ELECTRICAL VOLTS QUESTION
I got this practice exam question the other day but dont understand it...
If the voltage between the neutral and the peak of a threephase current is 120 volts, what is the voltage between two phases?
a 120
b 208
c 240
d 277
the answer is below. but first off what is a "neutral" and what is "the peak"? Where did this equation come from?
V2 = V1 / square root of 3
V1 = V2 x square root of 3 = 120vx1.73 = 208v
Any help would be greatly appreciated. Also, some images are attached from the book. how do you know for instance the 3 phase transformer schematics image that between the lines it 240v or 120v between two other lines?
Hope this makes sense..

Hi Baylee,
Do you have the PPI2pass study material for Project, Planning, and Design? If so, it explains this pretty well on page 1723. The diagrams are a little more simplified. Essentially, the lower number of any of the four service types (120/240, 120/208, 277/480, and 2400/4160) goes between the neutral wire and a hot wire. The higher number goes between two hot wires. It helped me to memorize the four different service types and which phases and number of wires is associated with each. Shouldn't be any calculations necessaryjust pure, oldfashioned memorization. =)
I hope this helps!

Great answer above.
This is a helpful video to understand "phases" . The advantage being higher power without the need for thicker wires, and more smooth delivery of power to machinery
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