Electrical Installation

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Revision as of 23:47, 25 September 2008 by John Rumm (talk | contribs) (More words added, and lots of piccies)

This article is all about the non engineering side of electrical installations. Its purpose is to explain some of the techniques that are used to when installing electrical equipment and wiring in typical domestic situations.

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Cables can be run in a large number of places and ways. However some places are better than others, and certain rules need to be followed to comply with the wiring regulations in some cases. In addition to the practical issues of cable routing, one also needs to think about what materials you are placing the cable in/under etc. since these may have effects that you need to take into account in the electrical design. E.g. a cable buried in an insulating material will not be able to lose heat as quickly as normal, and this means that the maximum current it is allowed to carry is reduced.

Wall chasing

Burying a cable in a wall is a traditional way to hide and protect the cable. Modern cables can be buried directly in plaster, or protected with capping before plastering. Before a cable can be buried however, a chase needs to be cut!

See the wall chaser article for more detail on the options for cutting cable chases in plaster and masonry.

Getting past coving and skirtings

It is all well and good chasing a wall with your trusty SDS drill or wall chaser, but what happens when you reach some architectural feature that you don't want to go hacking through, like a deep skirting board or ornate plaster cornice or moulding?

  • Long drill bit: A very long drill bit (we are talking a minimum of 400mm here to get behind small items like picture or dado rails, or more realistically a stonking great 1m long bit bit for skirtings and coving!) can be a handy way to continue a chase behind the feature you are trying to avoid. Ideally one would need to drill straight up or down through the plaster to achieve this. This is usually impossible since you can't get the drill in the right place, or at the right angle since the wall is in the way. With small obstructions (dado etc) this may not matter, drilling down behind it at a slight angle will still be ok. For a longer vertical chase, the longer bit will be required. The trick here is to apply some sideways force to the bit as you drill. It should be possible to bend the drill such that its tip *is* parallel to the wall, while keeping the drill body and you hands at the slight angle required due to the obstruction of the wall.
  • Cranked gouging chisel: specially made SDS gouges can also work well for getting behind smaller items.
  • Using the other side of the wall: As simple as it sounds, in some cases the solution to avoiding difficult chases, might be to simply use the other side of the wall. This can be ideal for a cable chase on a tiled wall in a bathroom. It can also often save time where adjacent rooms have light switches "back to back" on the dividing wall - only one chase is required for the pair. Note One will need to take care that cable routes are within the prescribed zones expected - even if this means installing an extra accessory to mark the position.
  • A long threaded bar and a lump hammer. A long SDS bit may still damage very deep coving as it is not always possible to get the drill into a vertical position. A slightly bent threaded bar can be knocked up behind deep coving and not damage it

Under floors

Cables are also often taken under suspended floors or even sometimes placed into chases cut into concrete ones.

Lifting floors

Techniques for lifting floors
Type of floor Methods
Traditional floorboards A traditional boarded floor is one of the easier ones to get under! The traditional approach simply uses a pry bar and or bolster chisels to leaver it up. Sometimes you also need to cut a board. There are a number of approaches to this:
  • floorboard saw (one with a curved toothed section) will allow a plunge cut to be made over a joist.
  • Japanese style azebeki saws are even better.
  • Bend 'n' saw - sometimes if the boards have enough bend in them, you can leaver one up in the middle of a section, and slide a chisel under it propped up on the adjacent boards. This will then let you at it with a traditional panel or tenon saw.
  • If you know the thickness of the boards, then you can snap off a jigsaw blade such that when the jigsaw is at the lowest part of its stroke, the blade is the same depth (or fractionally deeper) than the boards. If needs be a hold can be drilled to allow the blade some entry room.
  • If you are in a hurry, a plunge cut with a circular saw - again with the depth set to no deeper than the board depth.
  • Oscillating multi-tools like the Fien Multimaster and the similar concept Bosch PMF 180, really come into their own here since they allow perfect neat plunge cuts into boards. The very narrow kerf of the blade also leaves far less visible damage once the floor is put back down again.
Tongue and groove floor boards Similar to the above, except you will also have to rip cut through (or split off) the tongue on the board first, in order to be able to lift it.
Chipboard sheet Generally far harder to work with since the boards are not only tongue and grooved at the edges, they are also large (typically 8' x 2'). In many modern houses, its also not uncommon for the partition walls to be built over the floor panels or at least the skirtings etc to be fixed over them. This can make removal of a whole board impossible. The best way to deal this this floor is to cut an access panel:
  • The Trend Routabout jig is designed for this purpose, and makes it easy to not only get access, but also fix the hole afterwards.
  • The jigsaw, oscillating tool, and circular saw options described above also work. You will need to use screws and battens under the cut edges however to restore the strength of the floor afterwards (chipboard is string in gig sheets, but small strips are quite weak without support on all sides).
Laminate While not easy it is possible to remove a plank of laminate in a floor. For the click together type, it may be simplest to start un-clicking panels at the edge of the room, and work your way back to where you need your access point. For glued panels, you will need to cut out a board. The way to do this is with a circular saw (preferably a small one - cordless ones are ideal). Set the cut depth to laminate thickness, and cut through the board all round close to its perimeter. Once the main bit is removed, use a chisel to break away the remaining edges from the adjacent boards.

