Why would you want to fit a doorbell in the first place? Do your visitors stand frustrated on the doorstep because they can’t make themselves heard? If so, the answer is to fit an electric doorbell. Neat and unobtrusive, they’re easy to install and will always let you know when someone comes calling.
As you may know to your cost, the sound produced by a door knocker does not always carry well inside, particularly if the internal doors are closed and the TV is on: what you need is a far more versatile announcing system — an electric doorbell.
The great advantage of an electric bell is that you can site it where it can be most easily heard. You can fit an extension bell to make the system more audible, and have bell pushes for both front and back doors.
Types of bells: Electric bells operate off very low voltages and the simplest types are battery powered. They’re available individually or in kits, complete with a length of special thin two-core (twin) bell wire to connect to the power source, a bell push and all the fixings. You should be able to install a simple battery powered bell system in about half an hour.
Doorbells can also be powered from the mains, but you must fit a suitable transformer to reduce the mains voltage. If you decide on this system, you’ll find there’s a wider range of bells to choose from, but the initial costs are inevitably higher: a bell transformer can cost more than the bell kit itself. Installation will also take longer, because you have to make a connection into the mains supply.
Both battery and mainspowered electric bells are cheap to run.
Batteries last about two years while a mains powered bell will have little effect on your electricity bill.
Buying a bell
When you go to buy a bell, visit a store with several different types on ‘live’ display so that you can try them out and buy the one that suits you best. Bells, buzzers and chimes are all available while the more complex types can play a short peel and some models containing a cassette or programmed microprocessor can play a short tune.
If you want to fit two bell pushes, it’s worth considering a unit which gives one signal for the front door and a slightly differ ent one for the back.
A simple chime unit consists of an electromagnet wound round a sliding bar; at each end there’s a striking plate or tube — these often hang down below the housing. When the bell push is depressed, the bar is drawn through the electromagnetic coil to strike one of the tubes. It’s held in this position until the bell push is released when a spring throws the bar back through the coil to hit the chime tube on the other side — hence the familiar ‘dingdong’. Some models also incorporate a ‘repeater’ mechanism for keeping this action going as long as the bell push is depressed.
Probably the most familiar of doorbells is the ‘trembler’ bell, so called because the sound it makes is created by a hammer vibrating furiously against a metal gong. The bell will continue to ring as long as the bell push is kept down.
With trembler bells, an electromagnet is again used to activate the striking arm, but as the arm moves ‘makeandbreak’ contacts are opened, so closing the circuit. The arm returns to its starting position once it has struck the gong. Because the make andbreak contacts are now closed, the circuit is remade so the process repeats itself — at many times a second — until the circuit is finally broken when the bell push is released; the volume of the bell can be adjusted via a screw on the makeand break contacts.
Trembler bells can operate off of the direct current (DC) of batteries or the alternating
current (AC) of the mains via a transformer. But you can also buy mainsoperated trembler bells, which harness the alternating nature of the current to cause the hammer to vibrate against the gong. These bells don’t require makeandbreak contacts so they’re much easier to maintain.
If you aren’t keen on a piercing ringing bell, then you can opt for a buzzer instead. This works in a similar way to the trembler bell, but the sound is made by a metal bar striking the electromagnet itself, rather than a gong. Again, battery and mains types are made.
To operate any doorbell you need a basic switching mechanism and this, simply, is what a bell push is. When you push the button you complete the circuit made with the bell wire; when you remove your finger a spring pushes the contacts apart.
The most basic types consist of a plastic base plate on which the switch mechanism is
mounted; this is protected by a pushon cover, which also conceals the fixing screws. You can also buy brass and other ornate bell pushes to match your door furniture: they work in exactly the same way as the basic type. Some of the more elaborate pushes include a light, which illuminates the button or a name tag; useful features on a poorly lit doorstep. Because the light will stay on con tinuously illuminated pushes should only be used when the bell is run off the mains; a battery would run flat within two or three days. The miniature bulb inside may require occasional replacement.
Choosing a transformer
It’s safest and easiest to buy a purposemade transformer for your bell. These units normally contain 1A fuse. The instructions with the bell will tell you what voltage it should be run on — commonly 3, 5 or 8 volts — and you’ll find that most bell transformers have output (Secondary) terminals to match. Chimes usually have to be connected to the 8V terminals; bells and buzzers to the 5 or 3V terminals. You can also get transformers which supply higher voltages — commonly 4, 8 and 12 volts.
Siting the housing
Obviously, the bell push will have to be sited right by the door.
