sparkyguy545
Member
Application:
3-Phase 1500 kVA Dry-Type Xfmr w/5.75%Z (therefore <6%).
Primary 4.16 kV Delta (208 FLA)
Secondary 480Y/277; 4-Wire solidly grounded (1804 FLA)
Applciation definitely qualifies as "Supervised Location". In fact, it is for the Water Division of a combined Electric/Water Utility. Note that we are to design for NEC, not NESC.
Questions:
1. Can I install transformer Primary Protection Only (at 300% or next highest) and hard-bus to a MLO Swbd?. Initially, I thought 450.3(A) implies this was allowed. However, I believe 240.4(F) mandates I include secondary OC protection since I have a 3-Phase, 4-Wire secondary. Comments appreciated.
2. The xfmr primary conductor ampacity (medium-voltage or not) must be equal-to, or greater than, the upstream OC protection, right? In my case, if I size Primary protection @ 300%, the upstream OC prot (a vacuum-breaker in my case) will be about 600A requiring Parallel 250 kcmil MV-90 Cu cable between breaker and xfmr primary. That's a lot of copper for a xfmr FLA=208 Amps! I recognize the 300% is a maximum, and I'm allowed to go lower, but it seems WAY oversized.
3-Phase 1500 kVA Dry-Type Xfmr w/5.75%Z (therefore <6%).
Primary 4.16 kV Delta (208 FLA)
Secondary 480Y/277; 4-Wire solidly grounded (1804 FLA)
Applciation definitely qualifies as "Supervised Location". In fact, it is for the Water Division of a combined Electric/Water Utility. Note that we are to design for NEC, not NESC.
Questions:
1. Can I install transformer Primary Protection Only (at 300% or next highest) and hard-bus to a MLO Swbd?. Initially, I thought 450.3(A) implies this was allowed. However, I believe 240.4(F) mandates I include secondary OC protection since I have a 3-Phase, 4-Wire secondary. Comments appreciated.
2. The xfmr primary conductor ampacity (medium-voltage or not) must be equal-to, or greater than, the upstream OC protection, right? In my case, if I size Primary protection @ 300%, the upstream OC prot (a vacuum-breaker in my case) will be about 600A requiring Parallel 250 kcmil MV-90 Cu cable between breaker and xfmr primary. That's a lot of copper for a xfmr FLA=208 Amps! I recognize the 300% is a maximum, and I'm allowed to go lower, but it seems WAY oversized.