I'm proposing to install a new 15 KVA 480v prim. 120/208 sec. to feed a 3-phase 50-amp panel for a new modular office in a warehouse. I am going to use the 3-pole 480v breaker as disconnecting means as required (NEC 2002 110.58). The panel is in sight about 100' away, as long as no new shelves, machines, etc. aren’t put in the way in the future to obstruct the view.
I thought there was an exception to allow the disconnect not to be within sight as long as there was a means of locking it out. I can’t seem to find one that applies to transformers.
Also, if I protect the primary at 125%, do I not need to supply secondary protection?
Do I understand Table 450.3(B) correctly in that 125% primary protection means no sec. protection, and 250% primary protection means 125% sec. protection?
So, minimum design says 480-volt 25-amp breaker within sight about 100’ away to 15KVA xfmr to MLO panel with branch breakers. What does good design say and why?
Also, grounding only at transformer to building steel right? No bond screw at the panel.
Thanks
