Arc Flash Question

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bcorbin

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I am currently trying my hand at SKM's Power Tools software, and I ran into a little problem. Whenever I place a fused disconnect switch, it only lets me input the rating of the switch as the "protective device", not the fuse rating.

Take a 60-amp switch, for example. Is the difference between a 30-amp fuse in this switch vs. a 60-amp fuse negligible for Arc-flash calculations, given that they are both going to clear very fast under even the smallest arc fault?

That's the only reason I can even imagine the software doing this. I hadn't really given it much thought before...maybe I'm totally wrong. I e-mailed their tech support, and haven't gotten a reply just yet, but figured someone on this forum might give me a more insightful answer regardless.
 
bcorbin said:
I am currently trying my hand at SKM's Power Tools software, and I ran into a little problem. Whenever I place a fused disconnect switch, it only lets me input the rating of the switch as the "protective device", not the fuse rating.

Take a 60-amp switch, for example. Is the difference between a 30-amp fuse in this switch vs. a 60-amp fuse negligible for Arc-flash calculations, given that they are both going to clear very fast under even the smallest arc fault?

That's the only reason I can even imagine the software doing this. I hadn't really given it much thought before...maybe I'm totally wrong. I e-mailed their tech support, and haven't gotten a reply just yet, but figured someone on this forum might give me a more insightful answer regardless.
Click to expand...

You need to place a FUSE as a standard protective device as not a specialty device like a disconnect. When you place the fuse you can choose if it is shown like a fuse only or a fuse and disconnect.

Clearing times of fuses are dependent on the fault current flowing through the fuse, a 1000A fault may not cause a 60A fuse to enter its current limiting range so it will have a time delay.
 
jim dungar said:
When you place the fuse you can choose if it is shown like a fuse only or a fuse and disconnect..
Click to expand...

Hmmm....I can't seem to find the instructions on how to change the way a fuse is displayed. Give me a shove in the right direction? :-?
 
Whoops, I just stumbled across it, Jim. Thanks for pointing that out to me! I would have been forever wondering.
 
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