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Partial Rewire & Circuit Extension

Upgrade specific circuits without a full house rewire. Ideal for extensions, old lighting circuits, or outdated ring mains. Qualified and insured.

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Partial Rewire & Circuit Extension

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NICEIC & NAPIT registered.

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How it works

1

Assessment and scope

The electrician inspects the circuits that need replacing and the overall condition of the installation. They define the scope of work — which circuits will be replaced, what new circuits are needed, and whether the consumer unit needs upgrading to accommodate the changes.

2

Circuit design

New circuits are designed to BS 7671 standards. Cable routes are planned to minimise disruption. If new sockets or lighting points are being added, positions are agreed with you. The electrician confirms whether the existing consumer unit has capacity or if a new board is needed.

3

First fix — cabling

Old cables for the affected circuits are removed. New twin-and-earth cable is routed through the property — chased into walls, run under floors, or through ceiling voids. Back boxes are installed for new accessory positions. Disruption is limited to the affected areas only.

4

Second fix — accessories and connection

Once any plastering is complete, faceplates, switches, and other accessories are fitted. New circuits are terminated at the consumer unit. If additional ways or a new board were needed, these are installed at this stage.

5

Testing and certification

All new and affected circuits are fully tested to BS 7671 standards. An Electrical Installation Certificate (EIC) is issued for the new work. The electrician also checks that the new circuits integrate safely with the existing installation. The work is notified to Building Control via the competent person scheme.

What's included

Removal of old wiring on affected circuits
Supply and installation of new twin-and-earth cabling for specified circuits
New sockets, switches, and accessories where required
Additional ways in the consumer unit or new board if needed
Appropriate circuit protection (MCBs, RCBOs) for new circuits
Earthing and bonding upgrades where required
Full testing of new and affected circuits to BS 7671
Electrical Installation Certificate (EIC)
Part P Building Control notification

What's involved

A partial rewire replaces specific circuits or sections of wiring in a property rather than the entire installation. This is common when extending a property, upgrading a single floor, replacing a deteriorated lighting circuit while the socket circuits are still sound, or bringing the wiring in an extension or loft conversion up to current standards. The new wiring is connected to the existing consumer unit (or a new one if needed) and fully tested and certified.

Not every property with electrical issues needs a full rewire. If an EICR identifies problems on specific circuits — for example, an old lighting circuit with rubber-sheathed cable while the ring mains are fine — a partial rewire targets just those circuits. It is also the standard approach for extending the electrical installation into a new extension, loft conversion, or garage conversion. Partial rewiring is notifiable work under Part P and must be carried out by a registered electrician.

Get a personalised quote

Typical cost: £1,000–£4,000depending on scope

Every job is different — pricing depends on your property, location, and specific requirements. Describe what you need and a qualified electrician will quote you directly.

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How long does it take?

1-3 days for a single circuit or small scope. 3-7 days for multiple circuits or a full floor. Second fix is typically a separate visit after plastering. An extension rewire usually takes 2-4 days for first fix.

Regulations & safety

Safety notice

Partial rewiring is notifiable electrical work under Part P. Even if you are only replacing one circuit, it must be designed, installed, and tested by a qualified electrician registered with a competent person scheme.

Connecting new wiring to old wiring requires careful assessment. Incompatible cable types (e.g., joining modern PVC cable to old rubber-sheathed cable) can create high-resistance joints and fire hazards. Your electrician must ensure all connections are safe and compliant.

If your consumer unit does not have RCD protection, adding new circuits may require upgrading the board. This is a safety requirement — do not allow new circuits to be connected to an unprotected board.

Part P of the Building Regulations (Approved Document P)

Adding new circuits or replacing existing circuits is notifiable electrical work. The work must be carried out by a registered electrician or inspected by Building Control.

BS 7671:2018+A2:2022 (IET Wiring Regulations, 18th Edition)

All new wiring must comply with the current edition of the Wiring Regulations, including cable sizing, circuit protection, earthing, and special location requirements.

Building Regulations Part L (Conservation of Fuel and Power)

If the partial rewire is part of an extension or conversion, the electrical installation must also comply with energy efficiency requirements, including provisions for energy-efficient lighting.

What to expect

The cost varies enormously depending on scope. Replacing a single lighting circuit in a two-storey house might be £1,000-1,500. Rewiring an entire floor or adding circuits for a large extension could be £3,000-4,000. Get a clear written quote with a defined scope of work.
A partial rewire causes less disruption than a full rewire, but there will still be chasing, dust, and some floorboards lifted in the affected areas. If the work is on a ground floor, the first floor is usually unaffected and vice versa.
Where new cables meet old, the junction must be accessible and properly made. Your electrician may recommend replacing a slightly wider scope than strictly necessary to avoid problematic junctions — this usually adds modest cost but improves long-term reliability.
If your EICR shows the lighting circuits need replacing but the ring mains are fine, a partial rewire is typically the right approach. However, if the ring mains also show signs of deterioration, it may be more cost-effective to do a full rewire now rather than returning in a few years.

Having issues with your existing installation?

Already have a partial rewire & circuit extension and having issues? Check our troubleshooting guides.

Wiring Concerns & Issues

Old Cloth Or Rubber Wiring

Your home has old cloth-insulated or rubber-insulated wiring that is deteriorating and may be unsafe.

Frequently asked questions

What is the difference between a partial rewire and a full rewire?
A full rewire replaces all the wiring in the property. A partial rewire replaces only specific circuits or sections — for example, just the lighting circuits, just one floor, or just an extension. The choice depends on the overall condition of the wiring, identified by an EICR.
Can old and new wiring be safely connected together?
Yes, if done correctly by a qualified electrician. The key is that the junction between old and new cable must be accessible, properly enclosed, and the old cable must be in adequate condition. If the old cable is deteriorated, the connection point is moved back to where the cable is sound.
Do I need a new consumer unit for a partial rewire?
Not always. If your existing consumer unit has spare ways, adequate protection, and meets current standards, new circuits can be added to it. However, if the board is old, has no RCD protection, or has no spare capacity, an upgrade will be recommended as part of the work.
Is a partial rewire cheaper than a full rewire in the long run?
It depends on the condition of the remaining wiring. If only one or two circuits need replacing and the rest are sound, a partial rewire is significantly cheaper and makes good sense. If the remaining circuits will need replacing within 5-10 years, a full rewire now is usually more economical.
Will I need to redecorate after a partial rewire?
Yes, in the affected areas. Cables are chased into walls, which need replastering and redecorating. The disruption is limited to the rooms and routes where new cables are run. Unaffected rooms will not need any work.

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Sources & References

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