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Determining Max Zs For Time Current Curve

Former Community Member
Former Community Member
How do you determine the max Zs when the manufacturer does not list or specify the maximum permitted earth fault loop impedance? TN system.


https://library.industrialsolutions.abb.com/publibrary/checkout/GES-6119D?TNR=Time%20Current%20Curves%7CGES-6119D%7CPDF&filename=GES6119.pdf
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    If you do not wish to use the BS7671 figure, you can calculate the disconnection time from the manufacturer's worst-case energy let through. However, this is a deviation from BS7671 and needs to be fully documented and noted on the EIC. It is probably not worthwhile unless you are really stuck. The alternative is additional supplementary bonding to reduce R2, or choose a larger cable.
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    If you do not wish to use the BS7671 figure, you can calculate the disconnection time from the manufacturer's worst-case energy let through. However, this is a deviation from BS7671 and needs to be fully documented and noted on the EIC. It is probably not worthwhile unless you are really stuck. The alternative is additional supplementary bonding to reduce R2, or choose a larger cable.
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