From the electricity meter, the current passes to a consumer unit with an integral mains switch, or, in older installations, to a fuse board with separate switches and fuse boxes. The power is then transferred to the wiring circuits either by means of individual fuses or by circuit breakers. Either type of device serves an essential safety function. If a fault or an overload results in more current flowing through a circuit than it is designed to carry, the fuse will melt or the circuit breaker will open, thereby cutting off the circuit from the mains supply.
In this way, the excess current is prevented from generating the kind of heat that usually causes a fire. Miniature circuit breakers (M.C.B.s) are more convenient than fuses, which have to be repaired or replaced after a circuit interruption. Once the cause of the interruption has been corrected, a circuit breaker is simply reset by pushing the switch or button to the “on” position. M.C.B.s are a fairly recent development, however, and most electrical installations are still protected by fuses. These are of two types—rewirable and cartridge—and they are housed i n porcelain or plastic fuse holders which plug into the fuseways of the consumer unit or fuse box. Plastic holders are usually colour coded according to their current rating: 5 amp is coloured white, 15 amp blue, 20 amp yellow, 30 amp red and 45 amp green. The most widely used of the two fuses is the rewirable type, in which the fuse element – a piece of thin wire—is held in position by a screw terminal on either side of the holder.
If a fuse blows, melting the wire between the terminals, first the remnants of the old wire are removed and then a new piece of the same current rating is fitted in its place. In the case of the cartridge fuse, the element is enclosed in a small, metalcapped tube which slots into two spring contacts on the holder. The disadvantage of a cartridge fuse is that it cannot be repaired; once it has blown, it has to be replaced . It is also more expensive to replace than the rewirable type.
On the other hand, cartridge fuses come in different sizes according to their current rating, so that it is impossible to fit, say, a 20 amp fuse into a 5 amp holder. Like plastic fuse holders, cartridge fuses are colour coded so that they can be easily identified. The most important advantage of all is that a cartridge fuse provides greater protection for the circuit than a rewirable fuse. This is because i t takes less excess current to blow the cartridge fuse. For example, i t would need only 45 amps to blow a 30 amp cartridge fuse compared to about 60 amps for a 30 amp rewirable fuse.
In addition to protecting the circuits in your home, fuses and M.C.B.s perform another and all-important safety function. Because fuses can be removed and M.C.B.s switched off, they enable you to ” kill” a circuit so that you can work on it without the risk of receiving a shock.
Old electric meters includes a small disc which revolves a certain number of times for every kWh (kilowatt-hour) or unit of electricity consumed. The disc operates, in turn, numbered indicators to register the amount of current used. Some meters have digital dials that resemble the milometer of a car, and they are read in the same way. More common, however, is the clock-type meter with five separate dials, each of which supplies one digit for the reading.
The lower dial, which is red, shows fractions of a unit and is used only for test purposes. The left-hand dial registers tens of thousands, the next thousands, and so on to the right-hand dial, which registers single units. The numbers on the dials are arranged alternately clockwise and anticlockwise, and the pointers on the dials move accordingly.
When taking a reading, start with the left-hand dial and work across to the right of the meter. If a pointer is between two numbers, always take the lower number. If a pointer is directly over a number, the clue to a correct reading is provided by looking at the adjoining dial, as explained in the example on the right. To check your electricity bills, as you should periodically, make two consecutive readings and subtract the first from the second to calculate the consumption for the intervening period.
Take each reading on the day the official from the Electricity Board calls to make his own reading. Then compare your results with the figures on the second bill.
How can you check if your meter is working accurately?
The simplest way is by making use of the red dial, which measures 0.1 (or 1/10) of a unit. First, switch off a l l electrical equipment in the house and make sure that the rotating disc is stationary. Note the position of the pointer on the red dial and then switch on a load of 1 kW—for instance, of a 1 kW electric fire. If the meter is working accurately, the pointer should make one revolution—equivalent to one whole unit – in an hour.
Electricity generated in the power station comes into your home at 240 volts and is transmitted by a service cable which terminates in a sealed unit containing the Electricity Board’s service fuse. This is generally rated at 100 amps, but 60 or 80 amps is possible in older houses. This fuse provides a last defence in the unlikely event that your own fuses or M.C.B.s (miniature circuit breakers) fail to operate.
