Why do you measure 415v between phases?

Answer 1

Answer for UK, Europe and countries running a 50 Hz supply service.

This measurement must be taken in a European country. The three phase system there uses 415 volts. On a three phase four wire wye system the voltage to neutral will be 415/1.73 = 240 volts. Voltages will be L1 - L2 = 415, L2 - L3 = 415, L3 - L1 = 415 volts, L1 - N = 240, L2 - N = 240 and L3 - N = 240 volts.

Another Answer

Your question should be asking, 'Why do you measure 415 V between lines?' The conductors that supply a three-phase load are called 'lines', not 'phases'. This is why voltages BETWEEN lines are called 'line voltages', whereas voltages ACROSS (i.e. not 'between') phases are called 'phase voltages'. It's very important to use the correct terminology or three-phase will get confusing!

The original answer explains this in terms of terminal markings, where 'L' represents a line conductor or terminal, and 'N' represents the neutral conductor or terminal, of a three-phase, four-wire, system.

But, to answer your question...

Before the requirements to harmonise nominal voltage levels throughout the EU (European Union), the standard three-phase nominal voltage values in the United Kingdom used to be 415 V (line voltages) and 240 V (phase voltages) respectively, with an allowable variation of +/-6%. Note that a line voltage is always 1.732 larger than a phase voltage.

To comply with EU harmonisation requirements, the UK has since changed its nominal voltages to 400 V (line voltages) and 230 V (phase voltage) respectively, with an allowable variation of +10%/-6%.

In practise, this has been a 'paper exercise' as no changes to the 'actual' voltages has ever taken place; it's only the 'nominal' (i.e. 'named' or 'stated' values) values that have changed -you will note that the allowable variation has changed to cater for this.

Answer 2

415 V used to be the standard nominal line voltage for three-phase systems in the UK. This value of line voltage resulted in a nominal corresponding phase voltage of 240 V required for residences, etc. Remember, a line voltage is 1.732 larger than the phase voltage.

However, since 1995, in order to 'harmonise' with other European Union countries, the UK's nominal line voltage has since been changed to 400 V, giving a nominal phase voltage of 230 V.

'Nominal' means 'named'; it is not necessarily the actualvoltage you would measure using a voltmeter. This is because government legislation allows supply voltages vary, within specified limits, either side of the stated nominal voltage.

Although the 'nominal' value has been changed from 240 V to 230 V, no 'actual' change has actually taken place. Instead, the UK's voltage standard has simply been changed from 240 V (+/- 6%) to 230 V (+10/-6%) -thus ensuring that the EU harmonisation requirement is met without the need for any actual changes to the electricity supply system!

Answer 3

alternating current keeps on fluctuating as is not steady.therefore one needs 415v which is rms voltage as 415v may rise above 415v .