Rewiring Tips

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Revision as of 18:14, 11 February 2007 by (talk) (→‎MCB Type)
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Lots of useful information for anyone due to rewire.

The basic electrical installation design is fairly much decided by the 16th edition wiring regs, so unless you get into specialist, unusual or illegal territory, many of the choices are already made for you.

You're still left with quite a lot of details to choose from. These details can affect comfort, safety, reliability, and avoid unnecessary trouble and expense. In sum these many details can make quite a difference. A lot of good choices can be made at little or no cost, and several will save money.

The Basic System

You'll get 30A rings supplying the sockets, or occasionally 20A radials. You'll get 6A lighting circuits, or occasionally 10A. You'll get dedicated feeds for cooker and shower if you've got those, or the oven might end up on a 13A plug.

You'll usually get 1 RCD, which in a minority of cases can produce a lot of frustration by frequently taking out the power.


CU: consumer unit, the modern version of a fusebox.

Split load CU: A CU divided into 2 halves, each with its own main switch. A good idea. It means power can stay on no matter what happens to one section of the wiring. Even during a partial rewire half the power can stay on.

MCB: a pushbutton overcurrent trip found in the consumer unit. This replaces a fuse. Rewirable fuses are still fully compliant with today's wiring regs. Contrary to popular myth, MCBs are not a significant safety benefit for general use, but they are easier to reset. Where they are a safety plus is when householders can be expected to be irresponsible, eg rented property. MCBs should be chosen in these cases, as rewirable fuses are easy to abuse.

RCD: earth leakage trip found in the consumer unit. This will trip if earth leakage current is too high, and reduces the risk of electrocution. Unfortunately they're known for nuisance trips. The majority of older installs have no RCD.

TT: a type of earthing that uses a local earth rod. TT installs must have a whole house RCD, since an earth rod alone is inadequate to clear faults. Whole house RCDs should be avoided with other installation types, as they're a known source of problems.

The Choices

Now some ideal choices. Many will add a bit to installation cost, but are well worth it. Many cost nothing extra, and a few cost a lot. One can make many good choices for as little as an extra £100 in total.

Split Load CU:

Use of a split load CU means one half of your wiring can be turned off while the other half stays on. So whatever may happen with your electrical system*, you dont need to turn it all off. This enables you to have power in the event of a fault, and to have power while working on the installation itself. Split load CUs are common today, just check you get one. Typical extra cost: £0

*there are exceptions, such as lightning strike or a major fire.


RCDs are almost universal in new installs. Unfortunately they're also a source of a good deal of trouble for a minority of householders.

What you don't want is the default install of one RCD supplying half or even the whole house. Most of these work OK, but some create no end of frustration, trouble and expense for the householder. For £35-£100 more you can have 2 or 3 RCBOs instead of one RCD, which eliminates many RCD nuisance trips, and minimises the consequences of any that do occur. This way if an RCBO trips, you lose power to one socket circuit instead of all power.

Unless you have a TT earthing system, lighting should not be on an RCD*. Lighting circuits have not proven to be a significant electrocution risk. RCDs tend to cause lighting to fail early in a fire, and this has resulted in the death of people failing to escape. Lighting is not usually on RCD**, but many such setups are in use.

* except that regs now mandate an RCDed feed for bathroom lighting on new installs

** except with TT earthing, where all power is fed via RCD.

Dedicated Freezer Feed

A freezer is best put on its own dedicated feed, so other appliance faults dont stop it working and ruin £££ of food and days of your cooking efforts. This is a much bigger issue with new rewires than it has been in the past, as RCDs are easily tripped.

Don't have any RCD on the freezer supply when possible. To meet 16th edn regs, this means the socket for the freezer should not be likely to be used by outdoor tools, so don't put the socket by the back door.


You need enough. Double sockets are not adequate by themselves to run the amount of electronics we use today (the last socket I put in was a 12 way). On the other hand, installing large numbers of fixed sockets is an eyesore and expensive. Doubles are enough if you sprinkle them around the room, and don't mind using several 4 & 6 way extension leads.

