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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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    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.


    1.5mm cable would in theory be sufficient under ideal conditions, but in practice 2.5mm would be the usual choice to allow for high ambient temperature and for grouping with other conductors.  In practice 4mm might be needed not under the regulations, but for contractual reasons, a common clause in contracts for large installations is "no cables smaller than 4mm to be used for power circuits, and no smaller than 2.5mm for lighting circuits"


    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. 


    A 3 pole MCB would be suitable in most circumstances, but nothing prohibits use of a 3 pole and neutral device or a 4 pole MCB.
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  • 0
    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.


    1.5mm cable would in theory be sufficient under ideal conditions, but in practice 2.5mm would be the usual choice to allow for high ambient temperature and for grouping with other conductors.  In practice 4mm might be needed not under the regulations, but for contractual reasons, a common clause in contracts for large installations is "no cables smaller than 4mm to be used for power circuits, and no smaller than 2.5mm for lighting circuits"


    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. 


    A 3 pole MCB would be suitable in most circumstances, but nothing prohibits use of a 3 pole and neutral device or a 4 pole MCB.
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