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Fuse or mcb L Live Electricity in Fuse or mcb L Live N Neutral E Earth Home Electricity in The second circuit is used where there are two switches, for example at each of two doors to a room. The type of switch used is called a two-way switch and, if the light is off, as drawn, either switch will switch it on. If the light is on, either switch can switch it off. Examine the circuit and see why this is so. the N Neutral How is electricity supply delivered to a house? L Live N Neutral the Fuse or mcb Socket 1 Socke The ESB maintains a national network of high tension power Fuse or mcb L Live lines. The voltages on these lines are as high as 400 kV. Such The second circuit is used where there are two switches, for example at voltages are not delivered to domestic premises. Instead the Two-way switch Fuse or mcb L Live each of two doors to a room. The type of switch used is called a two-way voltage is stepped down at transformers to a more suitable E Earth switch and, if the light is off, as drawn, either switch will switch it on.N Neutral If the NNeutral lower value. A two-wire cable is used to bring electricity to light is on, either switch can switch it off. Examine the circuit and see why Fig. the home. neutral is connected a metal plate in thetension power The ESBThe maintains a nationaltonetwork of high this is so. ground, and so is at 0V. Therefore, the neutral is said to be Fig.3 Lighting circut, two two-way switches lines. The voltages on these lines are as high as 400 kV. Such Other circuits earthed. The voltage on the live wire alternates to 311V above voltages are50not delivered domestic premises. the and below this times a secondto giving an effective 220V. Instead Live L Fuse or mcb OtherTwo-way types ofswitch domestic load use larg Lighting circuits do not require large currents. Typically, a circuit breaker independent radial circuits which are not or fuse of 6 amps is used. The conductors in lighting cables therefore Atvoltage the house, main fuse and meter installed. transformers to a more suitable isastepped down at are How is electricity supply delivered to a house? need not be very thick. One 100 Watt bulb uses less than half an amp as The most common are immersion (wat NNeutral lower value. A two-wire cable is used to bring electricity to showers. Cookers and showers require shown below. How is electricity distributed in thetohouse? the home. The neutral is connected a metal plate in the Fuse or mcb L Live IV = Power 0.45 A x 220V = 100 W The cable is then terminated on a consumer unit. From the consumer unit Why use fuses and mcb ground, and so is at 0V. Therefore, the neutral is said to be Socket 1 Socket 2 different circuits are run to the various points where electricity is needed Fig.3 Lighting circut, two two-way switches A fuse is a wire that will get hot and mel Neutralprotect a circuit feeding more than Therefore, - lights, sockets, cookers etc. These are allwire fed with the 220V fromto 311V earthed. The voltage oncircuits the live alternates abovea 6 amp mcb couldN safely rated current. By melting, the fuse disco ten 100 W bulbs. In practice, the lighting circuits for a number of rooms are the consumer unit, so all domestic circuits are in parallel. Fuse or mcb L Live reducing the of overheating and below this 50 times a second giving an effective 220V. connected in parallel and supplied throughdo onenot mcb. It is not large convenient Lighting circuits require currents. Typically, a risk circuit breaker and fire The live wire connection to every circuit is fed through a safety device Neutral Nhave to all lights fail at the same time so it is common to have two or more Like a fuse, a miniature circuit breaker or fuse of 6 amps is used. The conductors in lighting cables therefore At the house, fuse and meter installed. which cuts off the circuitaif main the current demanded becomesare excessive. This E Earth lighting circuits in a house. is toohalf large. is a switch need not be very thick. One 100 Watt bulb usescurrent less than anItamp as with Circuit breakers are faster and more pre shown below. reset. The circuit breakers on a distribu can be a fuse or a miniature circuit breaker (mcb). How is electricity distributed in the house? Power circuits for appliances (sockets) Fuse or mcb L Live are called miniature circuit breakers. A xa220V = 100 W The term appliance is a general term IV for = anyPower thing powered0.45 through The cable is then terminated on a consumer unit. From the consumer unit plug and a flexible cable. The standard plug is designed to carry up to Socket 13 1 Socket 2 different circuits are run to the various points where electricity isamps, needed What is a residual curre though most appliances need considerably less. Inside the plug Neutral N Therefore, a 6 amp mcb safely protect a circuit feeding more than - lights, sockets, cookers etc. These circuits are all fed with the 220V from there is a fuse. The fuse is usually either a 3-amp fusecould (for appliances up One device that reduces the likelihood of h ten 100 In practice, the3lighting circuits for a number rooms to 660 Watts) or a 13-amp fuse W (forbulbs. appliances up to almost kilowatts). the consumer unit, so all domestic circuits are in parallel. Electricity