From the sealed fuse unit, the current passes through a meter, which records the amount used, and flows on through a consumer unit. This incorporates the fuses or M.C.B.s for all the house circuits. The cables of these circuits convey the current from the consumer unit (or, in older installations, the fuse board) to lights, switches and socket outlets. Each circuit has a specific current rating determined by the maximum load it is expected to carry. There are four standard current ratings—5 amps for lighting, and 15, 20 and 30 amps for power. A fifth rating—45 amps—has recently been introduced for “electricaire” central heating units and large electric cookers. Each of the two principal types of circuit— lighting and power—may be based on one or other of two wiring systems.
• RING FINAL CIRCUIT WIRING. In houses wired since 1947, most or all of the power is supplied by a ring final circuit— so called because the circuit is wired in the form of a continuous ring starting and ending at a single 30 amp fuse or M.C.B. in the consumer unit.
A ring final circuit can supply any number of 13 amp socket outlets and fixed appliances, provided only that the total floor area covered by the circuit does not exceed 100 square metres. In addition, branch cables called spurs may be run from the ring cable to supply socket outlets in remote positions—for example, a loft or basement. The number of spurs must not exceed the number of socket outlets and fixed appliances connected directly to the ring, and each spur may only supply one single or one double outlet. A spur is connected to the ring cable at the terminals of a ring socket outlet or at a 30 amp joint box inserted into the ring.
RADIAL WIRING. As with a ring final circuit, the function of a radial power circuit is to supply power for a number of 13 amp socket outlets and fixed appliances. However, whereas a ring final circuit terminates back at the consumer unit, a radial circuit terminates at the last outlet. Furthermore, the maximum floor area that may be covered by a radial circuit is much less than that for a ring final circuit. A radial circuit of 20 amp current rating may supply an unlimited number of outlets and appliances within an area of 20 square metres, and one of 30 amp rating may supply an unlimited number within an area of 50 square metres.
Generally, radial circuits are best used to supplement ring final circuits, particularly in a kitchen with a large range of electrical appliances. However, an appliance with a load in excess of 3,000 watts (3kW) should be wired on its own individual circuit protected at the consumer unit by a 30 or 45 amp fuse or M.C.B. In fact, all power circuits installed before 1947 were wired to just one socket outlet or fixed appliance apiece. The outlets were designed to take round-pin plugs of 2, 5 or 15 amps—the then standard current ratings— and the plugs did not contain their own fuses. If you have round-pin outlets and the circuits run from a number of separate fuse boxes, each with its own mains switch, then you can be fairly certain that the wiring is more than 55 years old. In that case, you should have the wiring checked as soon as possible, since it will certainly have deteriorated and may even be dangerous. Indeed, the electricity boards have declared that “any house over 25 years old may have dangerous wiring”.
• JOINT-BOX WIRING. In many houses built before 1966, the lighting circuit runs from a 5 amp fuse in the consumer unit to a series of joint boxes fixed between ceiling ioists. From each box run two more ;ables—one to the corresponding switch, the other to the ceiling rose.
• LOOP-IN WIRING. A modern lighting installation is most likely to use the loop-in system—so called because the supply cable runs direct from one ceiling rose to another Until all the roses are linked, or looped in, together. One cable is run from each ceiling rose to its corresponding switch.
A more Modern wiring. In a house with ring final circuit wiring, all the circuits run from a consumer unit with a single mains switch. Socket outlets are designed to take square-pin plugs of 13 amps and are connected by a continuous ring of cable. In most cases, one ring serves the upstairs socket outlets, and a second supplies those on the ground floor. In the same way, each floor is usually served by its own lighting circuit running direct from one ceiling rose to another. A cable goes from each ceiling rose to its corresponding light switch.
