# Buck Boost Transformer Neutral



## Tandy (Sep 15, 2018)

Okay, so this is a part theory question/ practical application.

Currently on a job with a 3 Phase 120/208V system. Connected some equipment that was rated 120/240V single phase. The manufacturer rep came out to commission and put up a bit of fit, claiming the equipment could would burn out running at less than rated voltage. Im not necessarily disagreeing but thats not the point of this topic. In short they want us to install a 208V to 240V single phase buck boost transformer connected line A to B. A transformer with a center tap is not readily available, and because its a bit of a time crunch the engineer wants us to run the neutral through from the original panel.


First question is, is this even a code compliant installation? At first I would think not, however because the BB is an autotransformer there is still a electrical connection so its technically not a new system? 

The second is a theory related question. Did a little research on this particular scenario and because of the nature of the phase angles, once you boost the output voltage through the BB the phase to neutral voltages will not be equal. You would still get 120 to neutral on the common connection of the transformer, but the output leg would be somewhere around 148V to neutral. Can anyone verify this? 

I did try to figure this out with a few phasor diagrams and did calculate 148V, however i also ended up with a 6˚ phase shift that i cannot explain at all. There is a good chance this was just a calculation error, but i would love to be able to figure out the math behind this. So, thoughts or ideas anyone?


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## Tandy (Sep 15, 2018)

Not really sure why this was posted in the apprentice section?


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## Bird dog (Oct 27, 2015)

Tandy said:


> Not really sure why this was posted in the apprentice section?


Because that's where you posted it unless a Moderator moved it.


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## Tandy (Sep 15, 2018)

Bird dog said:


> Because that's where you posted it unless a Moderator moved it.


Pretty sure i posted it in the general section electrical discussion section, so I guess a mod moved it then. Im just curious as to why..?


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## Southeast Power (Jan 18, 2009)

We had recent thread about using a neutral around a BB TX.
I would go as far as to say that if the engineer was willing to specify a transformer, and provide a wiring diagram, I would do it.


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