What is this?
The UK changed its wiring colour codes in 2006. Old wiring uses red (live), black (neutral), and green/yellow (earth). New wiring uses brown (live), blue (neutral), and green/yellow (earth). Many UK homes have a mix of both colour codes where new circuits have been added alongside existing wiring. This is perfectly legal and common, but it can cause confusion and mistakes if not properly identified.
Common causes
- New circuits added to a property that still has pre-2006 wiring
- Partial rewire has replaced some cables but not all
- Extension built with new wiring connected to existing old-colour circuits
- Consumer unit replaced but cables not changed
- DIY work mixing old and new cables without proper identification
Is it dangerous?
The mixed colours themselves are not dangerous — both systems are safe when correctly installed. However, confusion between old and new colour codes can lead to serious mistakes. In the old system, black is neutral; in the new system, blue is neutral. If someone confuses these, they could connect a live wire where neutral should be. This has caused fatal accidents. All mixed-colour installations should have clear warning labels.
Can I fix it myself?
No. You should not attempt to work on wiring with mixed colour codes unless you fully understand both systems. If you are changing a light fitting or socket and find mixed colours, stop and call an electrician. Never guess which wire is which based on colour alone without understanding the context.
When to call an electrician
Call an electrician if you find mixed colours and are unsure about any connections, if there are no warning labels on the consumer unit, or if you want to do any work that involves connecting to existing wiring. An electrician will correctly identify all conductors and add appropriate labels.
What will an electrician do?
Identify and label all conductors correctly at the consumer unit and junction boxes
Apply BS 7671 warning notices where old and new colours coexist
Check all connections to ensure the correct cores are connected appropriately
Recommend upgrading old cables if they are deteriorated, regardless of colour
Typical cost
£80 – £200
Labelling and checking connections is at the lower end. If wiring needs replacing due to age rather than just colour, costs increase significantly.
