JasonC
Member
- Location
- N. Andover MA
My question regards to the 120% rule as it applies to transformers. The site I have has 3ph 4w 208/120 service 1600A cabinet 1000A main. It has a spare 400A and 250A breakers. I am planning on using 4 20kw Tl inverters (480V), that is where I need some assistance. The 400A equals 143kVA, I assume I need to derate (Constant Current) that 400A since it will be in a PV Array. That would mean the 400A would really equal (333.3A) 119kVA. Now that 119kVA on the secondary side (480) would equal 144A (not including transformer losses). Since I have covered the OCPD on the primary side and it is derated for constant current, I now look at the secondary side. If i take the 144A and figure for the OCPD on either side 150A (125kVA) and 125A(103.8 kVA), I still have to derate those OCPD's for continuous use. If I use the 150A, I can only input 125A into that OCPD which equals 103.8 kVA. I have lost roughly 15 kVA in code losses. If the 150A was the corrected amperage the uncorrected amperage would be 180A. I guess my real question is would a 125 kVa transformer be the correct fit and is the 150A on the 480 side correct.