Very old wiring
In a house with pre-1947 radial wiring, the circuits run from a number of separate fuse boxes, each with its own mains switch. All the power circuits are connected to one socket outlet or one fixed appliance apiece, and the socket outlets are designed to take round-pin plugs of 2, 5 or 15 amps. The lighting circuits— usually one for each floor—run to joint boxes fixed between the ceiling joists. From each joint box one cable goes to the corresponding light switch and another goes to the ceiling rose.
Tools for the electrical repair and improvement jobs require only a modest investment. Some of them may already be in your home tool kit -for example, such general-purpose devices as an electric drill, screwdrivers, saws, a hammer and a chisel. Others are more specialized and may need to be added.
• TORCH. Always keep a torch by the fuse board or consumer unit. Then, if a fuse on a light circuit blows during the night, you will not have to grope about in the dark to repair or replace it.
• PLIERS. Two kinds are needed for electrical work. Long-nose pliers have elongated jaws that are ideal for bending a loop in the end of light-gauge wire so that it can be attached to a terminal. The jaws should be serrated to provide a firm grip and there should be cutting edges near the pivot so that you can snip the wire. Electrician’s pliers are used for bending and shaping heavy-gauge wiring and for twisting out removable parts from certain electrical components. These pliers should also have cutting edges and serrated jaws.
• DIAGONAL CUTTERS. Although electrician’s pliers can be used to cut cable, a pair of diagonal cutters will make the job much easier.
• WIRE STRIPPERS. As the name suggests wire strippers remove the insulation from electrical wiring. In the type shown below, there is a notched cutting edge at the end of each arm and a screw for adjusting the arms to the thickness of the wire. The cutting edges sever the insulation enclosing the wire but stop short of the wire itself, allowing the insulation to be pulled away.
• KNIFE. A sharp knife is needed to slit and then trim back the tough PVC sheathing round cable. A utility knife with a retractable blade is suitable.
• TERMINAL SCREWDRIVER. You need a variety of screwdrivers for wiring jobs, but the one you will use most frequently is the terminal type with parallel-sided tip. Although each of the tools shown below is properly insulated, views differ about the value of insulation. On the one hand, it is regarded as unnecessary since work should never be carried out on live circuits. On the other hand, insulation is regarded as a wise safety precaution in the event of mistakes.
A short video explaining the electrical requirements for an electric shower, in particular what to check before buying to ensure your intended purchase is compatible with your mains electric supply.
Instantaneous Electric Showers are still one of the most popular types of shower sold in the UK today. Which is why Triton manufactures an extensive range to suit all tastes and budgets.
An electric shower simply connects to a cold water supply and your mains electric, so it’s versatile enough to suit any home no matter what your plumbing system.
They are easy to install and they give you and your family instant hot water – any time, day or night.
So, what are the electrical requirements you need to know before you can choose an electric shower?
First of, all electric showers need to connect to your mains electric supply.
More to the point, it must have its own dedicated supply from your consumer unit.
It must not be connected to a ring main, spur, socket outlet, lighting circuit or cooker circuit.
The important thing is to ensure that the electric supply is adequate for the shower and existing circuits.
Check that your consumer unit has a main switch rating of 80A or above and that it has a spare fuse way to take the fuse or Miniature Circuit Breaker (MCB) for the shower.
The correct rating of MCB or fuse will depend on the kilowatt rating of the shower that is to be fitted. For more information on kW ratings take a look at our “What is a kW rating?” video.
If your consumer unit has a rating below 80A, or if there is no spare fuse way, then the installation will not be straightforward.
It may require a new consumer unit serving the house or just the shower.
For your protection, a 30mA residual current device must be installed. This may be part of the consumer unit or a separate unit.
The size of electric cable you need from the consumer unit to the shower depends on a number of things, such as – the kilowatt rating of the shower and the method of installing the cable…
…i.e. is it, or will it, be surrounded by loft or wall insulation. As a result, the cable could be anything from 6mm, to 10mm, or even 16mm.
To obtain full advantage of the shower, use the shortest cable route possible from the consumer unit to the shower.
In any event, it is essential that individual site conditions are assessed by a competent electrician in order to determine the correct cable size and permissible circuit length.
Finally before your electrics can go into the shower unit, you need to install a 45 amp double-pole isolating switch into the circuit.
