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Type T Fuse-Fuse Coordination --- 75% Rule

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bwen08

Electrical
Oct 7, 2010
28
With "T" link fuses, Kearney, Chance, and others all have their charts showing the maximum fault current that various fuse amperes coordinate up to. I understand the 75% rule attempts to take into account preloading, damaged fuses and link temperature. My searching so far has failed to lead me to understanding where this value of 75% originated from, so perhaps someone older/wiser than myself can provide a source where this value is determined.

Along those lines, is anyone else using a different value for a derating factor for the minimum melt/total clear curves intersection and perhaps could you share the reasoning for why it is used?
 
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