When you have multiple phases (lines with voltages having
different phase angles)there different ways of defining
voltage. Say you have 4 lines: Line A, Line B and Line C
and Neutral. Now let's say you have a "3 phase" source of
480V connected to these lines. Each line represents
If you were to measure the voltage between, arbitrarily
choosing Line A and Line B, you would measure 480V. Now,
if you were to measure the voltage between Line A and
Neutral you would measure a much lower voltage. Namely,
480V divided by the square root of 3. This difference
shows that each 'line' is not actually carrying 480V. But
when you reference one non-neutral line with another non-
neutral line you get 480.
This is because you are referencing two voltage lines that
are out of phase with each other (in this case 120 degrees
out of phase). Therefore, the voltages will not be
in 'sync' and the differences will result in higher peak
voltages (480 in this case).
Line voltage is the potential difference between two lines of different phases. This means there are actually 3 line voltages on a three-phase system; A-B, A-C, and B-C. For a balanced system, the three must be equal.
Phase voltage is the potential difference between a line and neutral. A three-phase system has three phase voltages as well; A-N, B-N, and C-N. For a balanced system, all three must be equal.
For three-phase Alternating Current (AC) circuits, there is a relationship between line and phase voltage that is defined by the connection method (wye or delta).
For single-phase circuits (AC and DC), line parameters (current and voltage) are the same as phase parameters. This is because one leg is referred to as having 'potential', while the other is generally referred to as the 'return' or 'neutral' or 'ground'.