entersof and leavesare a house th Fuse or mcb LALive Where a 3-amp fuse isconnected sufficient it should be used. fault then is more in parallel and supplied through oneNormally, mcb. It the is not convenient amount of electricity ent likely to blow this fuse only, rather than both blow it and also trip the mcb The live wire connection to every circuit is fed through a safety device Neutral same amount there is a fault toNhave all lights fail at the same time so it is common to haveleaving. two orIf more Two-way switch L1Live Fuse orSocket mcb on the This consumer unit. Socket 2 Socket 3 Socket 4 electricity from a live wire going to earth which cuts off the circuit if the current demanded becomes excessive. E Earth lighting circuits in a house. is called a residual current or an earth-le In general, almost all the power consumed in a house is converted into can be a fuse or a miniature circuit breaker (mcb). NNeutral Fig.1 Image of consumer unit and meter The conductors in the circuit are copper and are insulated. The resistance must be low enough that, • at the rated current, the drop in voltage between the consumer unit and the load is low • the copper does not get too hot. Cables with large diameters have less resistance than those with smaller diameters. In general, domestic circuits are classified as lighting circuits or power circuits. Fuse or mcb L Live heat. Appliances that generate a lot of heat, like electric fires or kettles, use large currents and consume a lot of power. At 220V, the current per kilowatt is about 4.5 amps. Many other appliances such as radios or mobile phone chargers need little power. A fault current to earth has implications. smaller current, 30 mA, can kill a p Power circuits for applianceseven(sockets) The RCD consists of a circuit breaker The term appliance is a general term for any thing powered through a entering and leaving on the live and ne N Neutral E Earth When sockets are fittedplug as shown the circuit is called radial circuit. and below, a flexible cable. The astandard plug is designed to carry up usually to 13 also tri mA. Domestic RCDs will (It radiates out from theamps, consumer unit.) Because each socket can supply 63 A, is exceeded. though most appliances need considerably less. Inside the plug 13 amps there is a limit to the number of sockets that can be supplied by there is a fuse. The fuse is usually either a 3-amp (forforappliances Thefuse current most or all ofup the circuit one cable. which is between the main fuse and to 660 Watts) or a 13-amp fuse (for appliances RCD up to almost 3 kilowatts). Fig.4 A radial circut with two sockets Where a 3-amp fuse is sufficient it should be used. A fault then is more Socket 1 likely to blow this fuse only, Socket rather2 than both blow it andis also tripearth the mcb What the rod? Two-way switch Fuse orSocket mcb L1Live on the consumer unit. Socket 2 Socket 3 Socket 4 The earth wire in a domestic circuit is co How lighting circuits are connected Fuse or mcb L Live ground which provides a low-resista In general, almost all the power consumed in athehouse is converted into NNeutral the transformer. At the transformer, the Fuse or mcb Live L heat. Appliances that generate a lot of heat, like firesis why or kettles, E Earth theelectric ground. This electricity will flo use large currents and consume a lot of power. At 220V, the current per Fig.1 Image of consumer unit and meter Fuse or mcb L Live kilowatt is about 4.5 amps. Many other appliances such as radios or An alternative approach is the ring circuit. Here the circuit takes the form mobile phone chargers need little power. The conductors in the circuit are copper and are insulated. The resistance of a ring with both ends of the ring connected to the consumer unit. Both N Neutral N Neutral Earth must be low enough that, “live” wires are connected to one E mcb, both neutrals to the neutral, both When sockets are fitted as shown below, the circuit is called a radial circuit. earths to earth. This has the advantage that the current demanded can • at the rated current, the drop in voltage between the consumer unit (It radiates out from the consumer unit.) flow two ways and is spread over two conductors. A ring circuit canBecause each socket can supply Fig.2 and Lighting switch thecircut, load one is low contain more sockets 13 thanamps two radial circuits. there is a limit to the number of sockets that can be supplied by one cable. • the copper does not get too hot. Two simple lighting circuits are shown below. The first circuit is used where there is a single switch, usually at the door of a room. N Neutral Cables with large diameters have less resistance than those with smaller diameters. In general, domestic circuits are classified as lighting circuits or power circuits. Fuse or mcb SocketA1radial Socketcircut 2 Socket 3 Socket 4 Fig.4 with two sockets Socket 1 How lighting circuits are connected Two simple lighting circuits are shown below. The first circuit is used where there isFuse a single usually at the door of a switch room. Two-way L Live or mcb switch, FuseNNeutral or mcb L Live Fuse or mcb E Earth L Live N Neutral N Neutral E Earth An alternative approach is the ring circuit. Here the circuit takes the form of a ring with both ends of the ring connected