What is phase wire?

Answer 1

A phase wire is the hot wire in a circuit if looking at single phase that would be the live (brown in the UK). If you are trying to find out which wire is your phase wire use a voltmeter connect the black lead to earth and red lead on the wire to be tested. If the circuit is on and you have a phase wire you will read voltage on the meter. If the circuit is off or you have the neutral(blue wire in the UK) you will read little or no volts.

Notice electricity is dangerous always use common sense if you don't know what you are doing find someone who does failing that put a hand in your pocket you will have less chance of killing yourself.

Answer

'Phase' is the incorrect name widely used in place of the correct term, 'line'. The current version of BS 7671(2008), the IEE Wiring Regulations, has, at last, recognised the misuse of the term 'phase' in its previous editions.

In the UK, a single-phase AC line conductor has a nominal potential of 230 V with respect to the neutral. In Europe, a single-phase line conductor is normally colour-coded brown; in three-phase systems, the three line conductors are colour codes brown, black, and grey.