Halogen Lighting

I don't recommend halogen downlighters. They're expensive to run, are one of the most energy inefficient options available, heat the house up in summer, they make lying right back in your own home truly uncomfortable, and they tend to give uneven illumination and glare. Halogen lights are also the type most capable of starting fires, and most halogen downlighters pierce the ceiling plasterboard fire and smoke barrier.

Its wise to calculate run costs before installing halogen, to avoid regret. As an example, 500w of halo downlighters on 6 hours a day would cost £65 per year per room in electricity, plus 12-24 bulb replacements per year at £1 each, making a total cost of £77 per room per year. 4 rooms of this would equal £308 per year, or £9000 per 30 year product life*. The actual amount will depend how much you install. For some people that cost is fine, but for some its not the best way to spend the money.

For those tempted by halogen, I would suggest using lower power halogen downlighters, eg 5w, 10w or 20w, and making up the rest of the light level with better light sources, such as uplighting or concealed lighting.

Avoid mains voltage halogens below 150w. Mains bulbs are lower efficiency compared to low voltage ones, more fragile, shorter lived, and more susceptible to early failures. They're also more cost per bulb. For lights under 150w, always choose low voltage.

* Its actually more complex than that, the figure given just gives some idea of what those new halogen fittings will really cost.


Use switchbanks where possible. These are 2 or more switches in the one box, where one would traditionally find a single switch. Each switch controls some of the lighting. Thus it is easy to control lighting brightness. Cost is about £1 more per switch point, they typically save this much in under a year.

The easy ability to adjust brightness significantly improves both living comfort and utility, saves energy, and reduces cost of energy and hassle of replacement bulbs.

Using dimmers to achieve a similar result results in much greater electricity use, as bulb efficiency falls very rapidly with dimming.


Uplighting gives more even illumination, less shadows and dark spots. With white ceilings of at least normal height, uplighting is a good approach to general lighting.

If you want uplighting, I can recommend using spotlight fittings with ordinary GLS bulbs or CFLs in, not spotlight bulbs. The fittings need to shroud the bulb of course. For large uplighters, try PAR38 spotlight fittings that wrap around the bulb, again using GLS or CFL bulbs, not PARs.

Don't use those 'orrible plaster uplighters, they're inappropriate for uplighting. They create a high intensity light patch on the wall, which uplighting is intended to avoid. They light the wall from such a shallow angle as to magnify and illuminate even the tiniest blemish, making the wall look a mess.

Avoid halogen uplighters, they quickly ignite any paper or plastic that lands on them, or that they land on, and there are already too many deaths in house fires.

Kitchen worktop lighting

Mini fluorescent strips are a good idea, but are sometimes supplied with poor quality bulbs, such as 4000K. Fluorescent gives good even illumination, but don't go overboard on light level, and check the points above for a good fl lighting installation.

Halogen worktop lighting is prone to causing glare.

Tubular filament lighting is especially energy inefficient, and runs hot, often discolouring kitchen units and heating stored food. Tubular filament lights also have safety issues. As well as both ends being open to touch, one of which is live, if you touch one end of the tube while inserting the other you can get a shock, and this is easy to do if not paying full attention for a moment.

CFL worktop lighting is cheaper to install than linear fluorescent in cases where there is enough room to fit them. The lightspread is not quite as even as linear fl, but the end user can easily adjust the light level to suit personal preference by replacing bulbs.

Fluorescent Lighting

Fluorescent lighting can look good if chosen and installed well. But the all too common choice of a bare bulbed butt ugly glowstart fitting in the centre of the room with a tube chosen at random is a recipe for unpleasant lighting.

Good fluorescent lighting needs the following points:

1 Hidden fittings & hidden bulb.

2 Uplighting

3 comfortable light level.

4 No flicker and flash

5 A tube of respectable quality. I like 3500K tubes, there are several good types to choose from, but there are also many unpleasant or poor quality types of tube on the market.

