Overload Ability of Power Fuses

[mbrooke]

What does overloading do to power fuses? For example, a 300E fuse has a pickup of around 660 amps. I'd like to have 6 hours of 330 amps loading during contingency switching. This still leaves my with 200% for short load time inrush.

 

[Hv&Lv]

I‘m not going to look at the curve to see any times...
but short answer is it weakens them.
doing this continually eventually get the fuse weak enough that it won’t hold its characteristics any longer.
fuse manuf. call this “sneak out”

 

[mbrooke]

I‘m not going to look at the curve to see any times...
but short answer is it weakens them.
doing this continually eventually get the fuse weak enough that it won’t hold its characteristics any longer.
fuse manuf. call this “sneak out”

S&C hints that it won't with their SM and SMU fuses- but chances are it be the case.

Another thing I've read is that it shifts the whole time current curve...

 

[Hv&Lv]

S&C hints that it won't with their SM and SMU fuses- but chances are it be the case.

Another thing I've read is that it shifts the whole time current curve...

If it weakens it, it has to shift it and reconfigure the curve..

 

[mbrooke]

If it weakens it, it has to shift it and reconfigure the curve..

Even if it doesn't weaken it, the heat alone can still shift the curve?

Overloading with either type of element construction can result in loss of coordination with other protective devices because all published melting time-current characteristic curves are based on no preloading. The excessive preloading produced by overloading in accordance with the values listed in Tables 1 through 8 causes a reduction in melting time by as much as 70% of the published values.

https://www.sandc.com/globalassets/sac-electric/documents/sharepoint/documents---all-documents/information-bulletin-352-190.pdf?dt=637201381771041893

 

[Hv&Lv]

Any overloading which causes annealing in the silver or other fuse metals will shift the curve

 

[mbrooke]

Any overloading which causes annealing in the silver or other fuse metals will shift the curve

Got it!

Guess I'm limited to the values here:

https://www.sandc.com/globalassets/sac-electric/documents/sharepoint/documents---all-documents/information-bulletin-242-190.pdf?dt=637201464078109714

I get a daily 1 hour allowance of 330 amps on the SM-5

This stays between you and me, but I'm only loading feeders to 50% of normal peak

 

[Besoeker3]

What does overloading do to power fuses? For example, a 300E fuse has a pickup of around 660 amps. I'd like to have 6 hours of 330 amps loading during contingency switching. This still leaves my with 200% for short load time inrush.

Most mainstream manufacturers give I2t curves