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Hi everyone,

The other day I was making a few measurements on a step-up autotransformer. The transformer is rated 208v/230v on the primary side and 460v/480v on the secondary side. I was always taught that for step-up transformers the primary side is L.V and the secondary side is H.V. However, yesterday I noticed the three-phase 208v source was connected to H1-H2-H3 on the primary side labeled as "H.V", meanwhile, the 460v output was connected to X1-X2-X3 on the secondary side labeled as "L.V". Why is it like this? All replies are greatly appreciated.

24V
 

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Some time ago, the NEC began requiring that transformers used for step-UP purposes be marked or otherwise indicated to be suitable for that purpose. After that, some inspectors interpreted that to mean that if a transformer was marked as "primary" and "secondary", it was only to be used that way. So transformer mfrs started changing to just label them as "HV" and "LV".
 
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