6 Spare tubes of a size that makes keeping a spare practical.

For 1 & 2 - use trough fittings.

For 3 - Choose around a quarter the power you would use with filament bulbs.

For 4 - An electronic ballast fitting avoids all the flicker and flash of cheap glowstart fittings.

For 5 - see the next section

For 6 - 2 foot tubes are easiest to store, 4' are next best. I would not normally recommend larger tubes for domestic use.

Fluorescent tube types

There are many different versions of white, ranging from excellent quality to dire. Buying tubes at random is liable to give you unsatisfactory lighting. Tubes are normally marked with their colour on on the glass at one end. Many shop assistants are unaware that there are different versions of white, or that the tubes are thus marked, you generally have to look for yourself.

Tubes marked simply as 'white' are not of the best quality, though not the worst. I can recommend 2700K and 3500K tubes, but I don't recommend higher colour temperature tubes for household use.

2700K is the colour of GLS filament bulbs, so it matches perfectly with traditional filament lighting. 2700K is a warm slightly yellowy white.

3000K is the colour of halogen bulbs, cleaner and crisper than 2700K. Some 3000K tubes dont have good CRI*, so if you want 3000K to match halogen its best to pick the more expensive triphosphor tubes rather than halophosphates.

3500K will not match other light sources, unless theyre also 3500K fluorescent, but used alone they give a clean fresh and slightly cool look. These are my favourite halophosphate tubes for domestic lighting.

4000K look cold and anaemic, and 4500K and up are like the old fashioned 'cool white' tubes that once gave fluorescent lighting such a bad reputation.

There are also proprietary numbering systems, such as the Philips system.

'Cool white' and 'daylight' are unsuited to domestic use.

* CRI = colour rendering index, a measurement of how well fluorescent tubes render colour. 100 is perfect, 50 is pretty grim. Triphosphor tubes have higher CRI than halophosphate, but cost more.

For more information see Fluorescent Lighting

Filament Strip Lights

Do not install filament strip lights.

Filament strip bulbs are around a foot long, and rated 30w and 60w. These are very cheap to buy but have particularly poor energy efficiency, unnecessarily high run cost, and the bulbs need frequent replacement.

Both ends of the fitting are open to touch when the bulb is removed, one of which is live when on, and also sometimes live when off.

These lights also suffer from their own particular safety problem. When inserting a bulb, if you touch the end of the tube out of the fitting, you have a 50% chance of being personally connected to the mains. This is due to a few factors with these fittings that combine to make them unsafe.

There are 2 ways this can happen. Firstly relamping while switched on gives this scenario a 50/50 probability of causing electric shock, and its very easy to end up with a finger on the wrong part of the bulb, it only takes a brief moment of paying attention to something else.

Secondly, relamping is not always safe while switched off either, as the fittings often use non-polarised connectors with single pole switches as well as having the bare live end and conductive tube with separated connections problems.

Tubular filament lamps were in use before WW2, and should have been left there. Fluorescent strips will have much lower power ratings, since they're several times more efficient, and wont fry the kids.

Kitchen worktop lighting

Fluorescent gives good even illumination, but don't go overboard on light level, and check the points above for a good fl lighting installation.

Halogen worktop lighting is prone to causing glare.

Tubular filament lighting is especially energy inefficient, and runs hot, sometimes discolouring kitchen units and heating stored food. Tubular filament lights also have safety issues explained above.

CFL worktop lighting is cheaper to install than linear fluorescent in cases where there is enough room to fit them. The lightspread is not as even as linear fl, but the end user can easily adjust the light level to suit personal preference by replacing bulbs.

Stair Lighting

It is a wise idea to arrange stair lighting so that the failure of any one light does not jeopardise safety. Stairs cause many injuries & fatalities each year. If lights have overlapping lighting areas, the loss of one light is not a real problem.

Do not install stair lights out of reach, this is a recipe for a serious accident, inconvenient, and a poor design choice common in times past. It causes falls down stairs while replacing bulbs, delays in bulb replacement, and the elderly and chronically infirm are too often ripped off with exorbitant charges for simply replacing a lightbulb that they can't reach (eg £50 callout charge).

