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Bussman Point by Point AIC Calcs

Bussman Point by Point AIC Calcs

Bussman Point by Point AIC Calcs

(OP)
I've been evaluating the Point by Point method of AIC calcs that is in the Bussman Fuse book and also indicate in other literature.  They have calculation for an f factor and an M factor.  I'm trying to figure out where they come up with the M factor (the multiplying factor) 1/1+f.

RE: Bussman Point by Point AIC Calcs

Think of "M" as the percent (%) of the available fault current that can travel downstream to a given point on the system.

Where f = some function of length, cable type, voltage, and and available fault current at the "beginning" of a system(in many casees this will be available fault current at the secondary of a transformer)

RE: Bussman Point by Point AIC Calcs

Also note that if all other factors are constant (voltage, available SC, cable type) that M decreases exponentially with cable length.  

RE: Bussman Point by Point AIC Calcs

(OP)
Thanks for responding.  I understand the M being a percentage of available fault.  What I'm trying to do is disect these formulas to determine how they were derived.  All items in the f formula I can account for, but I'm not sure why they add 1 to the f and then take the inverse.

RE: Bussman Point by Point AIC Calcs

Interesting...now you've got me thinking about it...For now, I'm going to guess that 1/(1+f) is some kind of approximation for:

exp^-f(x)

where f is some real value of function f(x) and x > 0.  

OR maybe its some kind of approximation for a summing series.  I'll check into later this evening...I'm studying for the FE anyway.  

RE: Bussman Point by Point AIC Calcs

(OP)
Any more thoughts on the derivation of the point-by-point formulas?

RE: Bussman Point by Point AIC Calcs

See thread238-172100 for my opinion.

As for your basic question, ask Bussmann.

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