to the consumer unit. Both “live” wires are connected to one mcb, both neutrals to the neutral, both earths to earth. This has the advantage that the current demanded can flow two ways and is spread over two conductors. A ring circuit can contain more sockets than two radial circuits. N Neutral Fig.2 Lighting circut, one switch Socket 1 Socket 2 L Live Socket 2 Socket 1 Socket 2 Socket 3 Socket 4 the Socket 2 Fuse or mcb Fuse or mcb Fuse or mcb L Live L Live N Neutral N Neutral L Live N Neutral Electricity in the Socket 1 E Earth Home E Earth Home How is electricity supply delivered to a house? The ESB maintains a national network of high tension power lines. The voltages on these lines are as high as 400 kV. Such voltages are not delivered to domestic premises. Instead the more3suitable voltage is stepped down Socket at transformers 1 Socket to 2 aSocket Socket 4 lower value. A two-wire cable is used to bring electricity to the home. The neutral is connected to a metal plate in the Fuse or mcb L Live ground, and so is at 0V. Therefore, the neutral is said to be earthed. The voltage on the live wire alternates to 311V above and below this 50 times a second giving an effective 220V. At the house, a main fuse and meter are installed. N Neutral E Earth The second circuit is used where there are two switches, for example at each of two doors to a room. The type of switch used is called a two-way switch and, if the light is off, as drawn, either switch will switch it on. If the light is on, either switch can switch it off. Examine the circuit and see why this is so. Socket 1 Socke Fuse or mcb L Live Two-way switch Fuse or mcb L Live E Earth NNeutral N Neutral Fig. Fig.3 Lighting circut, two two-way switches Other circuits Lighting circuits do not require large currents. Typically, a circuit breaker or fuse of 6 amps is used. The conductors in lighting cables therefore need not be very thick. One 100 Watt bulb uses less than half an amp as shown below. How is electricity distributed inAthe Fig.5 ring house? circut with four sockets What L Live is ESB Customer Supply? 0.45 A x 220V = 100 W Fuse or mcb IV = Power The cable is then terminated on a consumer unit. From the consumer unit different circuits are run to the various points where electricity is needed - lights, sockets, cookers etc. These circuits are all fed with the 220V from the consumer unit, so all domestic circuits are in parallel. Other types of domestic load use larg independent radial circuits which are not The most common are immersion (wat showers. Cookers and showers require Socket 1 Socket 2 Why use fuses and mcb ESB Customer Supply supplies electricity toa wire 1.8 that million A fuse is will get hot and mel Neutralprotect a circuit feeding more than Other circuits Therefore, a 6 amp mcb couldN safely rated current. By melting, the fuse disco customers (on the basis published tariffs). It provides ten 100 W bulbs. In practice, the lighting circuits for a number ofof rooms are or mcb L Live reducing the risk of overheating and fire Other types of domestic load use large currents and are supplied byFuse connected in parallel and supplied through one mcb. It is not convenient customers with services which meet their needs (for The live wire connection to every circuit is fed through a safety device Neutral toNhave all lights fail at the same time so it is common to have two or more independent radial circuits which are not connected to any other appliance. Like a fuse, a miniature circuit breaker which cuts off the circuit if the current demanded becomes excessive. This Earth E circuits in a house. example, budget accounts, direct debit and other current is too payment large. It is a switch with The most arecircuit immersion (water) heaters, cookers and lighting electric can be a fusecommon or a miniature breaker (mcb). breakers are faster showers. Cookers and showers require very thick conductors. options) and with appropriate advice Circuit to help them use and more pre reset. The circuit breakers on a distribu Power circuitselectricity for appliances (sockets) more efficiently while saving money at circuit the breakers. are called miniature The term appliance is a general term for any thing powered through a Why use fuses and mcbs? same time. plug and a flexible cable. The standard plug is designed to carry up to 13 What is a residual curre amps, its though most appliances need considerably less. Inside the plug A fuse is a wire that will get hot and melt (“blow”) if the circuit is above Customer Supply approximately 650 people there is a fuse. The fuseESB is usually either a 3-amp fuse (foremploys appliances up One device that reduces the likelihood of h rated current. By melting, the fuse disconnects the live wire from the load, to 660 Watts) or a 13-amp fusein(for appliances up toissues almost 3 11 kilowatts). Electricity enters andover leaves a house th and any one year million bills and handles reducing the risk of overheating and fire. Where a 3-amp fuse is sufficient it should be used. A fault then is more Normally, the amount of electricity ent 3 million telephone from customers. likely to blow this fuse only, rather than both blow it calls and also trip the mcb same amount leaving. If there is a fault Two-way switch Fuse orSocket mcb L1Live