800 AF breaker

[Prototype1]

Hey guys, I am trying to find a next breaker size. The transformer is 15KVA, 480 V, 3 phase. The Breaker is 800 AF (500 mcm) 380*2 = 760 A. ampacity of the main breaker, which is 100 Amps in this case. The fault current is 534 A. I need to know how to find the next breaker size, grounding, conductor size. I went to Article 240.4. and it saying the "ampacity of conductors it protects shall be equal or greater than the rating of the overcurrent device defined in 240.6".

I know to find conductor size. You got article 430.16 - and table 310.16. But in this I don't what amps I need to use to multpily by FLC =1.25* # = .
For Ground, we need to go to table 259.122 and find the AWG.
After that you are going to Ch 9 table 5, table 1 ( 40%), table 4. To find the trade size.

I want to how to size the next breaker size that is connect to 800 AF breaker. I am confuse.

 

[augie47]

Are you asking for the next breaker larger than 800 amp or the breaker size for your 15kva transformer ?
A 15kva transformer with primary protection would be a 25 amp breaker.

 

[electrofelon]

Hey guys, I am trying to find a next breaker size. The transformer is 15KVA, 480 V, 3 phase. The Breaker is 800 AF (500 mcm) 380*2 = 760 A. ampacity of the main breaker, which is 100 Amps in this case. The fault current is 534 A. I need to know how to find the next breaker size, grounding, conductor size. I went to Article 240.4. and it saying the "ampacity of conductors it protects shall be equal or greater than the rating of the overcurrent device defined in 240.6".

I know to find conductor size. You got article 430.16 - and table 310.16. But in this I don't what amps I need to use to multpily by FLC =1.25* # = .
For Ground, we need to go to table 259.122 and find the AWG.
After that you are going to Ch 9 table 5, table 1 ( 40%), table 4. To find the trade size.

I want to how to size the next breaker size that is connect to 800 AF breaker. I am confuse.

Your post is so hard to to follow and makes almost no sense. Sorry not trying to mean, just letting you know I have no clue what you have going on.

 

[jim dungar]

When the NEC says next size larger breaker it is simply allowing you to round up your breaker requirements to the next standard NEC rating.
For example: your conductors have a an ampacity of 760A which is not a standard value, so you can chose an 800A instead because this is the next larger size.

To simplify your design you should start with your loads, first choosing the branch circuit conductors and protection. Then work on the feeders ending at your source.

 

[Prototype1]

Are you asking for the next breaker larger than 800 amp or the breaker size for your 15kva transformer ?
A 15kva transformer with primary protection would be a 25 amp breaker.

Breaker size for the 15kva transformer. Sorry, I just read it too, and it was confusing for me too. My bad.

The question I have is how to size a generator and conductor, conduit size?
I know to find conductor size. You got article 430.16 - and table 310.16.
For Ground, we need to go to table 259.122 and find the AWG.
After that you are going to Ch 9 table 5, table 1 (40%), table 4. To find the trade size.

I want to if I am doing it right. How I should size the generator now? Can you give sections and steps to size the generator?

 

[Prototype1]

Your post is so hard to to follow and makes almost no sense. Sorry not trying to mean, just letting you know I have no clue what you have going on.

My bad, I did not know how to explain it properly. I overthink it. I want to know how to size the generator, conductor, conduit size. Likewise, I am still bad at reading NEC and following steps to size it.

 

[electrofelon]

My bad, I did not know how to explain it properly. I overthink it. I want to know how to size the generator, conductor, conduit size. Likewise, I am still bad at reading NEC and following steps to size it.

So what is the relationship between the 15 KVA transformer, the 800 amp breaker, and the generator? What are you trying to power with the generator?