Domestic Rewire Guide for Electricians

A domestic rewire involves replacing all or a significant portion of the fixed electrical wiring in a property. It is one of the most substantial jobs a domestic electrician undertakes, and getting it right requires thorough planning, skilled workmanship, and comprehensive testing.

Not every property needs a full rewire. Many installations can be upgraded, extended, or repaired without replacing all the wiring. However, certain signs indicate that a full rewire is necessary.

Signs That a Property Needs Rewiring

• ✓The wiring is over 25 years old and has never been upgraded
• ✓Rubber-insulated or lead-sheathed cables are present (common in pre-1960s properties)
• ✓The property still has rewireable fuses with no RCD protection
• ✓An EICR has returned an unsatisfactory result with multiple C1 or C2 codes
• ✓There is evidence of overheating at connections or accessories
• ✓The installation uses round-pin sockets or other obsolete equipment
• ✓Cables are degraded, brittle, or damaged
• ✓There is no earthing conductor in the cables (older installations)

Before starting any rewire, a thorough survey is essential. This determines the scope of work, allows you to provide an accurate quotation, and identifies any complications.

What to Assess During the Survey

• ✓The age and condition of the existing wiring
• ✓The type of construction (solid walls, cavity walls, timber frame)
• ✓Access routes for cable runs (under floors, through ceiling voids, in walls)
• ✓The location of the incoming supply and meter
• ✓The earthing arrangement and condition of the earthing conductor
• ✓The number and position of existing circuits and accessories
• ✓The customer requirements for additional circuits, sockets, or lighting
• ✓Any special locations (bathrooms, kitchens, outdoor supplies)
• ✓The condition of the existing main bonding

The survey is also your opportunity to discuss the specification with the customer. This includes the number of socket outlets in each room, lighting preferences (ceiling roses, downlights, dimmers), any specialist requirements (home office circuits, EV charging preparation, home cinema), and the consumer unit type.

First fix is the most labour-intensive and disruptive stage of a rewire. It involves running all the new cables through the building structure and installing back boxes for socket outlets, switches, and other accessories.

Cable Routes

Cables must be routed within safe zones as defined by BS 7671 Regulation 522.6. In walls, this means running cables vertically or horizontally from accessories, within 150mm of the ceiling or floor, or within 150mm of the edges of walls, doors, and windows.

First Fix Activities

• ✓Chasing walls for cable runs in solid walls (using a wall chaser or SDS drill)
• ✓Drilling through joists for cable routes under floors and through ceilings
• ✓Installing back boxes for socket outlets, switches, and fused spurs
• ✓Running cables from the consumer unit to each accessory position
• ✓Installing ceiling rose or lighting junction box positions
• ✓Running cables for specialist circuits (cooker, shower, immersion, outdoor)
• ✓Installing conduit or trunking where required
• ✓Leaving sufficient cable at each point for termination during second fix

Second fix takes place after the plasterer has made good the chased walls and any building work is complete. This is the stage where the installation is completed and tested.

Second Fix Activities

• ✓Installing and wiring the consumer unit
• ✓Fitting socket outlets, switches, and other accessories into their back boxes
• ✓Connecting and fitting light fittings, ceiling roses, or downlights
• ✓Wiring and connecting the cooker connection unit or cooker switch
• ✓Connecting the immersion heater, shower, and other fixed appliances
• ✓Installing extractor fans and connecting to switched fused spurs
• ✓Fitting outdoor accessories and weatherproof enclosures
• ✓Making all final connections and checking polarity

Testing and Certification

After second fix, the entire installation must be tested in accordance with BS 7671. This is a comprehensive process covering:

• ✓Continuity of protective conductors (R1 + R2)
• ✓Continuity of ring final circuit conductors
• ✓Insulation resistance (minimum 1 megohm between conductors)
• ✓Polarity at every accessory
• ✓Earth fault loop impedance (Zs) at the furthest point of each circuit
• ✓RCD operation time and rated residual operating current
• ✓Prospective fault current at the origin of the installation
• ✓External earth fault loop impedance (Ze)

Once all tests are satisfactory, an Electrical Installation Certificate (EIC) is issued. This certificate, along with the schedule of inspections and schedule of test results, is provided to the customer and notified through your competent person scheme.

A modern domestic rewire for a three-bedroom house will typically include the following circuits. The exact specification depends on the property size and customer requirements.

Standard Circuits

• ✓Ground floor ring final circuit (2.5mm T&E, 32A MCB)
• ✓First floor ring final circuit (2.5mm T&E, 32A MCB)
• ✓Ground floor lighting circuit (1.0mm or 1.5mm T&E, 6A MCB)
• ✓First floor lighting circuit (1.0mm or 1.5mm T&E, 6A MCB)
• ✓Cooker circuit (6mm T&E, 32A MCB for standard cooker)
• ✓Shower circuit (10mm T&E, 40A or 50A MCB depending on shower rating)
• ✓Immersion heater circuit (2.5mm T&E, 16A MCB)
• ✓Smoke alarm circuit (1.5mm T&E, 6A MCB)

Additional Circuits Often Requested

• ✓Kitchen appliance circuit (additional radial for dishwasher, washing machine)
• ✓Home office dedicated circuit
• ✓Outdoor power supply (for garden lighting, shed, etc.)
• ✓Electric vehicle charging point preparation (10mm cable to garage or driveway)
• ✓Loft circuit (for storage lighting and socket)
• ✓Garage supply

A three-bedroom semi-detached house typically follows this timeline for a full rewire:

Day 1-2: First Fix (Ground Floor)

Chase walls, drill joists, run cables, and install back boxes for the ground floor circuits. The ground floor lighting and power circuits are cabled. Any outdoor circuits are run during this stage.

Day 3-4: First Fix (First Floor)

Complete the first fix on the first floor, including bedrooms, bathroom, and landing. Run cables from the first floor back to the consumer unit position. Install smoke alarm cabling.

Day 5-6: Second Fix

Once the plasterer has made good (which may require a gap of a few days between first and second fix), install the consumer unit, fit all accessories, connect light fittings, and make all final connections.

Day 7: Testing and Certification

Carry out full initial verification testing, document all results, issue the Electrical Installation Certificate, and demonstrate the installation to the customer.

Understanding the different cable types and their applications is fundamental for any rewire. The primary cable type used in domestic installations is Twin and Earth (T&E), but others are used for specific applications.

Twin and Earth (T&E) — 6242Y

The standard cable for domestic wiring. Available in various sizes from 1.0mm to 16mm. Contains a line conductor (brown), neutral conductor (blue), and an uninsulated circuit protective conductor (CPC) which must be sleeved with green and yellow sleeving at terminations.

Three-Core and Earth — 6243Y

Used for two-way switching and other applications requiring a third conductor. Contains three insulated conductors plus an uninsulated CPC.

Flex (Flexible Cable)

Used for final connections to light fittings, appliances, and other equipment that requires flexibility. Must be appropriately rated for the application and connected using suitable termination methods.

SWA (Steel Wire Armoured)

Used for outdoor underground cable runs, such as supplies to outbuildings or garden lighting. The steel wire armour provides mechanical protection. SWA cable must be properly terminated using glands that maintain the earthing continuity of the armour.