Grey used as a Neutral

by Steve on May 4, 2009



Should I identify black or grey as neutral on harmonised single phase cables?


Technically, when any cable is over-sleeved or marked (with the exception of single-core green/yellow which must not be over-sleeved or marked), the over-sleeve or marking takes precedence over any colour underneath and therefore any combination can be used.

However, a convention has been generally accepted of over sleeving or marking the black with green/yellow (CPC) and the grey with blue (Neutral).

The thinking behind this has been done with the aim of helping disassociate the colour black with neutral and the grey becoming a neutral colour where no blue core is present.


Where a cable has no blue core it’s a good rule to identify/use the grey as neutral with blue sleeving.

Where a cable does already have a blue core it can be a good rule to identify/use the grey as earth with green and yellow sleeving.

Please be very careful when working on 3 phase installations with the old colour markings which used black as the neutral and blue as a phase (L3). It can be very easy to confuse them when re-terminating older cables which can obviously lead to serious problems.

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