100 % Rated Fuses

[Vica1ME]

100% rated circuit breakers are often used in large sizes to allow forconductors to be sized smaller than for 80% rated breaker. I amoccasionally asked if we can use 100% rated fuses, but understand that fusibleswitch enclosures are manufactured with only enough inside area to allow fusesto be used at 80%. Are you aware of any manufacturers who have or wouldmake a larger enclosure so that fuses can be used at 100%?

 

[kwired]

100% rated circuit breakers are often used in large sizes to allow forconductors to be sized smaller than for 80% rated breaker. I amoccasionally asked if we can use 100% rated fuses, but understand that fusibleswitch enclosures are manufactured with only enough inside area to allow fusesto be used at 80%. Are you aware of any manufacturers who have or wouldmake a larger enclosure so that fuses can be used at 100%?

I would guess if there is such a thing it is the fuse holder more so then the fuse itself that is going to be designed differently to achieve that rating.

 

[ron]

I have not seen a regular fusible switch rated for more than 80% of fuse size for non-motor loads.

I wouldn't be surprised, if you spec'ed a specialty switch, such as bolted contact switch from Boltswitch or Pringle, that they may have a 100% model.

Fuses would be the same http://www.cooperindustries.com/con...se_Operation_at_100_Percent_Rated_Current.pdf

 

[jim dungar]

I wouldn't be surprised, if you spec'ed a specialty switch, such as bolted contact switch from Boltswitch or Pringle, that they may have a 100% model.

:thumbsup:

 

[310 BLAZE IT]

I would not be fast to specify a 1600a with gfci and 100 percent rated. I was told by multiple vendors that this cannot be made. The fuse and switch must be combination listed at 100 percent which is difficult to get a manufacturer to agree to

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[jim dungar]

The fuse and switch must be combination listed at 100 percent which is difficult to get a manufacturer to agree to...

That may be for a single stand aloneenclosed switch (e.g. 24"w x 36"h x 16"d), but if the switch is mounted into a large switchboard style enclosure (e.g. 36"w 92"h x 24"d) it is not as difficult. Instead of Pringle and Bolt-Switch try Square D, GE, or Eaton.

 

[Jraef]

Just to be clear, it's not the fuse, it's what the fuse is connected to. ALL fuses are tested and listed at 100% of their rating at a minimum, 600A and up (Class L and T) are actually tested and listed at 110%. So if you find a switch rated for 100% continuous (and terminals rated for 90C) the fuses can be used at 100%.

 

[310 BLAZE IT]

Just to be clear, it's not the fuse, it's what the fuse is connected to. ALL fuses are tested and listed at 100% of their rating at a minimum, 600A and up (Class L and T) are actually tested and listed at 110%. So if you find a switch rated for 100% continuous (and terminals rated for 90C) the fuses can be used at 100%.

How do you know this? Is this within a UL document somewhere? And where does it say 100 percent rating? I've never seen this before on any switch.

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[310 BLAZE IT]

Just to be clear, it's not the fuse, it's what the fuse is connected to. ALL fuses are tested and listed at 100% of their rating at a minimum, 600A and up (Class L and T) are actually tested and listed at 110%. So if you find a switch rated for 100% continuous (and terminals rated for 90C) the fuses can be used at 100%.

I got a siemens whitepaper which elaborates on this a little:

 

[Jraef]

Side issue that occurred to me on this. As far as the switch goes, the switch and fuse holders themselves only come in certain sizes. So if you have a 1200A switch and install 900A fuses, that switch can handle 100% of the 900A, because it's really designed for 80% of 1200A (960A).

You still have the issue of the terminations being rated for 90C (at both ends) if you want to use 90C conductors to reduce the size, this was just something I thought of with regard to fused switches vs breakers. Breakers have frame sizes too, and the contacts are always the same as the frame size (except 100A and under) but because a breaker has the trip sensing elements in it based on the rated amps, that's where the limit is.

 

[310 BLAZE IT]

Good point. Your mentioning of 90c has got me searching for terminal ratings now... Is a mlo panel board or fused switch a 90C terminal ever (or can it accept one?) I wish there were an easy way to find temperature ratings of terminals based on equipment types

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[Smart $]

Good point. Your mentioning of 90c has got me searching for terminal ratings now... Is a mlo panel board or fused switch a 90C terminal ever (or can it accept one?) I wish there were an easy way to find temperature ratings of terminals based on equipment types

It has been stated here in the forum that there is currently no LV equipment tested for greater than 75°C operation as part of the listing standard.

Using 90°C rated wire is part of the listing requirement for 100%-rated equipment and you still have to use it at the 75°C ampacity.