Electrics and gas

Red and black cores, or brown and blue: what does cable colour actually tell a buyer?

Colour is a clue to age, not a test result and not a date certificate. Older cable often shows red and black, and later cable often shows brown and blue. The surveyor has not dated the installation from the plastic, and they have not tested either colour.

Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.

What is the fuller explanation?

You will see the cores at a fitting only if a cover is already off, or at a damaged end in a loft. A home survey does not remove electrical fittings to check the colours behind them. Mixed colours in one house are common, because kitchens, showers and loft lights are added at different times. The report can say which colour was visible and where. It should not pretend that brown and blue means the hidden runs were renewed, or that red and black means every circuit has failed.

There is no need to treat a colour change as a legal cutoff you can quote at the seller. The safety of the circuit is what an EICR looks at, and that inspection is not what you bought with the home survey. Landlords in the private and social rented sectors have a duty to have installations inspected at least every five years. An owner-occupier seller does not hand you that duty. If an electrician later uses C1, C2, C3 or FI, keep those codes off the RICS scale. Ask them what they tested, not what colour the sheath was.

What should you ask your surveyor?

Where did you see the core colours, and where were fittings still closed?
Are both colours present, or only one?
Are you treating colour as a clue, not as a test?

What are the typical next steps?

Do not unscrew sockets to compare colours.
If age of the wiring matters, ask for an EICR rather than a colour argument.
Tell the electrician about any mixed colours the survey actually saw.

Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.

Also asked about this

Does brown and blue prove the house was rewired?

No. It suggests some newer cable. Other circuits can remain older. Only tracing and testing can say.

Can you date the board from the cable colour alone?

No. Colour is not a certificate and not a calendar. The survey did not make it one.