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?

  • \$\begingroup\$ Does application always provide balanced load? using Y-delta step up is not advised due to imbalance on power interruptions with voltage imbalance. \$\endgroup\$ Mar 4, 2018 at 16:49
  • \$\begingroup\$ @TonyStewart.EEsince'75 No, the load will most likely not be balanced. Can you elaborate on the Y-Delta step up and why it is not advised? I think the people who are working on this currently have issues with unbalanced loads. I am just interested in this topic and would to know more about this if possible please. \$\endgroup\$
    – Douglas
    Mar 4, 2018 at 19:39

1 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.


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