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Fault current at a transformer's terminals is full load current divided by the per-unit impedance, so a 4.5% transformer gives roughly 22 times full load current. Cable impedance between the transformer and the fault reduces it, which is why the highest prospective fault current is always closest to the source.
Prospective fault current
Isc at terminals = FLC / (Z% / 100); adding cable impedance reduces it downstream
Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.
Every protective device has a breaking capacity. If the prospective fault current exceeds it, the device can fail explosively instead of clearing the fault.
At the transformer secondary terminals. It falls with distance as cable impedance accumulates, which is why remote sub-boards can use lower-rated devices.