This can either be installed inside or outside of the bathroom, but it must be readily accessible to switch off after using the shower.
Once you’ve fitted the switch into the circuit, all you have to do is complete the cable to the shower.
Depending on the model of shower, the cable will enter through either the top, bottom, sides or back of the unit.
Simply connect into the terminal block making sure the connections are good and tight so there is no risk of the cable overheating.
The final thing to say is that all electric showers must be installed in accordance with all the relevant water supply, electrical and building regulations.
Electric Showers: Plumbing Requirements.
A short video explaining the plumbing requirements for an electric shower, in particular what to check before buying to ensure your intended purchase is compatible with your cold mains water supply. The video also offers suggestions should your cold mains water supply not be adequate.
Instantaneous Electric Showers are still one of the most popular types of shower sold in the UK today. Which is why Triton manufactures an extensive range to suit all tastes and budgets.
An electric shower simply connects to a cold water supply and your mains electric, so it’s versatile enough to suit any home no matter what your plumbing system.
They are easy to install and they give you and your family instant hot water – any time, day or night.
So, what are the plumbing requirements you need to know before you can choose an electric shower?
First of all, you need to check that your mains water pressure and the flow to the shower meets the minimum required.
Water pressure is measured in units known as “bars”. 1 bar is approximately equal to a column of water 10m high.
The water pressure required for an electric shower varies from one electric shower to another depending on the manufacturer. Some require half a bar, while others require one bar or above.
The minimum flow rate required to operate the shower efficiently also varies from one unit to another and can be up to 10 litres per minute.
The kW rating of the shower also affects the water pressure and flow rates required. For more information on kW ratings take a look at our “What is a kW rating” video.
For guidance on water pressures and flow rates contact your local water company or consult a competent plumber.
If the water supply is adequate, you simply need to take a connection from a rising cold mains supply and run a pipe to your shower. Fit an isolating valve into the pipe before the shower for future servicing.
Depending on the model of shower, the pipe will enter through either the top, bottom, sides or back of the unit.
Simply connect the incoming water supply to the inlet of the shower making sure the connections are good and tight so there is no risk of leaking.
If the required water pressure and flow rate is not available from your mains water supply then it it’s unlikely that the shower will work.
However, this doesn’t stop you getting the shower you want.
You can always fit a separate pump in the water supply before the shower.
In this case, the shower cannot be connected to the cold mains supply, but to a cold water tank, instead.
Alternatively, you can choose an electric shower with a built-in pump such as Triton’s T90xr which also connects to your cold water tank.
For more information on this take a look at our “What is a pumped electric shower?” video.
The final thing to say is that all electric showers must be installed in accordance with all the relevant water supply, electrical and building regulations.
The hardest part of the average electrical job is running the cables: it takes up a lot of time and a lot of effort. But there are certain techniques used by professional electricians which can make it much easier.
Before you get involved in the details of how to install the wiring, there are few questions you must answer. Does it matter if the cable runs show? Is it safe ? Does it comply with the Electrical Regulations? This is because there are only two approaches to the job of running cable. Either you fix the cable to the surface of the wall, or you conceal it. The first option is far quicker and easier but doesn’t look particularly attractive; it’s good enough for use. in, say, an understairs cupboard. For a neater finish, using this method, you can smarten up the cable runs by boxing them in with some trunking. Many people, however, prefer to conceal the wiring completely by taking it under the floor, over the ceiling, or in walls.
Planning the route
With concealed wiring, the position is more complicated. When running cable under a floor or above a ceiling, you must allow for the direction in which the joists run – normally at right angles to the floorboards – and use an indirect route, taking it parallel to the joists and/or at right angles to them. When running cable within a wall, the cable should always run vertically or horizontally from whatever it supplies, never diagonally.
Concealing cables in walls
There are two ways to conceal cable in a wall. With a solid wall, chop a channel (called a ‘chase’) out of the plaster using a club hammer and bolster chisel, carefully continuing this behind any skirting boards, picture rails, and coverings.However, to give the cable some protection, it is better to fit a length of PVC conduit into the chase and run the cable through this before replastering.
