conant
Stainless
- Joined
- May 13, 2013
- Location
- Shasta County, Ca. USA
I have always been curious about what it really takes to blow a typical 30 amp slow blow fuse for example protecting a 7 1/2 hp motor on 220 3 phase power.
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Time delay fuse amperage surge question
- Thread starter conant
- Start date
- Replies 2
- Views 984
TDegenhart
Diamond
- Joined
- Mar 26, 2011
- Location
- Geneva Illinois USA
You need the time-current curves for the fuse you want to use. This typical document describes how fuses work, how they are rated and applications. Your electrical supply house should be able to get the exact curve for the fuse you have.
http://www1.cooperbussmann.com/pdf/206c94da-cd15-42a7-99ee-f1bfc6f645fd.pdf
Tom
http://www1.cooperbussmann.com/pdf/206c94da-cd15-42a7-99ee-f1bfc6f645fd.pdf
Tom
The curves are available from the manufacturers, they are nearly always on the website. All the product specs generally are.
But fuses differ a lot. There are regular time delay, and there are "current limiting" types. The current limiting ones will interrrupt the current without exceeding a certain amount of peak current, with voltage and available current from the power source up to the max rating of the fuse. Non-current limiting may "let through" an unspecified peak current.
The absolute minimum current depends on how long you wait..... Some fuses are rated to carry their rating forever, to carry 135% of the rating for at least 4 hours, and to open at 200% in a specified short time. Others have different times and current ratings, often still at 135% and 200% of marked rating.
The current also depends on ambient temperature. A fuse works by melting, and the hotter it is to start with, the less energy (and current) it takes to melt it. So it's rated for more current when very cold, and less current if in a rather hot area. Temperature affects both ultimate current, and also time to melt (open).
Just because the fuse is rated at "X" amperes does not mean it will necessarily open in a precise time, or ever, at a slightly higher current. Normally it takes a considerably higher current to melt the fuse.
US and european fuses also differ, US beng rated on carry current, and european on opening current.
Here is a LOT of info on fuses... more than you want, probably.....
http://www.littelfuse.com/~/media/e.../littelfuse_fuseology_selection_guide.pdf.pdf
But fuses differ a lot. There are regular time delay, and there are "current limiting" types. The current limiting ones will interrrupt the current without exceeding a certain amount of peak current, with voltage and available current from the power source up to the max rating of the fuse. Non-current limiting may "let through" an unspecified peak current.
The absolute minimum current depends on how long you wait..... Some fuses are rated to carry their rating forever, to carry 135% of the rating for at least 4 hours, and to open at 200% in a specified short time. Others have different times and current ratings, often still at 135% and 200% of marked rating.
The current also depends on ambient temperature. A fuse works by melting, and the hotter it is to start with, the less energy (and current) it takes to melt it. So it's rated for more current when very cold, and less current if in a rather hot area. Temperature affects both ultimate current, and also time to melt (open).
Just because the fuse is rated at "X" amperes does not mean it will necessarily open in a precise time, or ever, at a slightly higher current. Normally it takes a considerably higher current to melt the fuse.
US and european fuses also differ, US beng rated on carry current, and european on opening current.
Here is a LOT of info on fuses... more than you want, probably.....
http://www.littelfuse.com/~/media/e.../littelfuse_fuseology_selection_guide.pdf.pdf
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