Transformer Feeder sizing
- Thread starter Jim Horn
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- Lockport, IL
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- Semi-Retired Electrical Engineer
Quick and simple way: Multiply the 600 times 208 and divide by 480 (i.e., the ratio of secondary to primary voltage). I get an answer of 260 amps.
Better (and more consistent) way: Start with the transformer rating in KVA. Divide by the primary voltage (or the secondary voltage, if you are working on that side), and divide again by 1.732 (the square root of three). I get an answer of 270 amps (primary) and 625 amps (secondary). Those are the actual transformer current ratings. If you put on a load that is smaller than the secondary rating (i.e., 600 versus 625), then the primary current will also be smaller (i.e., 260 versus 270).
Welcome to the forum.
Better (and more consistent) way: Start with the transformer rating in KVA. Divide by the primary voltage (or the secondary voltage, if you are working on that side), and divide again by 1.732 (the square root of three). I get an answer of 270 amps (primary) and 625 amps (secondary). Those are the actual transformer current ratings. If you put on a load that is smaller than the secondary rating (i.e., 600 versus 625), then the primary current will also be smaller (i.e., 260 versus 270).
Welcome to the forum.
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