Dave the way i see it, on 4-wire secondary transformers, the primary OCPD doesn't protect the secondary conductors "at their ampacity" because of the secondary to primary ratio. The primary OCP will be to high for the secondary conductors via this ratio. This would now fit the definition of tap conductors.
Rick
I think this is where you are going wrong. 240.4(F) say that transformer secondary conductors (other than 3 wire delta) shall
NOT be considered to be protected by the primary OCPD. If you had a 45kVA, 480-240V delta (3-wire) transformer with a 60A primary OCPD and #1awg secondary conductors, the secondaries can be protected by the primary OCPD because of the ratio you mention. However, if you had a 45kVA, 480-240/120V delta (4-wire w/a center tap) the secondary to primary ratio is still the same, but the secondaries cannot be protected by the primary OCPD. Or if you had a 45kVA, 480-208/120V (wye) transformer with a 60A primary OCPD and #1/0awg secondary conductors, the primary OCPD again does NOT exceed the value of the secondary conductor ampacity times the secondary to primary ratio. But again, the primary OCPD cannot be used to protect the secondary conductors even though the primary OCPD is not to high. The secondary to primary ratio has nothing to do with whether the secondary conductors are taps.
240.21 says that overcurrent protection shall be provided for each (ungrounded) conductor at the point they receive their supply, except as permitted in 240.21(A) thru (H). 240.21(A) tell us how to deal with
branch circuit TAPS, 240.21(B) tell us how to deal with
feeder TAPS, and 240.21(C) tells us how to deal with
transformer secondary conductors. Transformer secondary conductors are
neither branch circuit taps
nor feeder taps.
Going back to the definition of Tap Conductors in 240.2, there are two conditions that must be met for conductors to be tap conductors: they must have an OCPD ahead of its point of supply, and the OCPD must exceed the value permitted for similar conductors protected as described elsewhere in 240.4. The point of supply for the transformer secondary conductors is the transformer secondary. There is no OCPD ahead of their point of supply, so by definition, the transformer secondary conductors are not tap conductors.