To replace the board you will need to cut away the underside section of the groove edges of the new plank, and then glue and lower the new board into place. Depending on how cleanly you were able to remove the tongue from the goove of the adjacent board, you may also need to cut this off the new board.

Entry via a ceiling

The lateral thinkers way to get under a "difficult" upstairs floor is via the ceiling of the room below. In many cases some new plasterboard and a bit of patching is a much quicker solution that lifting an engineered wood floor and underlay, or clearing a particularly cluttered room.

Over Ceilings

In some cases the same as under a floor! However this also includes over false ceilings (which if you have lots of wires to hide or lots of ceiling piercing lights to install, may be well worth building for the purpose). It also includes through loft spaces. Once caution to watch is to keep modern PVC cable away from polystyrene insulation (the plasticiser leaches out of the PVC into the polystyrene, leaving a gooey mess, and rather brittle cable insulation)

In hollow walls

It is also sometimes possible to drop a wire down a hollow stud wall (either plasterboard or lath and plaster). Note it is not recommended to place wires in the cavity of exterior walls, where they could cause dampness bridging, and be adversely affected by cavity wall insulation injected at a later stage.

Getting wires into a stud wall in the first place is easy to do when building it. However at a later date it is not as easy and you may meet a few obstacles:

Getting round problem walls
Problem Solutions
Catching a wire Feeding a wire along the inside of a wall is one thing, but getting the free end out again without making a hand sized hole in the wall is another problem! Techniques to try include:
  • Standard retractable tape measure. Push a loop of this into the wall through a hole. If you keep feeding in tape, then inside the wall it will expand out against the sides etc. This makes a larger target to feed the wire through. Pulling the loop of tape back through the hole can then "snare" the cable.
  • The same trick also works (better) with a length of flexible plastic coated net curtain wire used as the loop.
  • A length of chain, can also make a good weight to pull a draw string through. It has the advantage of being easy to "catch" with a magnet or magnetic pick up tool.
Getting past studs and noggings It is rather hard to drill a hole through the side of a lump of wood if all you can see is a board covering its front face! However there are ways:
  • Long drill bit. If you have a hole to work from (say a cutout for a socket box) then a long drill bit at an shallow angle can be used to get through at least one obstruction. Spade bits with an extension shaft or two can be very useful here since they let you make a big diameter hole at some distance.
  • Notching from the face. You can cut a notch in the face of a stud or nogging without causing too much damage to the face of the wall, by drilling a series of overlapping holes with a wide spade or auger bit.

Pull wires / cords / tapes

Ideal for getting wires through tortuous paths. There are specialist tapes and cords for the purpose, but almost any bit of string or even and old cable may be used. Fishing line is often very good in that it is strong, long, thin, slippery, and cheap! The real art with any pull string is how you get it into location in the first place! Some of the more imaginative options include:

  • Add a weight or ball to the end and throw, catapult, or otherwise propel it in the desired direction. A metal weight like a small bit of chain can make retrieving the end easy with a magnet on a stick.
  • Radio controlled cars and other self propelled toys, can be "driven" to the destination while towing a wire - handy for ground floor voids that are not big enough (or too full of rat crap) to make climbing under yourself desirable.
  • Small children can often be pressed into service with some bribery ;-)
  • Cat, cable tie, and a sardine might also work!

There is a whole subset of these, for getting a pull cord through ducts and pipes. Most involve either a vacuum cleaner to suck something through the ducts, or a compressor to blow something through it. Rags, plastic bags, and tennis balls being tried and tested candidates.

Also when pulling pull cords, you may need to allow for the possibility that all you will pull with the first cord is a stronger cord! Working your way up to the particularly heavy or stiff cable that ultimately needs to get through.

One handy tip when laying in wires in many cases, is to pull a new cord through with each wire. That way you can always add more later.


