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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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  • Former Community Member
    0 Former Community Member
    Continue to select a power cable.
    You need to perform the following steps to complete the selection of the preselected cable and the protection device for it:

    - calculate the minimum SC current at the immersion element. The calculated minimum SCC (rms value) allows to verify disconnection time of the MCB.

    - calculate of voltage losses in the power supply line from the transformer to the consumer, taking into account all loads of the feeder.

    - calculate the maximum initial SC current and the peak short-circuit current at the end terminals of the MCB. The calculated maximum SCC (rms and peak values) determines the breaking capacity and the making capacity of circuit breaker.

    05bb7be47c5d5f8caf42b7cd5ee8796d-original-meteorspec4.png

    Of course, the above calculations can be performed only if the parameters of all elements of the supply circuit from the power transformer to the consumer are known.
    f8e23c5d4fa8cb5bf2c8062add2b938e-original-meteorspec6.png


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  • Former Community Member
    0 Former Community Member
    Continue to select a power cable.
    You need to perform the following steps to complete the selection of the preselected cable and the protection device for it:

    - calculate the minimum SC current at the immersion element. The calculated minimum SCC (rms value) allows to verify disconnection time of the MCB.

    - calculate of voltage losses in the power supply line from the transformer to the consumer, taking into account all loads of the feeder.

    - calculate the maximum initial SC current and the peak short-circuit current at the end terminals of the MCB. The calculated maximum SCC (rms and peak values) determines the breaking capacity and the making capacity of circuit breaker.

    05bb7be47c5d5f8caf42b7cd5ee8796d-original-meteorspec4.png

    Of course, the above calculations can be performed only if the parameters of all elements of the supply circuit from the power transformer to the consumer are known.
    f8e23c5d4fa8cb5bf2c8062add2b938e-original-meteorspec6.png


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