The best place to site the bell housing is often in the hall where it can probably be heard throughout the house. An extension bell can be installed in a garage or shed, and if someone is hard of hearing then it’s also worth putting another bell in the living room, kitchen or other room that’s used frequently.
Mount the bell high up on the wall so that it’s inconspicuous and can’t be knocked accidentally. This is particularly important for chimes with striking tubes that protrude down from the housing.
Once you’ve determined the site, you can work out how you’re going to run the bell wire to the bell push, and to the transformer. Fortunately, because bell wire is very thin it’s easy to conceal behind picture rails, skirting boards and architraves.
There are basically four ways to connect your transformer. The simplest is to plug it into a threepin socket outlet, replacing the plug’s 13A fuse with a 3A one instead. But to avoid an unsightly run of flex, the transfomer should be fitted next to the socket and this leaves it vulnerable to knocks. In addition, hallways, where bells are usually installed, tend to be short of sockets and you may have to unplug the transformer each time you want to operate your vacuum cleaner for example. To get around this, you could install a switched fused connection unit, fitted with a 3A fuse, specifically for the transformer. This unit should be connected to a spur run in 2.5m2 twocore and earth cable from the main power circuit; then 1.0mm2 twocore and earth cable should be run to the primary terminals of the transformer itself.
Similarly, you could break into the lighting circuit either by linking into a loopin ceiling rose or by running a branch from a new three terminal joint box installed on the supply cable.
Unfortunately, to carry out the wiring you’ll have to raise a few floorboards.
However, this does allow you to mount the transformer neatly by the side of the bell housing, especially if it’s set high up on the wall. But as you’re likely to be installing the bell close to the consumer unit — usually in the hallway — it makes sense to make your mains connection here.
If your consumer unit has a spare fuse-way or spare miniature circuit breaker (MCB) the best way to obtain power for the transformer is to connect it to its own circuit protected by a 5A fuse or MCB.
Electricity is potentially lethal if you don’t treat it properly.
So long as you make sure that the current is switched off before you touch any electrical fitting you cannot possibly get a shock.
But, although turning off the main switch will render the live parts dead, in some consumer units the mains terminals to which the meter, leads connect aren’t recessed, and there’s still a risk of you receiving a shock. To be safe, it’s wise to ask the electricity board to cut off the mains supply before you carry out any work on the consumer unit. When they restore the power they can also test your new circuit.
INSTALLING A BELL PUSH AND HOUSING
When it comes to fitting a mains powered door bell, all the work entails is installing a simple electric circuit. This consists of the bell push to activate the circuit, the wire to carry the current to the bell itself — and a transformer to provide the correct voltage.
Start by fitting the bell push. This is normally sited on the door frame at about chest height. It should be conspicuous, yet protected from the weather.
IlkBed the bell push on nonsetting mastic if there’s a danger that it might be exposed to rain.
Hold the backplate of the unit to the frame and mark the position of the fixing holes and
the bell wire entry using a bradawl. Then drill a 6mm diameter hole through the frame so the bell wire can be fed into the back of the push. Screw the backplate in place using woodscrews — they’re usually provided —and thread the bell wire through the hole in the door frame.
Separate the two insulated wire cores enough to allow them to reach the terminals on the backplate. Strip about 6mm of insula tion from each of the cores and connect them to the terminals (it doesn’t matter which way round they go), using a small electrician’s screwdriver. Now draw any extra bell wire back through the hole — avoid straining the connections — and then clip on the bell push cover.
Next run the bell wire back to the site of the bell housing choosing the most inconspicuous route, usually along skirting and picture rails and around door frames.
TIP: If the bell wire is kinked, running it quickly through your hands a few times will warm and smooth it.
Keep the wire in place at 600mm intervals either with bell wire tacks, which you tap between the insulated cores, or with small cable clips that lap over both cores. You can also buy bell wire with a sticky strip on one side that you just press down to hold in place.
Remove the decorative cover from the bell housing and hold the backplate, which contains the bell mechanism, against the wall.
Mark the fixing holes using a bradawl then drill and plug them.
Run the bell wire from the push to the housing. Separate and strip back the insulation of the cores then connect them to the relevant terminals. TIP: Before screwing the backplate in position, you may find it easier to feed in the bell wire from the push.
Fix the backplate, and connect to the transformer, then replace the cover.
INSTALLING A BELL TRANSFORMER
The transformer reduces the mains voltage to the low level required for a doorbell. There are various ways to connect it — from simply plugging it into the mains at a threepin socket to providing its own circuit from the consumer unit.
