transforemr connection for 240/416 vs 277/480

huntinchief

Member
I know if I connect three 120/240V transformers in a wye bank I will get 120/208V. Therefore, I assume three 240/480V transformers wye connected would provide 240/416V. If this is true how is 277/480 derived? What am I missing?

kwired

Electron manager
I know if I connect three 120/240V transformers in a wye bank I will get 120/208V. Therefore, I assume three 240/480V transformers wye connected would provide 240/416V. If this is true how is 277/480 derived? What am I missing?
A wye bank built with 120 volt transformers will have output of 120/208.

If built with 240 volt transformers the output will be 240/416.

The multiplier is 1.73 times the voltage to the neutral is the line to line voltage.

A 277/480 bank is made of three 277 volt transformers.

If you used three 480 volt transformers you would have a 480/831 volt system.

The center taps of each individual transformer in the bank are left unused and can be assumed to not exist for the most part, they are not there for use in this particular configuration. That said, most popular transformers used for building 120/208 or 277/480 systems do not have a center tap as there is not much need for the resulting voltage if those transformers were to be used for single phase systems.

Hv&Lv

Senior Member
When three 120/240 single phase XF's are banked together for a 208Y/120, there is a little more work than simply connecting wires for this to happen. The top has to be removed and the coils have to be connected in parallel (A-C, B-D on the terminals), rather than in the normal series configuration they are shipped with. Here you get, as kwired stated, three 120 volt transformers banked together to produce 208Y/120. Look up at a 208 bank, you will see one secondary terminal with nothing connected to it. it is useless since there is nothing connected to it on the inside once we get done with the conversion.

We can and do get 277/480 the same way. They come in handy when powering up a bunch of lights at 277 single phase.

erickench

Senior Member
I know if I connect three 120/240V transformers in a wye bank I will get 120/208V. Therefore, I assume three 240/480V transformers wye connected would provide 240/416V. If this is true how is 277/480 derived? What am I missing?
The only you could derive a 480 Volt system using what you mentioned in your post is to connect three 480 Volt transformers in a delta. If you wanted to create a neutral you could use a zig-zag transformer.

Electric-Light

Senior Member
I know if I connect three 120/240V transformers in a wye bank I will get 120/208V. Therefore, I assume three 240/480V transformers wye connected would provide 240/416V. If this is true how is 277/480 derived? What am I missing?
The same way.
transformer voltage x sqrt(3) = phase to phase.