Discussion
A fuse wire has 3 copper strands each of 35 SWG and 5A fuse rating. Assuming a paralleling factor of 0.8, determine the overall current rating of the fuse wire.
Answer: C
A fuse made of several strands in parallel does not carry the full sum of the strand ratings, because of the effect of heating of neighbouring strands, and the paralleling factor takes this into account.
\[ I = 3 \times 5 \times 0.8 = 12\ \mathrm{A} \]
So the overall current rating is 12 A, option (C). The value 15 A would be the rating without the paralleling factor, and 22 A and 8.3 A do not follow from the data. The paralleling factor is less than one because the strands do not share the current equally, and so the total is less than the sum of the ratings.
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