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Organizing my fuse inventory at the plant I came across some Ware 56-50 Amp (FRS style/size). The world of fuses is complicated enough... I cannot find any info on what this seemingly dual rating is. Anyone
 

Julie.

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Again, I'm not concerned with the Dual Element design/function of the fuse but rather the unusual amperage rating "56-50Amp."
It isn't that unusual, gM motor fuses to bs88 have dual rating, usually specified as say 20M32, this will have a long term tripping characteristic similar to a standard gG fuse of 20A rating, but a shorter time tripping characteristic of a 32A gG fuse.

If you used a standard gG fuse of 20A on the motor, it would provide a reasonable overload protection, but upon start it would likely blow the fuse as the startup current would be too much.

If you used a standard 32A gG fuse, the fuse would allow the start up, but for longer term overloads, it wouldn't provide sufficient protection.

Hence the gM fuses - closer overload protection similar to a 20A gG fuse, and the longer tripping time similar to a 32A gG fuse at higher currents.

This is a older fuse, again dual element like gM fuses but with overload characteristics similar to a 56A fuse, but quick blow at the higher currents similar to a 50A fuse. (The opposite way to the motor fuse)

- basically a compromise characteristic that is something between 56A and 50A
 

DPG

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Organizing my fuse inventory at the plant I came across some Ware 56-50 Amp (FRS style/size). The world of fuses is complicated enough... I cannot find any info on what this seemingly dual rating is. Anyone

'The world of fuses' sounds like a theme park the likes of people on here would go to. Lucien would probably run it. Westward would be telling people which fuses would fit which type of holder.
 
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It isn't that unusual, gM motor fuses to bs88 have dual rating, usually specified as say 20M32, this will have a long term tripping characteristic similar to a standard gG fuse of 20A rating, but a shorter time tripping characteristic of a 32A gG fuse.

If you used a standard gG fuse of 20A on the motor, it would provide a reasonable overload protection, but upon start it would likely blow the fuse as the startup current would be too much.

If you used a standard 32A gG fuse, the fuse would allow the start up, but for longer term overloads, it wouldn't provide sufficient protection.

Hence the gM fuses - closer overload protection similar to a 20A gG fuse, and the longer tripping time similar to a 32A gG fuse at higher currents.

This is a older fuse, again dual element like gM fuses but with overload characteristics similar to a 56A fuse, but quick blow at the higher currents similar to a 50A fuse. (The opposite way to the motor fuse)

- basically a compromise characteristic that is something between 56A and 50A
Interesting, I thought it might be something along the line of compensating for inrush for a short period but just haven't come across these before. Thank you.
 

pc1966

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Here is a data sheet for one of those Eaton fuses:

On page 2 there are the current-time curves and you see the definite kink at around x6 rating where it goes from slow-ish "overload" protection towards quick "fault" protection. As you get towards the bottom of the time plot (i.e. around 10ms with highest current shown) you see the curves flatten very slightly as the fuse reaches the "constant I2t" point with the slope of 2 decades time per decade current (i.e. the square factor).

Those fuses are not cheap (£131.68 each and pack of 5 from Farnell) but they are also rated to break 300kA which is an astonishing fault level. I cannot even begin to consider what sort of a supply would deliver that!

Compared to a MCCB or ACB of similar interrupt capability I suspect those fuses are cheap... Also worth noting that the max I2t energy let-through of those fuses (last page) is around two orders of magnitude less than at typical MCCB.
 
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