 circuit?


the picture shows the original set up. And the replacement b27da3454a5814fd623eb7a7fef4edcb-huge-87007dcb-a17d-44db-b7f4-06ceebdf5a1f.jpg

c68f8770359e16551ccee99a957913b2-huge-1935ff0d-6fd0-4eed-9ae1-8224f6776c3a.png
  • 0
    Some RCDs derive a power supply for internal electronics from the LN voltage. Not all of these are suited to a pole to pole voltage of 110 and may not operate, though I suspect most will.


    Given the very short on-line data for the CPR25, the easiest is an Email or  phone call to Contactum UK in the morning - they should know. If they do not, do not use them.

    Technical enquiries



    Tel: 0208 208 7423

    Fax: 0208 438 0281
    technical@contactum.co.uk



    Mike.
  • 0
    I have used a standard 2 pole RCD on a center tapped 110 volt supply as a short term expedient to improve my own safety. 

    I do not believe that such use is compliant with the regulations because the built in test circuit wont work and there is therefore no way for the non technical user to verify operation.


    The test circuit invariably consists of a push button that connects a resistor between one pole of the input and the other pole of the output. The value of the resistor is calculated to pass the nominal trip current at the lowest "normal" mains voltage. Probably to pass 30ma at 217 volts for the common type.

    At 110 volts the test resistance will only pass about 15ma and tripping on pushing the test button is unlikely.

  • 0
    Is an R.C.D. really needed on a 55-0-55 Volt supply as used on construction sites?


    Z.
  • 0
    No, the whole point of RLV (Reduced Low Voltage) is that the credible touch voltage in any significant fault is almost always less than 50V so the safe touch time is 'for ever'. No safety of life speed ADS is needed.


    The slight issue is that some folk like their RLV installation to meet BS7671 when really the whole philosophy of rapid ADS versus safety to touch is quite different. BS 7671 is inspired by a Euro-standard, and generally the non UK authors of the base standard are are not familiar with our 55-0-55 RLV approach, or its 3 phase devilish variant the 66.6-0-66.6 with something like 100-120volts  between two phases 120 degrees apart?. I know it's not normally  66.6 volts really but it does raise eyebrows with my German speaking friends who have been known to call it something that translates to that. As well as muttering about silly island monkeys when they think I'm not listening.

    M.
  • 0
    the picture shows the original set up. And the replacement

    The original seems to be a D1 MCB with a vigi unit attached - in effect an RCBO - just checking that you're only suggesting replacing the RCD element with the RCCB rather than the entire unit.

       - Andy.
  • 0
    AJJewsbury:
    the picture shows the original set up. And the replacement

    The original seems to be a D1 MCB with a vigi unit attached - in effect an RCBO - just checking that you're only suggesting replacing the RCD element with the RCCB rather than the entire unit.

       - Andy.




    I had similar thoughts.


    First off check the original RCBO is suitable, it may not be performing correctly because it is unsuitable for the installation.


    Then if it is suitable, consider replacing like with like.


  • 0
    So it is in theory acting as an RCBO. I’m confused why the original designer would have specified that unit. So functionally it would work under fault?
  • 0
    Zoomup:

    Is an R.C.D. really needed on a 55-0-55 Volt supply as used on construction sites?


    Z.




    In most circumstances, with only 55 volts to earth I would not consider an RCD to be required.

    There are two main exceptions, firstly to tick a box if ones employer, or some other authority says "RCDs to be used on all portable power tools" Without any consideration as to supply voltage or other circumstances.


    Secondly, I would consider an RCD to be a prudent extra precaution in higher risk conditions such as standing in water, or in the rain. The better choice in such cases is often to use compressed air for power tools and LPG or paraffin for lighting.


    55 volts to earth is clearly much less risky than 240 volts, but it is still over twice the limit for SELV, and an RCD could therefore be prudent in high risk situations.

     


  • 0
    these are the replacement I have for the 55-0-55 are we saying the test button still won’t work? 


    CC55936A-58FC-4E87-97D0-76D07D53E2A9.jpegf81d3fba97b9fc73e23ec6b24bc1335a-original-a331d126-18bb-4e30-a87c-200bf649ba27.jpg
  • 0
    I suspect that the test button will not work, unless the makers will confirm otherwise IN WRITING.

    I

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