I went on a troruble call today for a breaker tripping on an outdoor sign. The breaker did not slam like a direct short so upon amping I found that it will hold 60 amps for a couple of seconds. I know that a breaker will hold a large overload for a time due to inverse trip characteristics but could not find any tables in the NEC ( 99 version I believe, it's in the truck and too lazy to go check). I have seen some info on this but can't remember where I found it. Would like to know so I can better explain it to the customer other than , yep they'll hold for a while. Thanks guys.
Ditto resqcapt. You need the info. BTW, I had to troubleshoot a sign fed by an underground conduit that tripped sometimes. When it did, the current rapidly(2-3 seconds) increased from 16-17 amps to 60,70,80,trip. The underground j-box had become exposed and, depending on the weather(dry, damp, or wet ), the breaker would either hold or not. It was interesting that once the current started to flow to ground, it started low, but rapidly increased to the point of tripping . Had to re-feed overhead.
Actually it was a rat's nest. Flush with grade in a used car lot, no cover, exposed wire ends, gravel & dirt filled. Amazed nobody got hurt. The box was so distorted that if I had a cover, it would never fit. Had to kill the whole thing & start over.