Electrical Engineering
Electronics Engineering
Electrical Wiring

Why is 1 phase 240 volts and 3 phase 415 volts?


User Avatar
Wiki User

In a three-phase, star- (or wye-) connected, system the line voltage (line-to-line voltage) is 1.732 (or the square-root of 3) times the phase voltage (line-to-neutral voltage). The reason for this is that a line voltage is the vectorial sum (not algebraic sum) of two phase voltages displaced from each other at 60 degrees.

These days, incidentally, the UK's nominal phase voltage is 230 V, and its corresponding line voltage is 400 V.