Connecting different stair lights to different lighting circuits ensures lighting stays in service if/when one of the circuits trips. When there is only one stair light, it can be connected to a different circuit to whichever other light fitting gives the most light to the stairs.

Emergency lighting

Stairwells with no windows benefit from battery backup lights as used for fire escape. Non-maintained units only come on when power is lost, and cost around £17 each.

Such a light fitted by the CU is also a nice option when money is no object, but a torch or candle fumbled for in the dark is cheaper.

MCB Type

Lighting can be on type C MCBs rather than the more common type B. Some installs suffer frequent nuisance trips when bulbs blow, the risk of this is a little lower with a type C MCB. Care should be taken to ensure the circuit is tested and figures compared with those in the current edition of BS7671 for maximum Zs. MCBs of either type cost around £6 each, and the average 2.5 bed house will have 2 or maybe 3 lighting MCBs. Larger buildings will have more.

Lighting circuits on rewirable or HRC fuses pretty much eliminate the false trip problem, but rewirable fuses can be abused by irresponsible people, so these are better avoided in rented accomodation, institutions, etc.

Light Switch Controls Plugged in Lamps

It is possible at extra cost to provide wall sockets powered by the wall lightswitch, so standard lamps and table lamps all switch off in one go. Due to technical issues these will usually be 2A or 5A round pin sockets.

You can either fit a round pin plug on the light or use a round to square pin adaptor. The latter are difficult to find, as they have not seen significant use in decades, but can be made from a plug, socket and flex.

2A plugs look nicer than 5A imho. 2A equates to a power limit of approx 500w per plug.

Cutting costs

If necessary, the cost of a professional rewire may be trimmed by the house owner cutting all the chases and routing all the wire as pencilled in by the electrician. For more serious savings, do the whole job yourself. News:uk.d-i-y can help explain things, and avoid common design mistakes. Its fair to say though that there are some folk that should not do it themselves.

Cost of Rewiring when Buying a House

Don't overlook the fact that channelling wiring causes considerable damage and mess, and requires redecoration. Don't forget to cost this in when buying a house.

Listed & Character Buildings

The damage caused by rewiring can sometimes be a real problem in listed, period & other character buildings. In these it is important not to damage or destroy features. In such situations it may be wise to use a written agreement regarding wire routing and damage with your installer. With listed buildings it may be wise to explain to your installer that damaging certain features could constitute a criminal offence. If in doubt about rewiring a listed building, consult your CO first.

When it is desirable to keep period electrical features, this can be done legally and safely, but it is not as simple as just connecting them up. There are a few ways to do it, but this is a subject for another article.

CFL Light Quality

CFL energy saving bulbs are available in a wide range of qualities. Some produce excellent quality light, copying filament bulbs faithfully, and are very long lived, some produce a pinkish so-so quality light, and some are simply unacceptable (often 6000K or more, and found in pound shops). This variation has led to a reputation for substandard light quality. Try different brands to see what's good, trying one of each initially. The other pitfall to avoid with CFLs is the misleading wattage equivalences quoted on the packs. Real power equivalence ratio is at best 4x, so ignore the pack claims and use 15-18w to replace 60w, and 25w to replace 100w.

Futureproof Fitting Choices

Pick light fittings that will take either GLS or CFL. That way there will be no need to replace light fittings, whatever the future may bring. CFLs are generally larger, and not all fittings will accommodate them. R80 spotlight fittings are not ideal: although available in CFL form, these CFLs are very expensive at over £20 a bulb. There are also £8 ones available, but these have lower light output, and are a bit larger, making the fitting look like the bulb is falling out as well as dim.

Bulb Bases, BC ES & Miniatures

ES screw in bulbs generally cost more than BC Bayonet bulbs, and ES are prone to jams and breakages, and very rarely, bulbs falling out. ES sockets also rarely kill people, whereas BC haven't so far. So BC is generally preferred.

