L/R ratio

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LMAO

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Texas
Can anyone please explain this L/R ratio? Does L/R ratio affect the voltage rating of a fuse, interrupt rating of a fuse, or both? Does it concern fuses for DC applications only? Or all fuses?
 

ron

Senior Member
From a document by Bill Brown System Protection

static.schneider-electric.us

The time constant of the circuit is (L/R) and thus the higher the value of L/R the longer the transient will last. Instead of (L/R) power systems typically are defined in terms of (X/R), where (X/R) is the ratio of the inductive reactance of the short-circuit impedance to its resistance. Thus the higher (X/R) or the ?X/R ratio,? the longer the short-circuit transient will last. This has great implications on the rating of equipment.

Low voltage fuse AC interrupting ratings are based upon a maximum power factor of .2, corresponding to a maximum X/R ratio of 4.899. In order to evaluate a low voltage fuse?s interrupting rating on a system with a higher X/R ratio the system symmetrical fault current must be multiplied by a multiplying factor
 
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