Like a fuse, a miniature circuit breaker disconnects the live wire on if thethe consumer unit. Socket 2 Socket 3 Socket 4 electricity from a live wire going to earth current is too large. It is a switch with contacts that open very quickly. As a business unit within ESB, into Customer Supply hascurrent over or an earth-le is called a residual In general, almost all the power consumed in a house is converted NNeutral Circuit breakers are faster and more precise than fuses and theyheat. can or be Fuse mcb L Live Appliances that generate a lot of heat, like electric fires or kettles, 75 years experience in providing electricity services to implications. A fault current to earth has reset. The circuit breakers onImage a distribution very compact and currents and consume a lot of power. At 220V, the current per use large Fig.1 of consumerboard unit andare meter even smaller current, 30 mA, can kill a p customers throughout Ireland. kilowatt is about 4.5 amps. Many other appliances such as radios or are called miniature circuit breakers. The RCD consists of a circuit breaker entering andmarkets leaving on in the live and ne Ireland has one of the fastest-growing electricity N Neutral E Earth When sockets are fitted as shown below, the circuit is called a radial circuit. mA. Domestic RCDs will usually also tri • at the rated current, the drop in voltage between the consumer unit (It radiates out from the consumer unit.) Because each socket can over supply 40 per the developed world. It grew cent over the last 63 A, is exceeded. and the load is low 13 amps there is a limit to the number of sockets that can be supplied by 10 years, far ahead of average growth in The thecurrent rest of for Europe. most or all of the circuit One device reduces thehot. likelihood of harm from electric shock is the oneRCD. cable. • the copperthat does not get too RCD which is between the main fuse and The market has been fully opened to competition since Electricity enters and leaves a house through thewith live and neutral wires. Cables with large diameters have less resistance than those smaller Fig.4 A radial circut with two sockets diameters. Inthe general, domestic circuits are classified circuitsby exactly the Normally, amount of electricity enteringasislighting matched February 2005.Socket 1 Socket 2 or power circuits. leaving. If there is a fault however, it often involves some What is the earth rod? same amount The conductors in the circuit are copper and are insulated. The resistance must be low enough that, mobile phone chargers need little power. What is a residual current device (RCD)? electricity from a live wire going to earth, possibly through a person. This How connected is calledlighting a residualcircuits current or are an earth-leakage current. Two simple lighting circuits are shown below. The first circuit is used where Fuse or mcb You can L Livefind N Neutral Athere fault to earth hasatimplications. Even 100 mA can cause a fire. An is acurrent single switch, usually the door of a room. even smaller current, 30 mA, can kill a person. Fuse or mcb The earth wire in a domestic circuit is co out more about ESB Customer Supply bywhich logging the ground provides a low-resista onto www.esb.ie and www.sciencetechnologyaction.com the transformer. At the transformer, the E Earth the ground. This is why electricity will flo L Live An alternative approach is the ring circuit. Here the circuit takes the form The RCD consists of a circuit breaker which is tripped if the currents of a ring with both ends of the ring connected to the consumer unit. Both entering and leavingNon the live and neutral wires differ by more “live” than wires 30 are connected Be careful withto electricity Neutral to one mcb, both neutrals the neutral, both mA. Domestic RCDs will usually also trip if a certain current, for example earths to earth. This has the advantage that the current demanded can flow two ways and is spread over two conductors. ring circuit can 63 A, is exceeded. ‘Electricity is so much aA part of modern living that we can often Fig.2 Lighting circut, one switch contain more sockets than two radial circuits. take it for granted. It is a powerful and versatile energy but can be The current for most or all of the circuits in modern houses is fed via an dangerous if not used properly.’ RCD which is between the main fuse and their mcbs or fuses. Socket 1 Socket 2 Socket 3 Socket 4 What is the earth rod? Fuse or mcb The earth wire in a domestic circuit is connected to an earth electrode in the ground which provides a low-resistance path via the ground itself to the transformer. At the transformer, the neutral is connected to a plate in the ground. This is why electricity will flow from live to earth. Two-way switch Fuse or mcb L Live NNeutral Serious accidents with electricity in the home are rare but each year L Livethere is a small number of fatalities and serious injuries. Most of the accidents that occur are due either to carelessness or to a lack of awareness of some basic rules that should always be observed when using electricity.’ E Earth N Neutral The above is an extract from the booklet The Safe Use of Electricity in the Home which is produced by the ESB in cooperation with the Electro Technical Council of Ireland. The booklet contains essential information on electrical safety in general and also hints and rules which you should always follow. The booklet is available on www.esb.ie. Socket 1 Socket 2 Fuse or mcb L Live L Live N Neutral Electricity in E Earth Home Electricity in How is electricity supply delivered to a house? The ESB maintains a national network of high tension power lines. The voltages on these lines are as high as 400 kV. Such voltages are not delivered to domestic premises. Instead the voltage is stepped down at transformers to a more suitable Syllabus Reference lower value. A two-wire cable is used to bring electricity to the home. The neutral is Physics: connected to a metal plate in the Leaving Certificate ground, and7, soDomestic is at 0V. Therefore, Electricity circuits the neutral is said to be earthed. The voltage on the live wire alternates to 311V above and below this 50 timesScience: a second giving an effective 220V. Junior Certificate At the house, a main fuse and are installed. Section 3C5, Electricity in meter the home How is electricity distributed in the house? The cable is then terminated on a consumer unit. From the consumer unit different circuits are run to the various points where electricity is needed - lights, sockets, cookers etc. These circuits are all fed with the 220V from the consumer unit, so all domestic circuits are in parallel. The live wire connection to every circuit is fed through a safety device which cuts off the circuit if the current demanded becomes excessive. This can be a fuse or a miniature circuit breaker (mcb). Learning Objectives The second circuit is used where there are two switches, for example at each of two doors to a room. The type of switch used is called a two-way switch and, if the light is off, as drawn, either switch will switch it on. If the light is on, either switch can switch it off. Examine the circuit and see why this is so. Socket 1 Socke Fuse or mcb L Live Two-way switch Fuse or mcb L Live Activities E Earth NNeutral • the N Neutral the Fuse or mcb N Neutral Energy saving devices make sense, look at the difference in running costs for a CF and incandescent bulb. Fig. Fig.3 Lighting circut, two two-way switches Other circuits If you are watching the light from a lamp when a kettle, or something types ofmay domestic load use larg Lighting circuits do not require currents. Typically, else, large is also switched on, aacircuit smallbreaker reduction in Other brightness be seen. circuits which or fuse of 6 amps is used. The conductors lighting cables therefore Ohm’s law saysinthat if the current through a independent resistanceradial increases the are not The most common are immersion (wat need not be very thick. One 100 Watt bulb uses less than half an amp as voltage across it increases. It seems strange to think of the conductors showers. Cookers and showers require shown below. as a resistance but they are and the 220V supply in the house is Fuse or mcb L Live IV = Power reduced 0.45 by A x the 220Vvoltage = 100 Wdrop caused by the extra Whycurrent. use fuses and mcb • Socket 1 Socket 2 A electricity fuse is a wire willelectric get hot and mel Neutral N safely • could In the 1950s, it was common for a ruralthan house with tothat have Therefore, a 6 amp mcb protect a circuit feeding more ratedHow current. Bylife melting, the fuse disco ten 100 W bulbs. In practice, the lighting circuits and, for a number of rooms are lights, one socket possibly an electric cooker. has changed Fuse or mcb L Live reducing the risk of overheating and fire connected in parallel and supplied through one mcb. It is not convenient in the last 50 years? How many sockets are there in your home? Neutral toNhave all lights fail at the same time so it is common to have two or more Like a fuse, a miniature circuit breaker E Earth lighting circuits in a house. current too large.switches. It is a switch with • Consider the second lighting circuit which has two is two-way Circuit breakers faster and more pre If a third (or even a fourth or fifth) switch is required, this are is possible On completing this section, the student should be able to: reset. The circuit breakers on a distribu Power circuits for appliances (sockets) by inserting a different type of switch in the are circuit between the twocalled miniature circuit breakers. • Describe the ideas behind electricity distribution and use in The term appliance is a general way switches. This switch is called term for any thing powered throughan a intermediate switch. It has four the home plug and a flexible cable. The standardYou plugcan is designed to carry up as to 13 terminals. insert as many you wish. Can you guess what an What is a residual curre amps, though most appliances need considerably less. Inside the plug intermediate switch does? • Outline some safety aspects of using electricity there is a fuse. The fuse is usually either a 3-amp fuse (for appliances up One device that reduces the likelihood of h to 660 Watts) or a 13-amp fuse (forthe appliances up to almost kilowatts). • Check cable attached to3an appliance. ItElectricity usually enters has three wires. and leaves a house th • Identify different types of circuits and protective devices Where a 3-amp fuse is sufficient it should be used. A fault then is more Normally, Looking