120/215/120 Do I need a transformer to get standard 208V??? No One Can Answer

[Little Bill]

You can both see my confusion here; I have several senior members saying I do & do not need a buck boost.... a 12% buck boost at 40A is listed at $2800!!!

I think the ones saying you don't need a BB transformer are just saying it is common to connect a 208V motor to 240V. Also, it won't hurt much to connect the heating elements rated for 208V to 240V. It will heat faster but could burn the elements out sooner as has been said.

Although practically speaking, you can connect between the grounded/neutral and the high leg to get somewhere around 208V, it is impracticable for a few reasons:
The voltage probably won't be stable and is not meant to be used that way
You won't find a breaker (without going to a 2 or 3P breaker) that is rated for straight 240V or 208V, they will be slash (/) rated 240/120 or 208/120.
You have to use a breaker that can handle the highest voltage from line to neutral. With your needed voltage, 208V, a (/) slash rated breaker would either be 240/120 or 208/120, the 120 would not be compliant since it is less than the provided 208V high leg to neutral.
So a BB is going to be your best route in this situation.

 

[petersonra]

I think the ones saying you don't need a BB transformer are just saying it is common to connect a 208V motor to 240V. Also, it won't hurt much to connect the heating elements rated for 208V to 240V. It will heat faster but could burn the elements out sooner as has been said.

Although practically speaking, you can connect between the grounded/neutral and the high leg to get somewhere around 208V, it is impracticable for a few reasons:
The voltage probably won't be stable and is not meant to be used that way
You won't find a breaker (without going to a 2 or 3P breaker) that is rated for straight 240V or 208V, they will be slash (/) rated 240/120 or 208/120.
You have to use a breaker that can handle the highest voltage from line to neutral. With your needed voltage, 208V, a (/) slash rated breaker would either be 240/120 or 208/120, the 120 would not be compliant since it is less than the provided 208V high leg to neutral.
So a BB is going to be your best route in this situation.

Why would it be "unstable"? Granted the only practical CB option is probably a 3 pole unit but if there is space for it who cares?

 

[Little Bill]

Why would it be "unstable"? Granted the only practical CB option is probably a 3 pole unit but if there is space for it who cares?

If you've ever measured voltage on a Delta high leg you would see that it varies widely anywhere from 206V to 218V depending on the transformer(s) and load. The 208V (line to neutral) is just a byproduct of the Delta configuration and is not meant as a usable voltage.

 

[kwired]

If you've ever measured voltage on a Delta high leg you would see that it varies widely anywhere from 206V to 218V depending on the transformer(s) and load. The 208V (line to neutral) is just a byproduct of the Delta configuration and is not meant as a usable voltage.

That can depend on whether they have three same sized transformers, or a larger 120/240 pot and smaller pot for high leg, or even sometimes full delta with larger 120/240 pot but other two are smaller.

If you have a system that was designed for minimal load on the third phase, but start to load it more then was intended, then impedance of that winding is going to draw voltage down on that leg, whether the load is three phase, single phase line to line, or single phase line to neutral.

If you have a system designed for "power" and have three same sized transformers I'd bet you see similar draw down in voltage as the other lines when reasonably balanced loading anyway.