- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 10 Aug 2018
When renovating a property, it is important to ascertain as early in the process as possible, whether rewiring will be required, as the fabric, décor and fittings of the building are likely to be disrupted.
Rewiring will usually be necessary if a building has not been rewired within the last 25-30 years. It may also be appropriate if major remodelling work is being undertaken such as building extensions or conversions.
|Reasonable provision shall be made in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installations from fire or injury.|
Old and out-dated round-pin sockets or dolly switches will be an indication that rewiring is required. The colour and style of cabling is another indication of rewiring. Modern installations are wired in PVCu insulated cable and are grey or white, while older wiring may be rubber, fabric or lead insulated. PVCu cables should be inspected, as older installations may not have twin-earthed cabling (i.e. a second earth cable running within the outer sleeve). A modern consumer unit will be fitted with miniture circuit breakers (MCBs) and residual current devices (RCDs).
 Rewiring process
It is important to have a general idea of room layouts before rewiring a building, so that lights, plugs and other electrical items can be positioned appropriately. The purpose of the rooms in terms of lighting, tasks, fire safety, security, and so on, should be considered at this stage. Having to make additions and amendments later is often costly and time-consuming.
It is also sensible to consider ‘futureproofing’ the installation to a certain extent. Will likely technological developments place additional demands on the building, such as Ethernet cables in every room to accommodate uninterrupted WiFi for new smart appliances? Are the requirements of the building occupants likely to change in the future?
For hallways, landings and rooms with more than one access, there may be a requirement for two- or three-way light switching. Other modern features that can be planned for might include automated lighting, home network cabling, speaker cabling, security cabling, heating controls, sensors, door bells, telephone and data, TV aerial sockets, and so on.
If the building is older or uses materials, such as timber panelling, cob or solid stonework, this should be communicated to the electrical contractor before work begins, as it can impact upon the techniques adopted and procedures followed.
The time taken will also vary, although the same size house might take around four or five days.
First fix is generally taken to mean the works before plastering. Running new cabling will involve lifting floor coverings, floorboards and possibly skirting boards, as well as routing out channels in the walls. First fix work also involves fitting new back boxes for sockets and switches.
- Fitting sockets and switch plates.
- Installing light fittings.
- Installing the consumer unit.
- Connecting kitchen and bathroom fittings (electric fans, cookers, extractor hoods, showers, immersion heater, and so on).
 Earth bonding
Earth bonding (also known as cross bonding) ensures that if a fault occurs which causes metal components (such as plumbing, boiler casing, radiators and so on) to become live, they do not pose an electrocution hazard.
Underneath sinks or baths, metal clamps will often be placed around the copper pipes with green-and-yellow striped earth cables. All pipes leading to and from the boiler and heating systems need earth bonding. Buildings using plastic instead of copper pipes require the mains stopcock to be earthed rather than appliances.
Wet areas offer the greatest risk of electrocution and so extra precautions are necessary. Sockets for shavers are permitted away from bath and shower splash zones, but no other power sockets. Switches should be pull-cord operation or battery-powered IR-type switches.
There are mandatory requirements for areas containing a bath or shower, as specified by the I.E.E. Wiring regulations (BS 7671: 2001 Section 601). Safety standards are measured in zones, with the perceived risk of electric shock being the basis of each zone’s requirements. The zone categories are as follows:
- Zone 0: Inside the bath or shower. Any fittings must be SELV (max 12V) and rated IPX7 (protected against water immersion).
- Zone 1: Above the bath or shower to a height of 2.25 m. Minimum rating IPX4 required.
- Zone 2: Area reaching up to 0.6 m outside the bath or shower. Minimum rating IPX4 required.
- Zone 3: Area outside above zones. General rules of BS 7671 apply.
 Electrician or DIY
Part P of the building regulations covers electrical works. While minor repairs, replacement and maintenance work are not notifiable, more significant works, and work in wet areas may be require a Building Regulations application, with the work inspected before and after completion by a qualified electrician. The electrician will check compliance and issue a part P certificate.
Approved document P makes clear that after the works are complete, the installation should be no more unsatisfactory that before the work was started. When extending or altering and installation, only the new work must comply with the building regulations, unless:
- The new work affects the safety of the existing installation, or;
- The condition of the existing installation means that the new installation cannot be operated safely.
Attempting electrical works as a DIY job, can be a false saving, and can result in dangerous defects. A common DIY fault is running the cable at angles across walls. This is in contravention of wiring regulations which require all cables buried in walls to run vertically or horizontally from sockets.
- How long they expect the work to take.
- The number of circuits.
- The number of power points, light fittings and switches.
- Whether work is new build or extension.
- Whether there is a lot of preparatory work required such as chasing out plasterwork, lifting floorboards, and so on.
- The specification of switches, sockets, and so on.
 Find out more
 Related articles on Designing Buildings Wiki
Featured articles and news
Achieving an alternative route into the profession.
Why construction is so corrupt.
Restoration of Alfred Waterhouse’s Manchester Town Hall.
Widening access to hidden architectural treasures.
A material with exciting potential.
ECA-partnered survey shows the clear benefits.
Hire for potential, not competence.
A single knowledge hub for global infrastructure.
Compliance in construction.
The growth of the smart homes market.
Giving professional advice to friends.