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Amtech Software Update Zs Calculation Issues.

Kieran Small

Has anyone encountered an issue arising from an Amtech software update issued September 2025 which has changed how they calculate Zs of a circuit in line with IET guidance that came out in 2022? The change mainly effects cables run in parallel over longer distances

If so, has anyone found a way to alter cables which has previously passing Zs values but are now exceeding the max permitted Zs to bring the Zs value back to acceptable limits short of total infrastructure redesign? Or has anyone had any guidance from the IET on how this update can be handled for legacy projects where cable calculations have already been completed and the project is being built on site but changes to design during construction are required?

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    Kieran Small said:
    Amtech software update issued September 2025 which has changed how they calculate Zs of a circuit

    Is this actually a subtle bug fix and all previous calculations in some particular "special case" (aye, right) were slightly incorrect?

    Maybe the apparent regulation update (have they stated which reg?) was actually a clarification, and made plain the method of calculation and the previous software geeks had misunderstood?

    In 'big company' software it's quite easy for the code implementation be no where near those who actually understand what is being calculated, so the coder may have misunderstood what the wording says.

    I heard a story of a rotary angle encoder being fed to the sine/cosine formulae without any appreciation that the encoded angle was in fractions of a revolution, rather than radians. SI was the standard, so the encoder must produce radians, obviously. Similar misunderstanding happen all over the place. You could have 'cross section' being interpreted as area in one place and diameter in another and gauge in a third.

  • 0 in reply to Philip Oakley

    So Google AI to the "rescue" ? >lmgtfy "Amtech group Zs software calculation bug fix"

    > Amtech software suite, has released several updates over the years addressing various calculation issues, including those potentially affecting Zs values

    Specific bugs fixed related to Zs calculations in past releases include:

    • Incorrect k value: A bug was fixed where certain 300mm cables were obtaining an incorrect k value from regulatory tables used for calculations.
    • Adjustable RCDs: A bug was resolved where changing the Earth Fault settings on an adjustable RCD did not correctly update the maximum Zs figure in the software.
    • Adiabatic calculation time: A bug was fixed where the errors and warnings dialog displayed an incorrect disconnection time used for the Adiabatic calculation. 

    <

    So, some possibilities.

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  • 0 in reply to Philip Oakley

    So Google AI to the "rescue" ? >lmgtfy "Amtech group Zs software calculation bug fix"

    > Amtech software suite, has released several updates over the years addressing various calculation issues, including those potentially affecting Zs values

    Specific bugs fixed related to Zs calculations in past releases include:

    • Incorrect k value: A bug was fixed where certain 300mm cables were obtaining an incorrect k value from regulatory tables used for calculations.
    • Adjustable RCDs: A bug was resolved where changing the Earth Fault settings on an adjustable RCD did not correctly update the maximum Zs figure in the software.
    • Adiabatic calculation time: A bug was fixed where the errors and warnings dialog displayed an incorrect disconnection time used for the Adiabatic calculation. 

    <

    So, some possibilities.

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