NEC Article 450 - Transformers

[wbd]

hello,
this is probably a real basic question but in NEC Article 450, Table 450.3(A) and (B), when transformers are refered to as Over 600 volts or 600 volts and less, is this the primary voltage? I'm assuming it would be the highest voltage. For instance, a 13.8 kv /480V transformer would be on Table 450.3(A) and a 480V/120V transformer would be on Table 450.3 (B).
Also, where would the definition of the 600 Volts is primary or highest voltage be found in NEC? I've looked in several places but obviously not the right spots.

Thank you in advance.

 

[dpc]

It's the highest voltage. Table 450.3 (A) has separate columns for primary and secondary sides and separate requirements for secondary winding over or under 600V. If any winding is over 600V, it falls into this category. Table 450.3(B) for 600V and below has no provision for any winding being over 600V, unlike Table A. I don't think this is specifically defined anywhere, but that's the intent. If you look at the tables, I don't think any other interpretation would be reasonable.

One fallacy in Article 450 is the presumption that the primary is always the highest voltage. Technically, this is not always the case. For generator step-up transformer, the primary is the lower voltage. But this doesn't really change the intent of Article 450.