Unfortunately for the UK, this harmonisation will probably necessitate a significant change and our red, yellow and blue phase colours will disappear (see figure 1).
However, the justification for keeping these colours is difficult. Most CENELEC countries use a combination of brown and blacks for phase colours. Switzerland is the only other country presently using red cables. Yellow cables are not used anywhere but in the UK and, indeed, are prohibited in some countries.
Even more significant to the debate is the fact that all other CENELEC countries use blue for their neutral, including the Republic of Ireland who changed to a blue neutral (from black) in 1990.
Given that CENELEC countries, including the UK, have agreed on blue for the neutral conductor, the UK has had to consider its position when faced with the rather bland 'palate' of brown and black for phase colours preferred by our mainland European colleagues.
How could an acceptable CENELEC compromise be reached? The initial proposal was for three browns, individually marked, but this was rejected by cable makers due to impracticability and possible reduction in cable manufacture production speeds.
Following this, CENELEC was keen to base harmonisation upon a brown and two blacks; obviously this would not have been good for the UK.
To improve upon the position, the UK has recently proposed brown, black and grey for the phase colours:
It appears that these proposed colours may very well be accepted by CENELEC countries, so what are the implications for UK contractors? Obviously these cable colours would constitute major change for installers and will necessitate a retraining process. Complications will arise when making connections to existing cables as in figure 1.
Further complications will arise in existing installations where single phase circuits have been wired in blue phase and black neutral.
This is not rare and was specified by consultants when the 15th Edition IEE Wiring Regulations was published in the 1980s; the practice can still be used under BS 7671: 1992.
Any new circuits wired in the proposed black (live) and blue (neutral) could totally confuse installers and maintenance staff. Confusion could also occur with the use of grey and blue single core cables.
The only practical answer for the UK electrical installation industry would be to prohibit the use of the new phase colours black and grey with blue neutrals except in multi-core cables. This would apply to three phase, four wire, single core installations (see figure 2).
It is only sensible that the UK must push for colours which are acceptable, to prevent enforcement of those which are not.
I am sure that most of us would love to hang on to our existing phase colours, indeed some feel there is nothing gained by changing installation practices. However, it is a legal requirement for the UK to change to a blue neutral conductor.
With these thoughts in mind the UK and the ECA are striving to achieve the most practical compromise, and so avoid the enforcement of less favourable Eurppean colour options.
Source
Electrical and Mechanical Contractor
Postscript
Darrell Locke is a technical manager with the ECA.
