Basic principles for supply and load
With a brownfield development site, it is possible that you may have a live electrical supply which can be temporarily disconnected, an interim supply provided for your contractors and then a final connection made again when the new property is completed. However, for all other sites a new supply is going to be needed. The UK is divided up for electrical distribution and in your area, there will be one regional monopoly known as a Distribution Network Operator (DNO) which is responsible for existing and new supplies. An application must be submitted for a new connection which will involve the DNO providing a physical connection from their main supply (usually in the nearest highway) to your site which will then give you a Meter Point Administration Number (MPAN). These supplies are quoted individually, likely to start from circa £1,200 and do not include the cost of digging trenches on your site or building meter box housings, temporary or otherwise, which have to be provided by you or your contractor. It’s a regulatory service so each DNO has a code by which they must operate one of which is time. Usually the works are carried out with 6-8 weeks from payment, and payment can only be made once you have completed an application and had a fixed quote, which may have to follow a site visit. So, allow about 4 months for the whole process. Thereafter you are free to choose an electricity provider who will fit a meter (usually FOC) and charge you for your consumption moving forward.
The DNO will however have to put a supply in to you site capable of delivering your anticipated load. An electrician will help you calculate this and, depending on your anticipated demand, may involve a three-phase supply which will cost you more but deliver a higher output for the same typical infrastructure. Electrical load will be significantly influenced by things like electrical heating but also, distance to the site and, for bigger houses with plenty of outbuildings, the physical number of outlets for lighting, power and other services. The UK electrical voltage is 230V and the flow rate (or current) through the circuit is measured in amps. The output, i.e. the work that the electricity does as it flows through your circuits, is measure in watts. Typically, a house supply will be controlled by switchgear after the meter set to a 100-amp rating which means that your overall load to the property, at any one time of maximum use, would be 23 KW (100A x 230V). In order to regulate use at the property to ensure that you don’t exceed this maximum load, your consumer unit (old fuse board) will have individual miniature circuit breakers (MCB’s) which manage the overall load on each individual circuit.
The regulations and who can do what work
Electrical installations in domestic properties has also been more heavily regulated since 2005 when Part P of the Building regulations was first introduced. This obligates the building owner to either have their electrical work carried out by a competent (qualified) electrician who can self certify as necessary, or to arrange for compliant testing and certification through Building Control which will probably involve another competent electrician testing the installation when it has all been completed. Either way, certificates are required to demonstrate that the installation is in accordance with the latest IEE wiring regulations (BS 7671).
Typical budgets for electrical works
In 2015, we completed the Built It Model House costs summary where a relatively typical 155m² two-storey house had electrical costs of circa £10,500 plus an additional £1,500 for the main connection which represented about 5% of the overall building budget. Of course, there’s a huge number of variables which could affect this but, as a starting, point these metrics are a useful guide. There’s a lot of specialist equipment to use and many electricians are also wedded to their own supply as they have confidence through experience in certain manufacturer products. Products which you could consider purchasing yourself would be the light fittings, face plates, extractor fans, alarms, aerials, satellite etc., but unless you are aggressively managing your project through material supply deals, you could find it a lot easier to leave your electrician to supply everything else.
The consumer unit and installation safety
You’ll need to plan the entry point for your supply and meter location close to where you anticipate having the fuse board (now known as the consumer unit) as these two should be in close proximity (several meters maximum). Most new houses use proprietary white meter boxes which get built into your external wall for easy access for meter readings from the outside. If you have a long drive, you may choose or end up with a detached meter housing (brick and tile built) by your gate, with the 100 A fuse before an armoured cable then runs the length of the drive to the house.
The consumer unit is the control centre for the individual circuits for lighting, power, external supplies, the garage, alarms etc. It is racked out with MCB’s all of which will be rated in amps for the circuits they are to control. In addition, however, these MCB’s will now be protected by an RCD (Residual Circuit Device) which is there to immediately switch off the current in the event of a fault, usually known as earth leakage. As these can be sensitive, the normal installation has two RCD’s with half the MCB’s on each one. Usually upstairs lighting and downstairs power are protected by one and the downstairs lighting and upstairs power on the other, so that you are not completely plunged into darkness when/if a fault materialises. So, in summary, discuss the consumer unit layout with your electrician so that you are happy with its location, height, access and general arrangement. The MCB’s are there to protect against fire through overload on the system and the RCD is there to protect against shocks through leakage of supply to earth (i.e. potentially you!).
