You will use over 1000V for primary and 1000V or less for secondary.
In your example (assuming any location and Z<6%)
Primary:
Fuse would be rated at 300% of FLA or next higher standard size
Circuit Breaker would be rated at 600% of FLA or next higher standard size
Secondary:
Fuse would be rated at 125% of FLA or next higher standard size
Circuit Breaker would be rated at 125% of FLA or next higher standard size
Hey, I'm circling back to this because I'm still a bit lost.
So let's say for example: a 3-ph, 13000 V / 240 V transformer.
If you were asked for BOTH primary and secondary protection for such a transformer, you have to use both tables even for just this one transformer? So the Table for Over 1000 Volts used on the primary side, and the Table for 1000 Volts and less on the secondary side?
I'm just asking and trying to confirm, because I've never dealt with a question like this before. Most of the transformer OCPD questions I've done only asked for primary only protection...
Another reason I'm a bit confused about this is because of how the tables are labeled:
Table 450.3(A): Maximum Rating or Setting of Overcurrent Protection for Transformers Over 1000 Volts
Table 450.3(B): Maximum Rating or Setting of Overcurrent Protection for Transformers 1000 Volts and Less
To me, based on the table titles, it sounds like you are actually supposed to use Table 450.3(A) for a transformer over 1000 volts, for both windings, even if only one winding is actually over 1000 V and the other isn't. And if the transformer in question does not have a winding over 1000 V, then you use Table 450.3(B).
Unfortunately for me I've never seen such a practice question like this, so I don't know...