When is Rewiring Necessary?
If a property has not already been rewired within the last 25-30 years, the chances are it will need upgrading at least in part in order to bring it up to current standards.
If you plan major remodelling work that constitutes a material alteration as defined by the Building Regulations, it is likely that you will need to rewire part, if not all, of the property, including upgrading the consumer unit (fuse box).
If you are extending your home, or converting an attic or garage, this will constitute new work and therefore all of the new wiring will have to conform to Part P: Electrical Safety, and all existing wiring will have to be improved to ensure that it is able to carry the additional loads safely, it is earthed to current requirements and that bonding is satisfactory.
Where you are extending or remodelling, the rest of the existing wiring does not have to be upgraded, except where upgrading is required by the energy efficiency requirements of the Building Regulations, i.e. central heating controls.
How to Tell if Your Property has Been Rewired
You should be able to tell if a house has been rewired recently by inspecting exposed parts of the wiring and by the electricity meter and fuse box (now known as the consumer unit). You can ask to do this when being shown around a property you are thinking of buying, or by inspecting your home. If there is an old-fashioned-style fuse box, with big white ceramic-style fuses, then the chances are that the property needs completely rewiring.
With two or more sets of circuits, it can be very difficult to know if all of them have been disconnected when undertaking work and this is unsafe. Another tell-tale sign that a rewire may be necessary is a mix of different socket and switch styles. This could indicate that a partial rewire has taken place, especially if there is evidence of surface-mounted wiring running along skirting boards and up walls.
In some rare cases of properties that have not been renovated in decades, you may still find example of old round pin sockets or original dolly switches, both of which are a sure sign that a rewire is necessary.
Another clue is the colour and style of the cabling, which you should be able to see at light fittings, around the fuse box. Modern electrical installations are wired in PVCu insulated cable coloured grey or white.
What if it has not Been Rewired?
Unless the wiring is the modern PVCu coated type, then a rewire is likely to be necessary. If you see any old rubber insulated cabling, fabric insulated cabling (used until the 1960s), or lead insulated cabling (used until 1955) then it needs replacing as the insulation can rot and/or break down, leading to short circuiting: a fire hazard and potential electrocution.
Even older PVCu cable may need replacing if it is not twin earthed cabling (with a second earth cable running within the outer sleeve), but this may only be evident if you are able to remove a switch or socket faceplate and look closely.
Checking for this conducting the viewing, and certainly is not advisable unless you are able to turn off the mains first.
If you are in any doubt, assume that a total rewire is required and budget accordingly. It may be that the system can be improved for less money by upgrading earthing and cross bonding.
If you proceed with the project, then before exchanging contracts you can arrange to get a qualified electrician to do a survey and find out exactly what work is required.
An electrician will typically charge £100-150 for a survey with a verbal report.
A full electrical survey with a written report is likely to cost £250-350.
A full rewire will cost around £2-2,500 for a small property and considerably more for a larger property, not including the cost of making good the decoration.
Very often, a full rewire can be avoided, however; providing the existing cabling is sound and able to carry any additional loads, it also may be possible to upgrade it by adding a modern consumer unit, proper earthing arrangements and cross bonding.
If rewiring work is required, it should be undertaken at first fix stage (before plastering), at the same time as any central heating and plumbing work. New cabling cannot be surface mounted and so the installation will involve lifting the floor coverings and floorboards and possibly , routing out channels in the walls and possibly in some ceilings that are inaccessible from above. All of this work will cause major disruption and so it is best not to try and live around the work if possible.
As well as installing new cabling, first fix stage will involve fitting new back boxes for all sockets and switches. In addition to rewiring for all power and lighting circuits, it is a good opportunity to rewire for modern central heating controls, alarms, smoke detectors and doorbells, and to rewire the telephones and television aerial sockets. It is also worth redesigning the wiring plan for sockets and switches to make sure it meets your needs and those of modern housebuyers.
Think about specifying two-way or even three-way switching for hallways and landings and other rooms with more than one main access. For a high-value property, consider adding a separate 2 amp circuit with separate switching for table and standard lamps in the main living rooms and principal bedrooms. It may also be worth considering adding automated lighting, home network cablings, speaker cabling and other modern technology.
If the mains connection and meter needs moving, this will have to be undertaken by the local electricity utility company. There will be a charge and several weeks notice will be needed.
Once the first fix stage has been completed, the property can be re-plastered or the walls and ceilings filled and made good, and the flooring replaced. The second fix work can then proceed fitting sockets and switch plates, light fittings, the consumer unit and wiring any electric fans, cookers, extractor hoods, electric showers and the immersion heater, if there is a hot water storage cylinder.
If you are working on a period building using vernacular materials, such as oak frame, cob or solid stonework, make sure your electrician is aware of this and has worked on such buildings.
Checking Earth Bonding
Earth bonding, also known as equipotential bonding and cross bonding, is essential for any electrical installation to be safe. Even if your renovation project does not require rewiring, make certain that the kitchen and bathrooms are earth bonded. Earth bonding will ensure that if a fault should occur causing the metal plumbing, bath, taps, radiators or boiler casing to become live, i.e. for current to flow through them, this will not lead to electrocution.
The reason the lack of earth bonding is often missed is because it does not affect the functioning of the electrical circuits in the house. To see if your project has been earth bonded, look underneath the sink or bath for metal clamps around the copper pipes with green and yellow striped earth cable attached. All pipes in and out of the boiler and heating systems need earth bonding.
If you are building with plastic pipe instead of copper, you do not need to earth appliances but you have to earth the mains stopcock. If this is not the case, then arrange for this work to be done it is a crucial safety requirement.
Electrics in Wet Areas
There are special restrictions on electrical work in wet areas where there is the greatest danger of electrocution. No power sockets are allowed other than shaver sockets, which must be located away from the splash zone from showers. Switches within a bathroom should be pull-cord operation, or IR-type switches powered by battery or with just a very lowvoltage signal cable, such as Cat5e.
Electrical appliances to be used in wet or damp places (except shaver points), including electric showers, light fittings and ventilation fans, must have levels of moisture and mechanical protection, known as IP or Ingress Protection numbers. The IP rating has the letters IP followed by two characters. The first specifies the degree of protection against particles or solid objects. The second specifies the degree of protection against liquids.
The I.E.E. Wiring regulations (BS 7671: 2001 Section 601) has mandatory requirements for areas containing a bath or shower. These safety standards are measured in zones, with the requirements for each zone being based on the perceived degree of risk of electric shock. There are four zone categories: 0, 1, 2 and 3.
Zone 0: Inside the bath or shower. Any fittings used here must be SELV (max 12V) and be rated IPX7 (protected against immersion in water).
Zone 1: Above the bath or shower to a height of 2.25m. A minimum rating of IPX4 is required.
Zone 2: The area stretching to 0.6m outside the bath or shower and above the bath or shower if over 2.25m. An IP rating of at least IPX4 is required.
Zone 3: Anywhere outside zones 0, 1 and 2. Where water jets are not to be used for cleaning purposes, the general rules of BS7671 apply. For detailed information, refer to the I.E.E. Wiring regulations (BS 7671: 2001 Section 601).
For the latest I.E.E. regulations visit www.theiet.org