Re: three phase transformer
Three phase transformers behave more ?nicely,? if you keep the load balanced among the three phases. But yes, you can put a large, single-phase load on the secondary of a three-phase transformer.
However, the way they build a three-phase, 10,000 VA transformer is to take three individual, single-phase transformers, each rated at 3,333 VA, and connect them in whatever configuration (i.e., Wye or Delta) is needed. So if you want to power a single phase, 4,000 VA load, that would exceed the rating of your transformer. So, no, you can?t do what you propose.