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have a 30 kva transformer feeding a 100 amp 208/120 need to add 70 more amp to load.the phases are reading A-9.2 B-1.7 C-1.6 the 30 amp breaker feeding the transformer is from a 480/277 panel.that main breaker is a 50 amp being feed from the outside 100 amp fuse disconnect. will i have to chage any breaker size.from the main fuses to the 480/277 panel and to the 208/120 panel.

What type and size conductors on the secondary???

Do you have a 30 and a 50amp pri OCP??

Look at 450.3(B) and the table
240.6.

kVA = V.A / 1000 Single phase
kVA = V.A.1.73 / 1000 Three Phase

or read the charts

Charlie