3Phase + Neutral, 208VAC distribution and conversion to 1Phase 120VAC

Question

Question 1: How to convert 3phase+Neutral 208VAC supply to 1phase 120VAC? Can I tap off one (any) leg of the 3phase supply and use that to Neutral to get the 120VAC? Or do I have to use all three phases and load each phase similarly to balance the load of the 120VAC equipment across the three phases?

Question 2: We want to step the voltage up from 3phase 208VAC to 3phase 800VAC and the Step up transformer is wired delta, so we just send the 3 phases to the final load right? Or do we have to continue the neutral line to the final load somehow too?

Answer 1

If you are having to ask then be clear that you are not qualified to carry out the work. If you are seeking understanding so that you can request a quotation for someone qualified to do the work then:

1. \$ V_{L-N} = \frac {V_{L-L}}{\sqrt 3} = \frac {208}{1.73} = 120 \ \mathrm V\$ so, yes, that will work. Generally the supply should be able to take an imbalance but there are too many unknowns in your question to answer definitely.

2. If the secondary is wired in delta than you have no neutral and the transformer is floating with respect to neutral. You cannot connect neutral to your load neutral.

Again, at 800 V AC this job is not for amateurs.