?
Friday, February 26, 2021
Question:
Hello,
My question is what is the size overcurrent protection for a 75 kVA transformer, 3 phase, 4-wire, 480 primary, and 208Y/120 secondary?
Thomas Gentry
A
Answer:
Greetings Thomas,
Section 450.3 and Table 450.3(B) with Notes are used to determine the overcurrent protection size. This question presumes the OCPD is installed on the primary side of the transformer. Based on the Standard Ampere Rating Table in 240.6(A), 125 amperes would generally be required (112 amperes round up to the next higher size).