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A fuse must carry the load continuously without ageing, so the rating is at least 125% of continuous current, more for high-inrush loads. It must also be no larger than the cable can withstand, since the fuse is what protects the cable rather than the load.
Fuse rating
In >= 1.25 x load current (1.5 x for high inrush) and In <= cable ampacity
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.
Fuse elements age under sustained current near their rating. The 25% margin keeps the element cool enough for a long service life.
The cable. Equipment usually has its own internal protection, but the circuit conductors rely entirely on the upstream device.