Sometimes some extra assistance is needed when getting wires and cables through tight spaces and into pipes, ducts, conduits etc. There are specialist cable pulling lubricants available like "Yellow 77" that are designed for this purpose and won't hurt or react with the cable in any way. However other substances are often used:

  • Talc
  • Grease (silicone is better - won't attack the plastic)
  • PTFE sprays
  • WD40 (not much good - but sometimes better than nothing)
  • Soap / washing up liquid

Push rods and sticks

Very useful for getting wires through awkward spaces. The simplest (and a widely used) stand in for "real" ones, are simply lengths of plastic conduit or trunking (and especially the lid off a bit of mini trunking!). The posher versions look rather like a narrow gauge version of a set of drain rods. Often made from fibreglass, they can be screwed together to make a very long stick (10m is not uncommon) and the end of the stick can be equipped with hooks and loops and other gizmos to make getting them round corners easier.

One word or warning with the fibreglass sticks, wear gloves when handling them - otherwise you can get a nasty glass splinter!


The following is a big list of tools, some are essential, and some just handy to have. Essential in this case means these are tools that you need to do the job safely - you may be able to do it will less, but you may be putting yourself at risk when doing so.

Many of the mechanical aspects of wiring have little to do with the things that one traditionally associates with the work of an electrician, and are really nothing more than general building and carpentry tasks.

Type Description Need
SDS Drill (3 function) The ability to not only drill holes, but also quickly and neatly chisel out holes for socket boxes, and neat wall chases make the SDS drill a wonderful time saver. Very Handy
Cordless drill / driver In general cordless tools are very handy to have for electrical work since you will often be working in areas without power. Making holes, and fixing things in place probably come right near the top of list of tasks faced by anyone undertaking electrical work. A medium size (say 14.4V or better) combi drill is ideal for this sort of work. Having the hammer facility can make drilling holes into masonry for wall plugs far simpler. Very Handy
Insulated screwdrivers (VDE)


VDE tools[1] are insulated and tested to to a high standard. This ensures that should the metal part of the tool make contact with live metalwork, no harm will come to the person holding the other end. These are absolutely essential when working on electrical installations. Not just for the rare occasions where live working is required, but the far more typical cases where one is working in close proximity to live circuits, or even on circuits that really ought to be dead, but are not!

All things said and done, you can make do some ordinary screwdrivers for jobs not involving work on electrical fittings etc, and you may choose to buy a limited set of VDE insulated drivers: a medium phillips (typical for MCB terminals) and a small and medium flat blade for other terminals.

Side Cutters


VDE insulated side cutters are essential (one day, you *will* pick the wrong cable to cut). Side cutters are used for cutting cables and wire to length, and they are also often invaluable for stripping cables of their outer insulation. Some cutters also include specific facilities for wire stripping, [eg]. Essential
Wire Strippers


Good wire strippers make life very much simpler (while it is true that someone proficient with side cutters can often strip a wire quite satisfactorily with them as well, there is far more scope for bruised knuckles, damaged conductors, and tatty looking wire ends without them). The style of wire cutter is much a matter of personal preference. Side strippers are quick and easy to use - especially one smaller wires. The end action ones may be better for tough insulation found on the thicker and also special purpose wires. Some people also like to have an automatic wire stripper. These can make repeated stripping operations very much quicker. Highly desirable
Combination pliers


regular square nosed medium set are useful for holding, bending, and twisting wires, tightening locknuts etc. In fact anywhere you need extra gripping power. Handy
Long nose pliers


A good pair of long nose pliers are the ideal tool for fishing wires out of awkward corners, and holding tricky wires in place as you tighten terminal screws. Note however that even with VDE insulated ones, care must be taken, since they have a large expanse of exposed metalwork that could easily short against live parts or earthed casework. Very Handy
Ratchet action cable crimper


Essential for making sound wire joints which will later become inaccessible, or where space is too restrictive to allow terminal (aka "choccie blocks") to be used. See the Cable crimping article for full details of how to use these. Often Essential

[1] Just in case you were wondering what VDE stands for, the answer is: It wouldn't help much as the words are German! It is an internationally accredited German testing and standards institute. In their own words:

"The VDE Testing and Certification Institute is accredited on a national and international level for the area of testing and certification of electrotechnical equipment, components and systems. Testing of electrotechnical products is conducted for safety, electromagnetic compatibility and other characteristics."

Test gear

Type Description Need


A simple multimeter will be very handy for all sorts of tests, ranging from a simple "Is this wire live?" test, to checking continuity, and measuring cable resistances.