To continue the run either above the ceiling or through the floor before you position the conduit, use a long drill bit so you can drill through the floor behind the skirting board. If a joist blocks the hole, angle the drill sufficiently to avoid it. With a hollow internal partition wall, the job is rather easier, because you can run the cable within the cavity. First drill a hole in the wall where the cable is to emerge, making sure you go right through into the cavity. Your next step is to gain access to the timber ‘plate’ at the very top of the wail, either by going up into the loft, or by lifting floorboards in the room above.
Drill a 19mm (3/4in) hole through the plate, at a point vertically above the first hole, or as near vertically above it as possible. All that remains is to tie the cable you wish to run to a length of stout ‘draw’ wire – singlecore earth cable is often used – and then to tie the free end of this wire to a length of string. To the free end of the string, tie a small weight, and drop the weight through the hole at the top of the wall. Then all you do is make a hook in a piece of stout wire, insert it in the cavity, catch hold of the string and pull it (and in turn the draw wire and cable) through the hole in the room below.
What are the snags?
There are two. You may find that, at some point between the two holes, the cavity is blocked by a horizontal timber called a noggin. If this happens, try to reach the noggin from above with a long auger bit (you should be able to hire one) and drill through it. Failing that, chisel through the wall surface, cut a notch in the side of the noggin, pass the cable through the notch, and then make good.
The second snag is that you may not be able to reach the top plate to drill it. In which case, either give up the ideas of having concealed wiring, or try a variation on the second method used to run cable into the cavity from below the floor. Here, it is sometimes possible to lift a couple of floorboards and drill up through the plate forming the bottom of the wall. Failing that you have to take a very long drill bit, drill through the wall into the cavity, then continue drilling through into the timber plate. You can now use the weighted string trick to feed the cable in through the hole in the wall, and out under the floor.
Running cable beneath a floor
The technique for running cable beneath a suspended timber floor depends on whether the floor is on an upper storey and so has a ceiling underneath, or is on a ground floor with empty space below. If it’s a ground floor, it may be possible to crawl underneath and secure the cable to the sides of the joists with cable clips, or to pass it through 19mm (3/4in) diameter holes drilled in the joists at least 50mm (2in) below their top edge. This prevents anyone nailing into the floor and hitting the cable.
If you cannot crawl underneath, then the cable can be left loose in the void. But how do you run it without lifting the entire floor? The answer is you use another trick, called ‘fishing’. For this, you need a piece of stiff but reasonably flexible galvanised wire, say 14 standard wire gauge (swg), rather longer than the intended cable run, and a piece of thicker, more rigid wire, about 1m in length. Each piece should have one end bent to form a hook; Lift a floorboard at each end of the room and use a push and pull action to get the electrical cable in place.
Hollow internal partition wall
Drill a hole in the top or bottom plate, then drill another in the wall where the cable is to emerge. Drop a weighted piece of string through one of the holes and hook it out through the other. Use this to pull through a stout draw wire which is attached to the cable.
• if the weighted piece of string gets obstructed by a noggin or its way to the hole in the wall, use a long auger bit to drill through the noggin.
• don’t pull the cable through with the weighted string – the string tends to snap
• never run cable down the cavity of an external wall – treat these as solid walls.
Under floors
Use a technique known as fishing:
• lift the floorboards at either end of the run
• thread stiff wire beneath the floor through one hole and hook it out of the other with another piece of wire • use the longer piece of wire to pull the cable through.
• if there’s a gap beneath a ground floor you can ‘fish’ the cable diagonally across the room under the joist
• if the gap under the joists is large enough you can crawl in the space clipping the cable to the joists
• where the cable crosses the joists at right angles, run it through holes drilled 50mm (2in) below their top edges.
Over ceilings
If you can get above the ceiling into a loft, you can clip the cables to the joists. Otherwise you’ll have to ‘fish’ the cable across.
Metal boxes are recessed into the wall and provide a fixing for the socket itself. Knockouts are provided in the back, sides and ends to allow the cable to enter the box. Rubber grommets are fitted round the hole so the cable doesn’t chafe against the metal edges.
