scheme are clearly labelled. From April 2006, only the new colours should be used for any new wiring. Potential for confusion The UK changed colour codes three decades after most other European countries, as in 1977 the change of neutral and phase colours was not considered safe by the IEE. Blue, previously used as a phase colour, is now the colour for neutral. Black, which was previously used for neutral, now indicates a phase. Household wiring does not usually use three-phase supplies and the clash only occurs in three-phase systems. Wiring to the old standard can be detected by use of a red wire. The new standard colour code does not use red. Where new wiring is mixed with old, cables must be clearly marked to prevent interchange of phase and neutral. Variation in the earth/ground conductor's colour at an earlier date that the remainder of the colours means its colour should not be used as an indication of the old vs new standard cable or colour assignment. Other colour schemes On telecommunications nominal 48 V DC supplies, the live is usually −42 V (flat batteries) to almost −57 V (float charge). The IEC currently specifies a colour-coding for new local DC distribution. These are: There is a long history of colour changes; prior to 1964 white was used instead of yellow as the second phase, and before World War II, a black earth and a green third phase in place of green earth and white phase was permitted. The regulations permitted (and still do) the use of any wire colour that is not an earth colour, providing it is unambiguously identified at all connections by clear labelling or by correctly coloured over-sleeving. It was not uncommon on commercial builds of the 1960s with a three phase supply for the phase colours (red, yellow, blue) to be used throughout single phase sub circuits thus indicating the phase origin of the supply, in this case no over-sleeving was used and can give rise to confusion when encountered today. Direct current mains supplies are only of historical interest in the UK but the colour coding was red for live and black for earthed (regardless of the polarity). Hardly any loads were polarity sensitive when direct current systems were introduced (principally incandescent lighting, heating systems or series direct current motors) and it was considered more important to identify the live wire than the