Low power miniature base bulbs (SES, SBC, E14 etc) are generally higher priced than ES and BC, and not always as widely available, so are best only used when there is a reason for them.

SES and SBC lampholders must not be used on circuits >6A, so it's a good idea not to use 10A lighting circuits in dwellings as an unskilled person might fit an SBS or SBC decorative fitting at a later date. 6A mcbs with 1.5mm^2 cable (rated for >10A) gives you the best of all options.

Bulb selection

A good house lighting design will use a small variety of bulbs, making stock keeping easy. All will be easily obtained and easily stored bulb types. Ideally they will also all be low cost high efficiency types. Tubular filament bulbs, PAR38s and large fluorescent tubes (8', 5') will not be used. Nor will relatively uncommon sizes (6', 3')

Relamping Access

All fittings should be readily accessible so that relamping is easy and safe. The temporary loss of one light should not cause any safety problem or inconvenience.

Outdoor Security Lighting

A common mistake is to use a 500w halogen when 100w or 150w would be more appropriate. Blinding burglars does not seem to make them see the light.

Place your PIR light directly above the door rather than away from it. This way the visitor's face is lit, yours is not, and you're not looking towards a light bulb, but they are. This maximises your security on all 4 points.

If your door is a short distance from the pavement in town, use a PIR detector with a short range to avoid unnecessary repetitive triggering. If your door opens direct onto the pavement, but is set back a foot or more, use an infrared beam-break trigger rather than PIR or always on. If you have a porch that opens onto a pavement, putting a PIR high up inside the porch on the small sction of wall at the front can shield the pavement from its view.

Ideally position PIR sensors so they dont gaze at the sun, they don't look at lights they control, and approaching visitors walk across their field of view. If you don't meet these recommendations they will usually work, but sometimes performance problems can occur. If your situation means you have to ignore all 3 recommendations, it may work fine, but don't blame the manufacturer if it doesn't behave quite as well as expected.

Finally, don't forget to set the adjustments on a PIR once its installed. Sensitivity adjustment determines how close someone has to be before it triggers, and dawn/dusk adjustment determines at what daylight level it stops switching on. It is a little optimistic to expect units to come correctly pre-adjusted.

Tree & Shrub Lighting

Lights among clumps of bushes or up trees can be pretty, but the wiring is more expensive than putting it on the wall, and has more chance of failure. Halogen capsules should not be fitted near foliage, as halogen capsules run at very high temperatures and are a fire risk. Outdoor wire runs should be on their own circuit, with their own fuse or mcb & RCD. The reason for this is failure rates are higher than with indoor wiring, and wiring them onto existing indoor circuits can therefore cause trouble and expense.

CFLs outdoors

CFLs are generally ill suited to PIR use, but well suited to lights that stay on. When using CFLs outdoors, the type with their own built in glass jacket is preferred, as these are better able to maintain sufficient temperature to keep light output up, and are to some extent more robust.

CFLs used outdoors in very cold weather will light at reduced brightness and be slow to warm up. Some CFLs are better suited to outdoor use than others. Find one specified for outdoor use, or try a few and use the ones that work well in cold weather.

Outdoor Wiring

SWA (steel wire armoured) or Hi-Tuff cable should be used in preference to MICC (Mineral Insulated Copper Clad), as MICC is hygroscopic.

Outdoor wiring should be on its own RCBO (or RCD), since the failure rate of outdoor wiring is much higher than indoor wiring. If both were on the same RCD, RCBO, MCB or fuse, failure of the outdoor wiring would also cause failure of the indoor circuit to which it was connected.

Making Outdoor Lighting Look Good

2 or 3x 40w & 60w lights tend to look much better than one 100 or 150 watter. Lights among foliage look much nicer than bare lights. These 2 simple tips make the difference between bare & functional and pretty lighting.

Outdoor Light Fitting Corrosion

When picking outdoor lights, beware of cast aluminium lights with steel cover fixing screws, as the cover screws are likely to corrode solid. If cast ali fittings are wanted, use another way to secure the lids on if you want them to last. Wire ties or plastic screws are usually workable options.