Lighting considerations
Lighting is much more than illumination and will also end up affecting the overall mood of the house. If you need help then an experienced interior designer can add huge value here. All new lighting now will be low energy which means lower rated (LED) lamps which burn just as brightly for significantly lower watts. This means less current is required which means more lights could go on a typical circuit. Low voltage lighting is used in bathroom locations as a safety measure to reduce the risk of a shock. The voltage is transitioned down locally by the local transformer which may serve one or more lamps.
LED lamps come in a raft of options. Light output is measured in lumens but the colour (from icy cool blue to warm orangey yellow) is measure in kelvins. They can be dimmable and set at predetermined levels as part of a smart lighting install. Many people love the idea of smart lighting but equally others have tried it and ended up being frustrated with the slow response and indefinite switching. Its quite an expense so you would be wise to proceed only if you really want this level of functionality.
External lighting will need its own circuit, properly protected with appropriate cable and fittings. However, an external light on an outside wall can often be included on an internal lighting ring with a fused spur. Two, three and four-way switching for lights is easy to organise at the outside but a real pain for the electrician to introduce retrospectively so think this through carefully. Low level night lights on landings, activated by movement are also stylish and helpful, especially with younger children.
Power circuits and heavy use items
Power circuits are delivered in rings (circuits) using thicker cable as they carry higher loads than lighting. You should be able to have as many sockets as you want in a continuous ring, but where a radial circuit has been used (one way only) there are more stringent limitations. The area covered and the length of the ring is also a size restrictor. Certain power items require their own supply due to the really heavy load, i.e. your electric cooker, an immersion heater in your hot water cylinder or an electrically operated shower. There was much consternation about socket positions having to be a minimum of 450mm off the floor when this was introduced 15+ years ago (Part M of the Building regulations) but generally this has been warmly welcomed as users realise that sockets at more convenient locations makes huge sense. Have fun in thinking through where you will want your sockets located and, if in any doubt, add another one in.
Other items not to forget
A full electrical installation will include much more than just lighting and power circuits. Items which are often not thought through early enough include: Cat-6 cable for audio visual distribution, hidden speaker cables, coaxial cable for aerial distribution, smoke and heat detector locations, security alarms including wall PIR and window/door sensors, bathroom electrical under-tile heating, and ventilation. Local fans don’t need to be noisy anymore and you can get good continuous and healthy operation from centrally controlled units instead.
External works should also be planned at an early stage with armoured supplies going to satellite buildings which should have their own smaller consumer unit installed. And don’t forget supplies for BBQ sockets, drive way lighting, electric gates and sewage treatment tanks amongst others!
Mark up your plans
By far the best way to avoid budget shocks is to think through your requirements at an early stage and to mark up a plan neatly to share with your contractor(s). There are specific symbols for electrical notation on professional architectural plans but you can simply use different colours to represent lighting, power, comms, etc on your plans. Once done you can quantify the number of lighting and socket points and all other items and reproduce this in a schedule so that the electrician and /or the main builder can price your works more accurately. If you choose not to do this (the majority!) then you builder will price your project with a provisional sum for the electrical installation and the full cost of the electrical works will only become known when you first walk through the building with your installing electrician.
Additional considerations for refurbishments and/or extensions
For refurbishment projects or extensions, it may be possible to limit the disruption involved and/or, at the very least, act more strategically regarding replacement access. A full house rewire will require access to the 1st floor intermediate floor-zone for ground floor lighting and first floor power and, dependent upon your ground floor construction type, you may also choose to manage the ground floor power with top down wiring. Then, once the flooring is put back, access to the attic void will be necessary for 1st floor lighting and attic power/lights. Cables are normally run leaving the original installation intact and then, once all of the new installation is complete, the old network is switched off, the new one livened up and the old installation carefully removed. Extensions, depending on size, can often be managed by adding new ring circuits to the existing consumer unit. But in reality, many extensions also end up triggering fundamental upgrade to the existing and, thus, a new consumer unit as well.
Written and published in August 2017
