Overcurrent protection 45 kva transformer

[cjact]

Blue prints requires a 100 amp 3 phase 120/208 panel. Blueprint has no detail to feeder size and wire sizes. i know i can feed a 45 kva with 480 3 phase and a 70 amp breaker and get 125 amps secondary. So the secondary panel has a 100 amp main breaker . I fed a 45 kva transformer with #6 thwn from a 480 volt panel with a 60 amp 3 phase breaker. 2 ft from the transformer i placed my secondary panel i fed the 100 amp secondary panel with #3 thwn . Being that my 100 amp panel can exceed 100 amps due to the main breaker is safe to say i do not have to rate the entire transformer capacity at 125% of the true value and capacity that a 45 kva transformer can handle. if this is a correct configuration i would i then bond my XO to building steel based on the the #3 conductors of the secondary side of my transformer. It has been a while since i have installed transformers with out an engineer dictating the parameters (which are usually overkill).

 

[electrofelon]

Blue prints requires a 100 amp 3 phase 120/208 panel. Blueprint has no detail to feeder size and wire sizes. i know i can feed a 45 kva with 480 3 phase and a 70 amp breaker and get 125 amps secondary. So the secondary panel has a 100 amp main breaker . I fed a 45 kva transformer with #6 thwn from a 480 volt panel with a 60 amp 3 phase breaker. 2 ft from the transformer i placed my secondary panel i fed the 100 amp secondary panel with #3 thwn . Being that my 100 amp panel can exceed 100 amps due to the main breaker is safe to say i do not have to rate the entire transformer capacity at 125% of the true value and capacity that a 45 kva transformer can handle. if this is a correct configuration i would i then bond my XO to building steel based on the the #3 conductors of the secondary side of my transformer. It has been a while since i have installed transformers with out an engineer dictating the parameters (which are usually overkill).

For a brush up, look at the following:

1. 450.3(B) for transformer protection rquirements. Dont forget this is just for the transformer itself.
2. See 240.21(C) for the transformer secondary conductors.
3. Dont forget 408.36, but if you have a main breaker, that will be covered.
4. 250.30 for grounding.