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MCB & Cable Size for 3 Phase Star (Wye) with Neutral

Nano Brewery
Hi, I'm trying to understand/figure out what MCB & Cable Size would be required for a 3 Phase 9kW Immersion Element wired in Star using Neutral?  I have been a little confused by the results when using various online calculators. One example here: https://www.watlow.com/resources-and-support/engineering-tools/3phase-delta-wye-calculator

i.e. Using a Line Voltage of 400V equals a Phase & Line Current of 12.99A.  Where as using a Phase Voltage of 230V equals a Phase & Line Current of 22.59A?


My questions are:

1. Are these calculations correct?

2. What Amperage MCB would be required?

3. Would the MCB required need to be 3P, 3P+N or 4P?

3. Would 1.5mm2 cable at a 6 meter run be adequate?


Thanks in advance for your feedback and help.
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    broadgage:

    Yes, in the example given the line current will be about 13 amps. The exact calculated value will depend on whether 230 volts or 240 volts is assumed. The actual measured value will depend on mains voltage fluctuations and on manufacturing tolerances of the elements, what will be about 13 amps.


    A 16 amp or a 20 amp MCB would be fine. I would prefer 20 amps because under worst case conditions the load current might be  about 15 amps if the "3000 watt" elements were actually 3,150 watts due to manufacturing tolerances, and if they are designed for 230 volts and if the actual voltage was 250 volts.




    Cheers.  Assuming I went for the 20A MCB, would I then need a 32A Socket/Rotary Isolator?  Or would a 16A Socket/Rotary Isolator be suitable?


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  • 0
    broadgage:

    Yes, in the example given the line current will be about 13 amps. The exact calculated value will depend on whether 230 volts or 240 volts is assumed. The actual measured value will depend on mains voltage fluctuations and on manufacturing tolerances of the elements, what will be about 13 amps.


    A 16 amp or a 20 amp MCB would be fine. I would prefer 20 amps because under worst case conditions the load current might be  about 15 amps if the "3000 watt" elements were actually 3,150 watts due to manufacturing tolerances, and if they are designed for 230 volts and if the actual voltage was 250 volts.




    Cheers.  Assuming I went for the 20A MCB, would I then need a 32A Socket/Rotary Isolator?  Or would a 16A Socket/Rotary Isolator be suitable?


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