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  1. TheDawg

    Code Reference For Transformer Secondary Protection Requirement

    Can someone please provide a code reference for when it is required to have secondary protection on a transformer (less than 600VAC and greater than 9 Amps)? I am interested in utilizing FPN #2 & #3 of NEC Table 450.3 (B), but am unclear on the intent of the phrase in FPN #2 that states: "Where...
  2. TheDawg

    Power Transformer Question

    Thank you for the comments dpc. I am also thinking that the intent of the code would pertain to a situation where the secondary of a transformer is tapped to feed 2 ea. Main Lug 225 Amp Rated Load Centers, then the wire would need to be sized per the full "rating" of the device (ie. 225 Amps)...
  3. TheDawg

    Power Transformer Question

    I agree with your comments, and this is how I would approach conductor sizing for these applications. But I did not design it and I was hoping to site the NEC for a clear definition on this. The calculated load is less than 180 Amps, the MCCB is correctly sized at 225 Amps, the unprotected...
  4. TheDawg

    Power Transformer Question

    Thank you for the NEC reference. Based upon condition of acceptability 240.21 (C)(2)(1), I am still confused by the requirement for the secdondary conductor ampacity to be not less than the combined calculated loads AND not less than the rating of the device supplied by the secondary conductors...
  5. TheDawg

    Power Transformer Question

    I am working on a Power Distribution Unit where the ETL Listed Equipment has a 500A Main CB feeding a 300kVA Delta-Wye Transformer (480: 208/120). The Transformer Secondary Feeds Six 225 Amp Molded Case Circuit Breakers (ie. Primary Protection Only). What NEC Sections would pertain to the...

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