the amountinto of electricity ent These are coloured brown, blue and green/yellow. the likely to blow this fuse only, rather than both blow it and also trip the mcb amount leaving. If there is a fault Two-wayoff, switchthere aresame L1Live Fuse orSocket mcb plug when the back is4 taken three pins and a cord • State the formula relating power, voltage and current on the consumer unit. Socket 2 Socket 3 Socket electricity from a live wire going to earth grip visible. The green yellow earth wire is isconnected to the pinorin called a residual current an earth-le In general, almost all the power consumed in a house is converted into NNeutral the top neutral wire is blue and connected to the pin on Fuse or mcb L Live heat. Appliances that generate a lotcentre. of heat, The like electric fires or kettles, A fault current to earth has implications. the lefta lot (normally “N”). The the smaller right is the 30 livemA, pin use large currents and consume of power. marked At 220V, the current perpin on even Fig.1 Image of consumer unit and meter current, can kill a p kilowatt is about 4.5 amps. appliances as radios andMany it isother connected tosuch a fuse. The orother end of the fuse (normally The RCD consists of a circuit breaker mobile phone chargers need little power. The conductors in the circuit are copper and are insulated. The resistance marked “L”) is connected to the brown live wire. When wiring a plug entering and leaving on the live and ne N Neutral E Earth must be low enough that, When sockets are fitted asitshown below, the circuit is called a radial is important that the cord gripcircuit. grips the outer sheath RCDs and not just also tri mA. Domestic will usually • at the rated current, the drop in voltage between the consumer unit (It radiates out from the consumer unit.)Some Becauseappliances each socket can supply A, is exceeded. the wires. only have two 63 wires, brown and blue. and the load isLearning low 13 amps there is a limit to the number of sockets that can be supplied by General Points Connect them as above. The current for most or all of the circuit one cable. • the copper does not get too hot. • Small electric currents kill. Cables with large diameters have can less resistance than those with smaller diameters. In general, domestic circuits are classified as lighting circuits or circuits. • power People conduct electricity. A typical person has a RCD which is between the main fuse and Fig.4 A radial circut with two sockets resistance of between 1.5 kΩ and 5 kΩ. It varies with the individual and whether How thelighting skin is wetcircuits or not. are connected Two simple lighting circuits are shown below. The first circuit is used where there is a single switch, usually the7mA door of a room. • Even a current as lowatas can prevent the victim from • True or False Fuse or mcb N Neutral letting go. L Live Indicate whether the following are E Earth by drawing a circle around T or F. What is the earth rod? The earth wire in a domestic circuit is co the ground which provides a low-resista truethe(T) or false (F)transformer, the transformer. At the the ground. This is why electricity will flo T F T F Fuses do not protect people than T F T F (e) A 6A fuse can cater for 10 100W bulbs T F (f) People good insulators Socket 1 are Socket 2 Socket 3 Socket 4 T F (g) When switched on, a kettle uses less electricity than a 100W bulb (the bulb is obviously much hotter). T F (h) All domestic circuits are in series T F T F (j) The fuse in a plug is in series with the live wire T F (k) A 6A fuse can cater for a 2.5 kW kettle T F (l) Big fuses are best because they blow less often T F personcircut, is much lower Fig.2a Lighting one switch • Socket 2 (a) Fuses protect people from shocks Fuse or mcb L Live and For a resistance of 1.5 kΩ the current would be about 150 mA An alternative approach is the ring circuit. Here the circuit takes the form the ring connected the consumer unit. Both (b)ofYour electricity billtocharges for the total voltage you have used from arm to arm through the heart. This is likely to be fatal. of a ring with both ends N Neutral • Socket 1 “live” wires are connected to one mcb, both neutrals to the neutral, both green/yellow wire in a plug goes can to the earth pin at the top earths to earth. This (c) has The the advantage that the current demanded from shocks, the current required to kill flow two ways and is spread over two conductors. A ring circuit can the rating of any household fuse.contain more sockets(d) A two-way switch is needed to light two bulbs at the same time than two radial circuits. For simplicity, no earth wire was shown in the lighting circuits but metal light fittings must be earthed. • Most electricity is converted into heat. Where a lot of heat is generated, Fuse or mcb a lot of electricity (energy) is consumed. • 220 V is an effective mean, the peak voltage is 311 V (220 x √2) because the neutral is earthed it is at 0V. Two-way switch Fuse or mcb L Live NNeutral L Live (i) NModern Neutral E Earth supplies will cut off if an earth-leakage of 50 mA is detected Check your answers to these questions on www.sciencetechnologyaction.com Socket 1 Socket 2 the Fuse or mcb L Live L Live N Neutral N Neutral Electricity in the Fuse or mcb E Earth Home Home How is electricity supply