Is Transformer Secondary protection needed?, correct me if I'm wrong...

[electricus]

I have a 480V single phase 7.5kVA transformer, primary side is protected with a 15A breaker (that is what I have available).

According to Table 450.3(B) under the "primary only" "currents of 9 amps or more "125%" can I use the "not required" for the secondary protection. In other words I'm protected on the primary side at 125% (or less), I read it that I don't need secondary protection.

The panels are side by side, was trying to save on needed a main breaker in the small (6 space?) 120/240v panel.

Also as a side note when figuring current draw for this example. Just the very basics, if I have 480V, 15A single phase on the primary at 100% duty, then I will have 240V 30A single phase on the secondary. What is the current available for a 120V load, still 30A right?

 

[buddhakii]

If you have no more than 6 handles you don't need a main

 

[augie47]

Normally they key here is the secondary voltage configuration. Per 240.4(F) transformer secondary conductors are protected by the primary in two-wire/two wire or delta/delta arrangements.
If your secondary is 240/120 you will need secondary protection, from that rule you would need secondary protection, however, since your secondary feeds a panel, 408.36 requires a main.

 

[jim dungar]

Article 450 concerns the transformer only.
You also need to consider article 240, in regards to protecting the secondary conductors, most people end up in 240.21(C).
Finally you need to look at 408 for the panel itself.

With proper layout and sizing, a single device may meet several of the above requirements.