Help !! Transformer overcurrent protection

[brother]

Just trying to get a better understanding. Ive read art. 450.3 on the over current protection for transformers, but i remember some where else where I think its 240.4(B) where you can go to the next higher size breaker 800 amps or less. But there was a section that forbid this for transformers. I cant find it, please help. Thanks

 

[iwire]

But there was a section that forbid this for transformers. I cant find it, please help.

Look at the title of table 450.3(B) and notice that "Note 1" only allows rounding up on the 125% ratings not the 250% ratings.

Also look at the last sentence of 240.21(C).

However keep in mind that 240.21(C) has nothing to do with the protection of the transformer, it only deals with protection of the conductors leaving the transformer.