Checking Competence

Is your electrician competent? Many are, but there are certainly some that aren't. If you wish you can ask them a question or 2 and check the answers. This also has the benefit of politely letting any cowboys know you might check on their work, which will be offputting to some. An example question might be: What earthing system will I get?

Low Voltage Wiring

There are several reasons to incorporate low voltage wires when rewiring. Increasing use of internet and computer networking, electronic security, more efficient and comfortable separately zoned heating control, the convenience of phone sockets in any room you want them, hifi distribution, all these can be accomodated by incorporating LV wiring into the house. Cat 5e is currently the best option for computer connectivity. No doubt this will change in future, but 5e is the standard expected to remain in use the longest, mainly due to its widespread use. Either multicore burglar alarm cable or cat5e can also be used for security, phone, door bell, intercom, Lv heating control, baby monitoring, backup lighting, fire detector interconnection, and who knows what other apps will become popular in future.

A 100m reel of multicore LV cable is very cheap at around £10, so some are now incorporating this wiring when they rewire. The labour required is not so cheap.

Night Lighting

Built in nightlighting reduces night time accidents and avoids night time dazzle. Low power low voltage cable can supply LEDs in each room, though there are other ways to do it too. This is not one of the cheapest options to have installed. Using mains 3w CFLs is a reasonable alternative.

Fear of the Dark

For small children, a 3w CFL bathroom light left on can make life easier for them. This can be fitted either as a separate fitting, or a bathroom globe type light taking 2 bulbs can be used with a twin wall switch. This is a lot less unpleasant for grownups in the night as well. Run cost if left on 24/7 is about £2.50 per year.

Flush or surface mount

Electrical accessories are usually recessed into the wall so they sit nearly flush. This looks better and avoids them being a problem with placement of furniture.

Surface mounted wiring and accessories are a cheaper option, but in most cases wont look particularly good.

This one is simple, but if you didn't know what you wanted you could end up with the cheap option.

Bare Stone walls

Exposed stone walls are difficult to wire in a way that looks good.

  • Copper MICC can be run low on the wall and left to oxidise and turn a dull colour. This is the best of the straightforward options.
  • PVC cable can be painted to stand out less. Someone with basic art skills could even camouflage it.
  • Burying the wiring in the mortar between 2 layers of stone can sometimes be an option. This will often mean using a metal sheathed wire, which will take work to shoehorn into an uneven line.
  • Low voltage light fittings can be fed from 2 cores of enamelled copper wire, which is by far the least visible of all wire types. This can be surface mounted without it being noticeable. It can also be buried under the surface or run in cracks and gaps. 12v CFLs, filament lamps and halogens are all available. To use mains light fittings at low voltage you would need to replace the bulbholders in them.
  • Flush floor mounted sockets can sometimes be used to eliminate wiring on the wall.
  • Wiring can be run in modified wooden skirting board incorporating sheet steel between wood and cable.
  • If you're brave you can make a feature out of wiring. This is difficult to make work aesthetically, but it has been achieved at times. Halogen spots clipped onto 2 thick steel cables is a now classic example of this.

Get it in writing

Unless you just want 'whatever,' you should get any features you specifically want in writing. Otherwise you may find what you get is not what you agreed on or paid for.

See Also

Bad Ideas - Lighting

Bad Ideas - Electrical

Fluorescent Lighting


Dimmed PIR Light

Halogen Lighting

Old Wiring

Discharge Lighting


You and only you are responsible for your actions. There's no point blaming me or us later if you did something not addressed by this, or misunderstood and mis-implemented, acted on an error or omission, or followed this advice and got unsatisfactory results. This writing is not intended to replace the advice of a skilled electrician that has seen your house and discussed your specific requirements, and can only be general and limited in nature. It will however enable many people to get significantly better installations and avoid some common causes of accidents and unnecessary trouble & expense.

NT 2006