A bell transformer has two sets of terminals. At the top of the box the ‘primary’ terminals take the cable linking into the 240V mains supply; at the bottom the ‘secondary’ terminals take the twin bell wire from the bell housing. Make the connections by attaching the exposed bell wire cores to the correctly rated screw down terminals.
To connect into a spare fuse-way in the consumer unit, first turn off the main switch (or
have the mains supply cut off temporarily); remove the consumer unit cover and check that there’s a spare (unconnected) fuseway the correct rating for the transformer: 5A. RtIP If there’s not ‘a spare fuseway, you’ll have to unscrew the live busbar and slide the existing fuseways along the busbar to make room for a new one. The fuseways must be arranged in the correct current rating sequence: highest (45A) next to the main switch; the lowest (5A) at the opposite end.
Once you have the correctly rated fuse way installed, mount the transformer next to the consumer unit.
Attach a length of twin bell wire to the secondary terminals of the transformer and run it to the bell housing. Make the connections and attach the decorative cover.
Strip and connect the live (red) and the black (neutral) cores of a length of 1.0mm’ twocore and earth cable to the primary terminals of the transformer. If the transformer doesn’t need to be earthed, then ignore the earth core and tape it back out of the way.
It’s best to make all the connections from the push to the bell housing and on to the transformer — before you make the mains connections. This lessens the time you’ll have to have the power switched off.
Run the cable to the entry point of the consumer unit, fastening it down with cable clips. Remove enough of the cable’s outer sleeve so there’s about 25mm remaining inside the box. Strip off about 10mm of insulation from each core. Connect the live core to the terminal at the top of the spare fuseway and take the neutral core to the neutral block. Link the earth core (which must be sleeved in green/yellow PVC) to the earth terminal.
Have the supply restored and turn on the main switch. Test the bell to ensure that everything works properly.
Australian and New Zealand laws prohibit doityourselfers from doing most electrical work.
If you don’t want to go to the trouble and expense of fitting a transformer, a batteryoperated doorbell is the answer. With most chimes and some bells, the batteries fit inside the unit.
Rather than using one large battery, usually two or four 11/2V ‘baby’ or ‘mono’ batteries are used instead. These are arranged in series to give the required voltage. They’re slotted into place against spring terminals, and the direction in which they should be set is clearly marked with arrows and positive and negative symbols. The doorbell won’t function unless the batteries are the right way round.
High power (HP) batteries last longer than ordinary ones: make sure you use the sealed type to reduce the risk of leakages.
When the batteries run down, change them immediately — don’t leave them in the unit, where they may corrode.
Many bells and most buzzers don’t make provision for the batteries to be housed internally. Instead they run off a larger battery (usually 4 ½ V) which have to be mounted nearby.
To wire up a bell to a battery, connect a length of twin bell wire to the terminals inside the bell or buzzer unit. Run one core to the bell push and then link a separate single core from the push to the negative (-) terminal of the battery. The two cores of the bell wire are easy to separate simply by pulling them apart. Next run a single core of bell wire from the positive ( + ) terminal of the battery to connect up the free end of the bell wire from the bell housing.
Join the single core of bell LIP, Join by stripping back a little insulation and then twist the strands together. Secure with a blob of solder then wind PVC insulating tape round it.
You can’t connect two trembler bells together if the circuit is run off batteries: the first bell would prevent the second one from operating properly. To get round this problem either fit an AC powered bell or join the makeandbreak contacts of the second bell with a core of bell wire.
You’ll need twice the voltage to power an extension bell. Either fit a more powerful battery or connect two 4 1/2V batteries in series (negative to positive) with bell wire.
You might not be able to hear the front doorbell from certain parts of the house —especially if the internal doors are shut, or you’re in the garden. The answer here is to fit an extension bell.
You can either wire the two bells in ‘series’ or in ‘parallel’. The advantage of the first method is that the two bells are connected in the same circuit, so one bell won’t rob the other of power. You’ll need to reconnect the bell wire in the transformer to higher voltage terminals.
To wire two bells in series:
connect the push to the transformer with a single core of bell wire
connect the push to one bell with a single core of bell wire join the two bells with another single core run a single core from the second bell to the transformer.
The advantages of bells wired in parallel is that if one breaks down the other will still work. Both bells must be of the same type and while strictly you don’t have to double the operating voltage, it is advisable to do so.
To wire two bells in parallel:
connect twin bell wire to the transformer
split one core and connect up the push
run the twin bell wire on to the first bell
run a further length of twin bell wire on to the second bell and make the connections.