delivered to a house? The second circuit is used where there are two switches, for example at each of two doors to a room. The type of switch used is called a two-way switch and, if the light is off, as drawn, either switch will switch it on. If the light is on, either switch can switch it off. Examine the circuit and see why this is so. Socket 1 Socke The ESB maintains a national network of high tension power Fuse or mcb L Live lines. The voltages on these lines are as high as 400 kV. Such voltages are not delivered to domestic premises. Instead the Two-way switch Fuse or mcb L Live voltage is stepped down at transformers to a more suitable Biographical Notes Examination Questions N Neutral E Earth NNeutral lower value. A two-wire cable is used to bring electricity to Fig. Alessandro Volta 2004 Higher Level the home. The neutral is connected to a metal plate in the ground, and so is at 0V. Therefore, the neutral is said to be antwo Italian physist famous as a pioneer in electricity. He was professor of Read the following passage and answer the following questions. Fig.3 Lighting circut, two-way switches Other circuits earthed. The voltage on the live wire alternates to 311V above physics at the Royal School in Como and then at the University of Pavia. He Your home is supplied with at 230 50 Hertz. and below this 50 times a electricity second giving anvolts, effective 220V.At the electrical of domestic load use larg Lighting circuits do invented not require the largeelectrophorus currents. Typically, circuitan breaker in a1775, instrumentOther that types produced charges supply intake aposition is and yourmeter mainare consumer theof 6 amps is used. The conductors in lighting cables therefore independent radial circuits which are not fuse At the house, main fuse installed.unit or fuse board.orAt of static electricity. He also developed the voltaic pile, a type of battery. In The most common are immersion (wat needand not be very thick. One 100 Watt bulb uses less than half an amp as position you will find your main switch. Your sockets, immersion group honour of his work, Napoleon made him a Count in 1810.Cookers and showers require showers. shown below. bathroom heater (or shower) are protected by Residual How is electricity distributed in the house?Current Devices Live L Fuse or mcb (RCD) installed in your fuse board. These provide a high degree of safety IV = Power 0.45 A x 220V = 100 W The cable is then terminated on a consumer unit. From the consumer unit Why use fuses and mcb Georg Simon OhmSocket 2 Socket 1 on these circuits and it is important that they are tested at least every 3 different circuits are run to the various points where electricity is needed A fuse is a wire that will get hot and mel Neutralprotect a circuit feeding more than N safely months. The final circuits are protected byfedMiniature Circuit Therefore, a 6 amp was mcb could - lights, sockets, cookers etc. These circuits are all with the 220V from Breakers. a German physicist, whilst working as a high school teacher, started rated current. By melting, the fuse disco ten 100 W bulbs. In practice, the lighting circuits for a number of rooms are the consumer unit, so all domestic circuits are in parallel. or mcbhis Lresearch with the recently invented electrochemical invented by and fire Live reducing cell, the risk of overheating It is advisable to contact your local ESB about cheaper night tariffs, these Fuse connected in parallel and supplied through one mcb. It is not convenient The live wire connection to every circuit is fed through a safety device Count Volta. Using of his own creation, Ohm Neutral toNhave all lights fail Italian at the same timeAlessandro so it is common to have two orequipment more could make significant savings to your electricity bill. Storage heaters may Like a fuse, a miniature circuit breaker which cuts off the circuit if the current demanded becomes excessive. This E Earth that the current that flows through a wire is proportional toaits lighting circuits in a determined house. current is too large. It is switch with be to avail of these cheaper canused be a fuse or a miniature circuit breakerrates. (mcb). cross sectional area and inversely proportional to Circuit its length. Thisareisfaster Ohm’s breakers and more pre reset.I The circuit breakers Each plug top contains a small cartridge fuse. Cartridge fuses are supplied law and be written as V = IR where V is voltage, is current and R on is a distribu Power circuits for can appliances (sockets) are called miniature circuit breakers. with a rating of 1A, 2A, 3A, 5A and 13A. A fuse should never be replaced resistance. The term appliance is a general term for any thing powered through a by anything other than a suitable fuse. plug and a flexible cable. The standard plug is designed to carry up to 13 amps, though most appliances need considerably less. Inside the plug (Adapted form ‘Home Safety’, Register of Electrical Contractors of Ireland. RECI) Marie there is a fuse. The Andre fuse is usually either aAmpere 3-amp fuse (for appliances up to 660 Watts) or a 13-amp fuse (for appliances up to almost 3 kilowatts). What is a residual curre One device that reduces the likelihood of h Electricity enters and leaves a house th (a) Name and give the colour of the