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RCBO In Distribution Board or Isolator With RCD?

Nano Brewery
I'm trying to decide which would be the most suitable and sensible option? 


I have a Control Board that will be switching 4x 3-Phase Immersion Elements.

9kW

9kW

6kW

3kW


Control Board has Rail Mount Fuse Holders & Contactors installed for each circuit.


My question is would it be better to have a suitably rated RCBO installed in the Distribution Board which will be feeding the Control Board or should I go with downstream Isolators with RCD's?  I'm leaning towards the later as I would have separate RCD protection on each circuit.


Look forward to your feedback.  Cheers, Dan.

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  • 0
    It depends...


    Firstly, which requirement for RCDs are you attempting to satisfy? (in many situations on a TN system they'd likely not be required at all). Are there any upstream RCDs that you'd need to discriminate with (which might suggest against solid N RCBOs for instance).


    Then what are the operational requirements? Is it acceptable to the user to have all the immersions disconnected if one developed a fault? (if they're all part of the same process that might actually be perfectly acceptable or even desirable, in other situations keeping the others running at all costs might be top of the list).


    Are there any earth leakage (protective conductor) currents to take into account? Mineral insulated elements have a bit of a reputation for being a little leaky, and you have quite an amount of them there. On the other hand spread over three phases the leakage should tend to cancel out .... unless there's any option to switch each phase individually (for reduced output for instance).


       - Andy.
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  • 0
    It depends...


    Firstly, which requirement for RCDs are you attempting to satisfy? (in many situations on a TN system they'd likely not be required at all). Are there any upstream RCDs that you'd need to discriminate with (which might suggest against solid N RCBOs for instance).


    Then what are the operational requirements? Is it acceptable to the user to have all the immersions disconnected if one developed a fault? (if they're all part of the same process that might actually be perfectly acceptable or even desirable, in other situations keeping the others running at all costs might be top of the list).


    Are there any earth leakage (protective conductor) currents to take into account? Mineral insulated elements have a bit of a reputation for being a little leaky, and you have quite an amount of them there. On the other hand spread over three phases the leakage should tend to cancel out .... unless there's any option to switch each phase individually (for reduced output for instance).


       - Andy.
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