(The clamp meter shown, also has the capability to measure the current flowing in a single wire (i.e. not a cable containing live and neutral, but either live or neutral in isolation) without needing to make any electrical connection to a circuit. Clamping this round the meter tails for example will let you read the total current draw on an installation with no risk)

Test lead extension


Very handy for working out which socket is connected to which and various other tests that require you to measure continuity between more distant points. A workable alternative can be knocked up from any bit of cable or flex, but the proper lead is so much easier to use. Handy
Volt stick A simple non contact indicator that detects the presence of mains voltage on a wire. These are very good testing that a wire is safe to cut etc, when working on partially isolated systems.

(Note for safety, it is always wise to test the volt stick on a known live circuit both before and after testing the wire you want to know the status of. This protects you from a freak accident should the detector fail at an in opportune moment!)

Very Handy
Socket Tester


A simple plug in tester that will indicate a wide range of potential faults with sockets and their wiring. Very quick and easy to use, and unlike probing about in the back of a socket with your multimeter, or trying to find a suitable appliance to plug into a socket to test it, much safer! Very Handy

Advanced test gear

For anything other than basic alterations and additions to existing circuits, some more sophisticated test equipment is really required. These items can be bought as separate units or as an integrated tester that combines all the functions. Again, you will probably live if you don't use this kit, but it is the only way you are actually going to prove that your wiring is performing as it should)

Type Description
Insulation resistance tester ("megger")


These are often multi function devices that measure wire resistances with good accuracy, and are also able to perform resistance measurements using a very high test voltage (e.g. 500V or more). This will detect any part of a circuit (or whole installation) that has failing or damaged insulation. These can be very handy for finding tricky faults causing nuisance tripping of RCDs for example.

Great care must be taken with these devices. Firstly they will give you a shock if you hold the probes and push the test button. Secondly, you need to make sure there is nothing connected to the circuit under test that might be damaged by the high test voltage (some RCDs, Dimmers, and electronic power supplies etc)

Earth loop impedance tester


These are very useful devices that will allow you to measure the earth fault loop impedance at any socket in a circuit. This lets you prove the effectiveness of the earth, and establish data you will need for circuit design. They can also be used to measure the performance of earth rods. In many cases they will also let you measure the Prospective Short Circuit current and the Prospective Fault Current of a circuit.

Older devices like the one pictured, perform tests using a fairly substantial test current. This is good in the sense that it proves that the earth really does work under simulated "fault" conditions, but has the downside of tripping any RCD protecting the circuit under test. More modern devices also have the capability of carrying out non tripping tests.

RCD Tester


About the only realistic way to properly test a RCD. These inject a user selectable earth leakage into a circuit, and then time how long (in 1/1000ths of seconds) it takes the RCD to disconnect the power. More sophisticated versions can also carry out "ramp" tests that slowly increase the leakage until the trip point is found.

Not only required for RCD tests, they can often help establish the cause of nuisance trips.

Good workmanship

Mechanical protection

Type Description
Capping to protect cables from damage by plastering trowels, capping is ideal (plastic or metal). The advantage of capping over conduit is that it is easy to fit after a cable has been installed, and it won't affect the cables ability to lose heat.
Plastic Conduit Plastic conduit can be used for added protection to surface run cables. Note it is not well suited to burial since it offers little protection from drills, nails and screws, while lowering the current carrying capacity of the cable.
Metal conduit Metal conduit can be buried, and also (if installed correctly) can be used as the circuit protective conductor (i.e. "earth"). It also offers good protection against penetration. It can also be surface run and offers good protection in harsh service conditions. Metal conduit is not however easy to use, since it requires additional tooling to bend, cut and thread the sections.
Grommets Rubber grommets should be used anywhere a cable passes through a hole in a metal enclosure or back box. These will stop the insulation being damaged by sharp edges. (not only from movement of the cable during installation, but also from movement caused by vibration or thermal expansion effects in use).
Strain relief sleeves Sleeving can help protect flexes and cables at any point they will be subject to stress caused by carrying their own weight from a suspension point.
Glands When attempting to make a cable entry or exit waterproof, or when working with cables that must be terminated with glands like SWA, glands must be used. These not only fix the cable in place but also offer the water protection required, strain relief and often a facility to connect the cable screen (where present) to earth.
Minimum bend radii Care must be taken with cables, to not attempt to bend them too acutely, since this may cause damage.


  • Clips
  • Trunking

Making good

Once you have installed and tested all your new wiring, there is the rather more mundane task of filling all the wholes, and reinstating the fabric of the building before you lose too many household pets or children into floor voids or incur the wrath of the style police!

Filling chases

Replacing floor boards

See also