wire that should be connected to the a isFrench physicist, is best for defining to measure the flow of Where a 3-amp fuse sufficient it should be used. known A fault then is more a way Normally, the amount of electricity ent fuse in a standard three-pin plug. (7) likely to blow this fuse only, rather than both blow it and tripthe the ampere. mcb current, which was named afteralso him, He also laid the foundation (b) Explain why replacing a fuse with a piece of aluminium foil is dangerous. (7) (c) A table lamp has a power ratingofof 100W. unit What the Fig.1 Image consumer andismeter most suitable fuse for the lamp? (7) The conductors in the circuit are copper and are insulated. The resistance (d) mustSome be low electrical enough that,appliances are supplied with two-pin plugs. is thecurrent, earth the wire notinrequired in these (7) • atWhy the rated drop voltage between the devices? consumer unit and the load is low (e) Sketch a voltage-time graph of the 230V supply. (7) • the copper does not get too hot. (f) Explain how a Residual Current Device operates. Cables with large diameters have less resistance than(RCD) those with smaller (7) diameters. In general, domestic circuits are classified as lighting circuits Two-way switch Fuse orSocket mcb L Live on the consumer unit. Socket 2 Socket 3 Socket 4 for the1 science of electrodynamics. The RCD consists of a circuit breaker entering and leaving on the live and ne N Neutral E Earth When sockets are fitted as shown below, the circuit is called a radial circuit. mA. Domestic will usually also tri You can find out more about these and other RCDs great (It radiates out from the consumer unit.) Because each socket can supply 63 A, is exceeded. scientists at www.sciencetechnologyaction.com 13 amps there is a limit to the number of sockets that can be supplied by The current for most or all of the circuit one cable. RCD which is between the main fuse and mobile phone chargers need little power. Fig.4 A radial circut with two sockets (g) Givecircuits. one advantage of a Residual Current Device (RCD) or power over a Miniature Circuit Breaker. (MCB) (7) Socket 1 How lighting circuits are heat connected (h) Storage heaters have a large capacity. Why? (7) Two simple lighting circuits are shown below. The first circuit is used where Fuse or mcb L Live Socket 2 L Live N Neutral For further examples there is a single switch, usually at of the past door of paper a room. exam questions check out www.sciencetechnologyaction.com Fuse or mcb same amount leaving. If there is a fault from a live wirewas going to earth Among hiselectricity accomplishments is called a residual or an earth-le In general, almost all the power a house is the converted into of a magnetic figuring outconsumed a way toin measure strength field incurrent relation NNeutral Fuse or mcb L Live heat. Appliances that a lotcurrent, of heat, like electric or kettles,theorem. to generate an electric known asfires Ampere’s Ampere’s law is has a rule A fault current to earth implications. use large currents and consume a lot of power. At 220V, the current per even smaller current, 30 mA, can kill a p that deals with the mutual interaction of current-carrying wires. kilowatt is about 4.5 amps. Many other appliances such as radios or E Earth What is the earth rod? The earth wire in a domestic circuit is co the ground which provides a low-resista the transformer. At the transformer, the the ground. This is why electricity will flo An alternative approach is the ring circuit. Here the circuit takes the form of a ring with both ends of the ring connected to the consumer unit. Both “live” wires are connected to one mcb, both neutrals to the neutral, both earths to earth. This has the advantage that the current demanded can flow two ways and is spread over two conductors. A ring circuit can contain more sockets than you two radial circuits. Can recall the meaning of these Revise the Terms N Neutral Did You Know? Fig.2 Lighting circut, one switch terms? Revising the terminology is a powerful aid for recall and retention. • When the State was founded in 1922, hundreds of small electricity schemes existed. These provided limited electricity supply in cities and towns. Socket 1 Socket 2 Socket 3 Socket 4 Fuse or mcb • There was also a proposal to dam the river Shannon near Limerick and build a hydro-electric electricity station. The government appointed Siemens, a German engineering firm, to provide a detailed scheme for this. The work was started in 1925. Two-way switch Fuse or mcb L Live • This was a giant project and associated with it was a vision of a properly planned and organised electricity supply needed for the development NNeutral of the new State. • Legislation was passed to create the organisation to do this and the ESB was formed in 1927. It gradually took over the major existing suppliers and created an essential national electricity supply body. Socket 1 Socket 2 Transformers; neutral; earthed; live; consumer unit; parallel; fuse; miniature circuit breaker (mcb); insulated; resistance; load; lighting circuits; L Live power circuits; two-way switch; appliance; radial; ring; residual current; earth-leakage current; electrode E Earth N Neutral Check the Glossary of Terms for this lesson at www.sciencetechnologyaction.com