Example: 225 A continuous load * 1.25 = 281 A. Conductors sized at 300 kcmils with 285 A ampacity. Circuit breaker sized at next size up = 300 A.
From 285 A to 300 A, the breaker would never trip. So wouldn't this cause overheating for the conductors?
You have a load of 225A on conductors with an ampacity of 285. Why would the conductors overheat?
The code allows the next size up but does not allow us to load the conductor above its ampacity.
This would be where in the code?
310.15 Ampacities for Conductors Rated 0?2000 Volts.
(A) General.
(1) Tables or Engineering Supervision. Ampacities for
conductors shall be permitted to be determined by tables as
provided in 310.15(B) or under engineering supervision, as
provided in 310.15(C).
Good point, I was thinking of the 1.25 factor. But if I replace 225A and say 281 A of non continuous load, then this is what I mean by my example.
The code allows the next size up but does not allow us to load the conductor above its ampacity.
This would be where in the code?
Good point, I was thinking of the 1.25 factor. But if I replace 225A and say 281 A of non continuous load, then this is what I mean by my example.
Then you have a load of 281A on conductors with an ampacity of 285. Same question - why would the conductors overheat?
Then you have a load of 281A on conductors with an ampacity of 285. Same question - why would the conductors overheat?"
Good point, I was thinking of the 1.25 factor. But if I replace 225A and say 281 A of non continuous load, then this is what I mean by my example.
This would be where in the code?
Safety factor make sense too.
Take a look at 240.4 (B)
The ampacity tables are on the conservative side. It is very unlikely that the cable would be damaged by running at 400 amps. Keep in mind that the UL standard for OCPDs would permit that 400 amp device to supply 536 amps into the circuit forever without tripping....
My concern is that a load can be designed for 380 A. But, lets say the feeder circuit is fully loaded to that 380A, and then let's say a copier, printer, and fax machine is installed and now the feeder current is 395 A. The 400 A overcurrent device doesn't protect the feeder.
My concern is that a load can be designed for 380 A. But, lets say the feeder circuit is fully loaded to that 380A, and then let's say a copier, printer, and fax machine is installed and now the feeder current is 395 A. The 400 A overcurrent device doesn't protect the feeder.
The ampacity tables are on the conservative side. It is very unlikely that the cable would be damaged by running at 400 amps. Keep in mind that the UL standard for OCPDs would permit that 400 amp device to supply 536 amps into the circuit forever without tripping.
Yes. It has to trip within an hour at 135%, but it is never required to trip at less than 135%. As I understand it, the standard for fuses is the same.You're thinking UL 489, 135% trip test?
ice
As to the 135% thing, I heard, I thought, that a breaker would carry 135% for two hours. Do I have the wrong information?
Then we have this 10,000 RMS Sym. Stuff that is wrote on 15 amp breakers connected to a #14 conductor. Does this mean something?
My understanding is that the breaker must trip in one hour or less at 135% of its rating....As to the 135% thing, I heard, I thought, that a breaker would carry 135% for two hours. Do I have the wrong information?
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My understanding is that the breaker must trip in one hour or less at 135% of its rating.