30kva secondary breaker sizing

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pushbutton

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On a 30kva Three phase 480 delta ,120/ 208 Y. why would you calculate 83 amps at 208 if most of the circuits being used will be at 120v?
 
It may help if you look at a 208Y/120 30kva 3 phase transformer as (3) 10kva 120v transformers. Same answer 83 amps.
 
pushbutton said:
Thanks gentlemen, I was over thinking You have to calculate 120 x 1.73 to get 208. So I will get 83 amps per phase.
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That is incorrect. VL = 208, VP= 120. Like Augie said, you could look it at as (3) 10kVA 120V transformers --> 10kVA / 120V = 83A, or if you look at it as 3-phase, 30kVA divided by (208V * 1.73) that will give you the 83A.
 
Rock86 said:
That is incorrect. VL = 208, VP= 120. Like Augie said, you could look it at as (3) 10kVA 120V transformers --> 10kVA / 120V = 83A, or if you look at it as 3-phase, 30kVA divided by (208V * 1.73) that will give you the 83A.
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My math is wrong But Per phase is still 83 amps correct? so in a three phase panel My main will be 100 amp with capability of pulling 83 amps per phase which will give me a panel compacity of 249 if equally distributed between phases.
 
It doesn't work like that exactly. Plain and simply... if you have a 3-phase system with a 30kVA transformer supplying a 120/208 3-phase system, your capacity would be 83A.
 
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