Elongated screw slots allow box to be levelled when fixed to wall. Adjustable lugs enable final adjustments to level of faceplate on wall. Boxes are usually 35mm deep, but with single-brick walls boxes 25mm deep should be used, along with accessories having deeper-than-usual faceplates.
CHECKING OUT A RING CIRCUIT These instructions assume that your installation conforms to the Wiring Regulations. If it seems to have been modified in an unauthorised way, get a qualified electrician to check it.
TURN OFF THE POWER SUPPLY.
Start by undoing a socket near where you want to install the new socket.
Adding a spur to a ring
Once you’ve established you’re dealing with a ring circuit and what sockets are on it, you’ll need to find out if any spurs have already been added. You can’t have more spurs than there are socket outlets on the ring itself. But unless the circuit has been heavily modified, it’s unlikely that this situation will arise. You’ll also need to know where any spurs are located – you don’t want to overload an existing branch by mistake. You can distinguish the sockets on the ring from those on a spur by a combination of inspecting the back of the sockets and tracing some cable runs. But remember to turn off the power first. When you’ve got this information, you can work out whether it’s feasible to add to the ring circuit. And you’ll have a good idea where the cable runs.
Installing the socket
It’s best to install the socket and lay in the cable before making the final join into the ring, since by doing this you reduce the amount of time that the power to the circuit is off. You can either set the socket flush with the wall or mount it on the surface. The latter is the less messy method, but the fitting stands proud of the wall and so is more conspicuous.
Flush-fixing a socket on a plasterboard wall is a little more involved. If you choose to surface-mount the socket, all you have to do is to fix a PVC or metal box directly to the wall after you’ve removed the knockout (and, if metal, useagrommet) where you want the cable to enter. The socket can then be screwed directly to this.
Laying in the cable
Because cable is expensive, it’s best to plan the spur so that it uses as little cable as possible. When you channel cable into a wall you’ll need to chase out a shallow run, fix the cable in position in oval PVC conduiting. It won’t give any more protection against an electric drill, but it’ll prevent any possible reaction between the plaster making good and the cable sheathing.
Always channel horizontally or vertically, and never diagonally, so it’s easier to trace the wiring run when you’ve completed decorating. You can then avoid the cable when fixing something to the wall. Normally the cable will drop down to below floor level to connect into the circuit. Rather than remove the skirting to get the cable down to chip out a groove.
You’ll then have to drill down through the end of the floorboard with a wood bit. Alternatively, you can use a long masonry bit with an electric drill to complete the task. But if the floor is solid, the ring is usually in the ceiling void above, in which case the branch will drop down from the ceiling. And this will involve a considerable amount of channelling out if you want to install the new socket near floor level. Stud partition walls also present a few problems. If the socket is near the floor, you should be able to get a long drill bit through the hole you cut for the socket to drill through the baseplate and floorboard. You can then thread the cable through. But if the socket is to be placed higher up the wall, noggings and sound insulation material may prevent the cable being drawn through the cavity. In this case you will probably have to surface-mount the cable. In fact, surface-mounting is the easiest method of running the cable.
All you do is fix special plastic conduit to the wall and lay the cable inside before clipping on the lid. But many people regard this as an ugly solution. When laying cable under ground floor floorboards you should clip it to the sides of the joists about 50mm (2in) below the surface so that it doesn’t droop on the ground.
When you have to cross joists, you’ll need to drill 16mm (5/sin) holes about 50mm (2in) below the level of the floorboards. The cable is threaded through them and so is well clear of any floorboard fixing nails. Connecting into the circuit If you use a junction box, you’ll need one with three terminals inside. You have to connect the live conductors (those with red insulation) of the circuit cable and the spur to one terminal, the neutral conductors (black insulation) to another, and the earth wires to the third.
You might decide that it’s easier to connect into the back of an existing socket rather than use a junction box, although this will probably mean some extra channelling on the wall. Space is limited at the back of a socket so it may be difficult to fit the conductors to the relevant terminals. However, this method is ideal if the new socket that you’re fitting on one wall is back-to-back with an existing fitting. By carefully drilling through the wall a length of cable can be linked from the old socket into the new.
