Rewiring a house: when is it needed and how is it done?

Written by Engin Demirel · Electrical technician, master instructor · 12 years of experience

Short answer: An installation needs attention if it is more than 25–30 years old, the sockets are not earthed, there is no residual current device (RCD) in the consumer unit, breakers trip often, sockets and plugs get hot or discoloured, or new large loads such as air conditioning, a built-in oven or an EV charger are being added. Rewiring starts with measurement: earth, insulation and RCD tests show which circuits can stay and which must be replaced. In most homes the biggest safety gain comes from a new consumer unit (30 mA RCD protection, correct breakers) and proper earthing.

Signs of an old installation

Most sockets are unearthed.
There is no RCD in the consumer unit, or it does not trip when the test button is pressed.
Old rewirable fuses, or breakers that trip often.
Sockets, plugs or switches get hot, are discoloured or crackle.
Lights flicker or dim when a large appliance starts.
Cable insulation that has hardened or cracked where it leaves the wall; aluminium conductors.
Too many sockets on one circuit and heavy use of extension blocks.

If you notice even one of these, have an electrician check it; hot and discoloured connections are a fire risk.

Measure first: which circuits stay, which go?

Earth measurement: is there an earth, and is its resistance low enough?
Insulation test: is the cable insulation sound? Low values point to damp or worn cable.
RCD test: does it trip at the right current and within the right time?
Circuit and load check: which breaker feeds which circuit, and are cable sizes right for the load?

Depending on the results, some circuits can be kept and only the consumer unit and outlets renewed; in other homes all cables must be replaced.

Partial or full rewiring?

Partial: a new consumer unit, an earth conductor, new sockets and switches in some rooms, dedicated circuits for large appliances. The most economical route if the cables are sound and can be replaced through existing conduit.
Full: all circuits are run again. Sensible if cables are buried in plaster without conduit or the insulation is poor, and especially when a renovation (plaster, paint, kitchen and bathroom) is planned anyway, since walls will be opened in any case.

What a rewire includes

Consumer unit: circuits split onto separate breakers, 30 mA RCD protection added (type A preferred) and, where needed, surge protection. Most national wiring rules require 30 mA RCD protection for socket circuits in homes.
Earthing: a separate protective conductor (green-yellow) connected to the building earth reaches every socket and metal-bodied fixture.
Circuits: typically 1.5 mm² for lighting and 2.5 mm² for sockets (local rules decide), with dedicated circuits for ovens, air conditioning, water heaters and EV chargers.
Colour code: live brown (three-phase brown, black, grey), neutral blue, earth green-yellow. Mixing old and new colour codes causes mistakes during maintenance.
Outlets: earthed sockets and new switches; suitable IP ratings in wet rooms.

Supply capacity and three-phase

If new large loads (electric hob, heat pump, EV charger) are being added, the connected capacity with the distribution company may also be too small. An increase or a change from single-phase to three-phase may be needed. Knowing this before rewiring changes the choice of consumer unit and cables.

Rewiring an occupied home

A full rewire can be done room by room in an occupied home, planned so that power can be restored at the end of each day. If walls are chased there will be dust and noise and furniture needs protecting. Surface trunking reduces chasing but changes the look; concealed wiring is cleaner.

What drives the cost?

Size of the home and number of points (sockets, switches, lights)
Whether cables can be pulled through conduit or walls must be chased
Number and brand of protective devices in the consumer unit
Whether the earthing must be redone
Switch and socket range and light fittings
Whether plastering and painting are included

A price should be itemised after the survey and measurements.

In Bursa with ENGN

In Bursa, Turkey, we carry out electrical installations in villas, apartments and offices from the foundations to handover, and assess larger renovation work according to its scope during the site survey. See our electrical contractor page for details and quotes.

Frequently asked questions

How often should a house be rewired?

There is no fixed interval; insulation and connections deteriorate with age. Installations older than 25–30 years, without earthing or without RCD protection, should be tested and renewed where needed.

Can a house be rewired without chasing walls?

If the cables run in conduit, old cable can often be pulled out and new cable drawn through the same conduit. Cables buried without conduit need chasing or surface trunking.

Is an RCD required in an older home?

Most wiring regulations require 30 mA RCD protection for socket circuits in homes. Adding one to an older consumer unit is the most important safety upgrade.

What if the sockets are not earthed?

An earth conductor has to be installed and the building earth measured. Plugging earthed appliances into unearthed sockets increases the risk of electric shock.

Should EV charging be considered when rewiring?

Yes. A charger needs its own circuit from the consumer unit with the right cable size; planning it during the rewire avoids pulling cables later.