Install Current Limiting Fuse to Reduce KAIC

MyCleveland said:
Can you ( or anyone ) help steer me towards how to search for these testing standards?
Say "PANELBOARDS" or other item that is NOT an OCPD.
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Go to the UL Web site. The product standards are available there. They are not as easy to get to as you might want but you can search for how to access the standards on Google.
 
jim dungar said:
Really?
That is not what I saw when I built UL508A control panels. There was no blatant acceptance of any upstream CL device unless we specified it.
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Yeah, UL 508a 3rd edition has sections SB4.3.2 (current limiting circuit breakers) and SB4.3.3 (current limiting fuses) that allow the short circuit rating of branch circuit components to be raised to the OCPD rated interrupt current, provided the branch circuit components' rated SCCR is no less than the current limiting OCPD's let-through current. Part (b) of each of these sections goes on to stipulate the branch circuit OCPD will be the limiting SCCR component if it's interrupt rating is less than that of the feeder circuit's current limiting OCPD.
 
Tip DS said:
Yeah, UL 508a 3rd edition has sections SB4.3.2 (current limiting circuit breakers) and SB4.3.3 (current limiting fuses) that allow the short circuit rating of branch circuit components to be raised to the OCPD rated interrupt current, provided the branch circuit components' rated SCCR is no less than the current limiting OCPD's let-through current. Part (b) of each of these sections goes on to stipulate the branch circuit OCPD will be the limiting SCCR component if it's interrupt rating is less than that of the feeder circuit's current limiting OCPD.
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It is not that simple. Read it VERY carefully and parse every word and phrase.

This blessing is related to the let thru current but you still have to use their charts.
 
No, it's pretty simple. Not a lot of ponderous parsing or tea-leaf reading required. Any UL listed or recognized CL OCPD can be used &, you just grab the let-through current values from table SB4.2. Regardless, haggling over the details doesn't change the overarching point, which is that the SCCR of branch circuit components can be raised through the use of a current limiting OCPD in the feeder, but that will not affect the interrupt rating of the branch circuit protective device.
 
jim dungar said:
Yep. Specific fuses, not just any CL fuse you have access to. You cannot use the fuse manufacturers charts.
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And the charts are based on the AFC and the let thru current of the specific class and rating of fuse.

I am not sure but I think the supplement has provision for most if not all classified cl fuses.
 
petersonra said:
And the charts are based on the AFC and the let thru current of the specific class and rating of fuse.

I am not sure but I think the supplement has provision for most if not all classified cl fuses.
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But not all fuses can be used in all circumstances, you must follow the supplement charts for control panels. There may be other charts for other Listed equipment, like HVAC.
 
Did I miss where someone pointed out the virtues of using a transformer to raise SCCR values? They make the 'easy button' look like a challenge, by comparison. LOL
 
jim dungar said:
But not all fuses can be used in all circumstances, you must follow the supplement charts for control panels. There may be other charts for other Listed equipment, like HVAC.
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I think the charts are different for different CL fuses. I rarely use anything but I or CC fuses for such things because they are the most common ones I can use to get higher SCCRs. Plus they are generally less costly and smaller than other options, although class T is smaller but costs more
 
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jim dungar said:
Which are not the ones most ECs would be installing in branch circuit or feeder fusible switches.
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I meant J not I.

I am curious why they would use something other than a class CC or J fuse since they are the smallest and cheapest appropriate fuses and fuse holders available and ECs are notoriously cheap.
 
petersonra said:
I am curious why they would use something other than a class CC or J fuse since they are the smallest and cheapest appropriate fuses and fuse holders available and ECs are notoriously cheap.
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The common, cheap, fusible disconnect/safety switches have clips for Class H/R.
Some maybe ordered with Class J or T clips but they are not commonly available for over the counter sales.
Very very few if any would have provisions for Class CC.
 
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