Electrical Installation In Building (politeknik) j3m2q
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ELECTRICAL INSTALLATION IN BUILDINGS
General Objective
C3001 / UNIT 1 / 1
: To understand electrical installation in buildings.
Specific Objectives : At the end of this unit you should be able to : •
differentiate the differences between single and three phase electrical supply
•
compare single and three phase electrical supply
•
understand types of electrical wiring
•
understand equipment in electrical wiring
•
understand and use electrical symbols in buildings
ELECTRICAL INSTALLATION IN BUILDINGS
1.0
C3001 / UNIT 1 / 2
INTRODUCTION The importance of a good, safe residential wiring job is sometimes taken too
lightly. Poorly installed wiring can be very hazardous to the owner or renter as well as to his personal property. A good and safe wiring installation will be a source of satisfaction not only to the electrician, but to the owner or renter as well.
Electricity is too often taken as a matter-of-fact item when, in fact, it is one of our most important servants. We use it without giving it a second thought, and we are inclined to completely ignore the wiring installation as long as the lights come on when we push a switch.
Today, nearly everything around and in the home depends on electricity. This includes housekeeping chores, entertainment, hobbies, heating, cooling and the list is endless. The average person spends the major portion of his time in his home. Most of his
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 3
worldly goods are there; his loved ones are there, so every precaution should be taken to ensure that safe and adequate electrical wiring is installed. Planning for the future growth of electrical usage should also be done. This will involve only a small amount of extra money if done during construction, but if the customer should later find the wiring inadequate for his needs, then many dollars will be required to bring it up to date.
This can be seen from the tremendous increase in electrical consumption since 1928, when only one or two branch circuits were adequate. In the home of today, twenty or more circuits are not uncommon. Electrical usage has far exceeded the predictions of the electric utility companies.
Oooo…..Now I know, why electricity is so important in our lives.
ELECTRICAL INSTALLATION IN BUILDINGS
1.1
C3001 / UNIT 1 / 4
Differences Between Single And Three Phase Electrical Supply.
What is a single-phase electric supply? The supply cable to small buildings such as domestic premises is brought into the building through a trench and left in a position near the entrance ready for the installation of meters and fuse gear. If the meter and fuse gear is to be sited on the inside wall a 100 mm diameter duct is required for the cable.
The meter and fuse gear may, however, be sited on the outside wall. A more recent method for the supply intake to a small building has been the use of an external metal meter cabinet read from outside the premises and thus prevents the difficulty of obtaining access to meters when the building is unoccupied.
The Building Research Establishment (BRE) has developed a combined service intake component for use in domestic premises. The unit consists of a precast concrete block which has provision for the entry of electric, water, gas, telephone and television services. If the electric meter and fuses are housed in the same cupboard as the gas meter, a fire-resisting partition should separate the two meters.
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 5
What is a three phase electric supply? Due to the higher electrical load large buildings such as hospitals, factories and office blocks, will require a three phase supply. The loading in some large buildings may be too high for the local low or medium voltage system to provide and a private sub-station must therefore be installed, fed from the high voltage cables from the Electricity Companies’ nearest switching station. Sub-stations are often required for factories and hospitals.
The electrical installation in a large building is similar to a small building, but is divided into sections. There may be one main intake incorporating large fused switches or circuit – breakers, each of which control a feeder cable to subsidiary distribution s. These are smaller version of the main intake and they control distribution boards for each sub-section.
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 6
Three phase electrical power use Three phase electricity is used to run many different types of machines and equipment today. Although single phase electricity is more prevalent today, three phase is still chosen as the power of choice for many different types of applications. It is often chosen because of its smoother more powerful nature which allows machines to last many years longer and perform functions, such as instant reversing, that are not as appropriate to single or two phase. 1. Uses from appliances Three phase power has many uses from appliances such as refrigerators, to welders, transformers, technical applications, ovens, computers and just about anything else you can imagine being powered by electricity. Three phase by its very nature is a much more smooth form of electricity than single phase or two phase power. It is this more consistent electrical power that allows machines that use it to run more efficiently and last many years longer than their relative machines running on the other phases. Some applications are able to work with three phase power in ways that would not work on single phase at all.
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 7
Economic justification Many properties are, for economic reasons, only connected to one of the three phases of utility power available at the nearest distribution transformer. A single phase supply line was the cheaper option when the premises were built. Similarly, large buildings with 3 phase supplied might still have locations where it is uneconomic or inconvenient to run 3 phase wiring. If three-phase equipment is to be used, a simple comparison can be made: compare the cost for providing three-phase supply (e.g. distribution transformer, power lines, monthly line charges) with the price of a single to three-phase converter.
Example of applications Woodworking workshops a.
Metalworking workshops
b.
Vehicle servicing
c.
Farming
d.
Large buildings
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 8
Single phase to three phase conversion (3 phase converters) Installation Install a single-phase industrial wall switch-socket combination. Connect your new converter. Now you have three-phase power for all your electric motor and machine tool requirements. Motor speeds are constant as with a three-phase supply. Starting motors draw high currents. A Booster E will produce these currents in order to maintain output voltages. This will draw high input currents for a short time. On the single phase supply side
it
pays
to
install
heavy
cables.
This
will
minimize
voltage
drop.
Installation instructions and service schematics are provided with each converter. A simple block diagram and circuit schematic is shown below.
Figure 1.1 Single phase to three phase conversion
Figure 1.2 Single phase to three phase conversion
ELECTRICAL INSTALLATION IN BUILDINGS
1.2
C3001 / UNIT 1 / 9
Types of Electrical Wiring
1.2.1 Open Wiring
Figure 1.3 : open wiring
1.2.2 Hidden Wiring
Figure 1.5 : hidden wiring
Figure 1.4 : open wiring
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 10
1.2.3 Conduit Wiring
We have completed our lesson on the types of electrical wiring. The next topic is equipment that are used in electrical wiring. Are you ready? Let’s go.
Figure 1.6 : Conduit Wiring
ELECTRICAL INSTALLATION IN BUILDINGS
1.3
C3001 / UNIT 1 / 11
How An Equipment Is Used In Electrical Wiring
1.3.1 Electrical Circulation A current which may start at zero, increases to reach maximum, falls away to zero, and then increases to an equal but opposite maximum and falls away again to zero.
1.3.2 Electrical Insulation A non-conducting material such as rubber, plastic, porcelain, glass or mica, surrounding or ing a conductor. For example : Copper conduit Copper conduit is more resistant to corrosion than steel conduit and is therefore useful for outdoor use and for burying in concrete when water is liable to gain access to the conduit during installation. It has excellent electrical conductivity and provides good earthlings, while its very high thermal conductivity tends to reduce condensation. The smooth bore of the copper tube permits the wires to be drawn through easily, both initially or after years of service.
Compression, capillary and bronze welded ts may be used, and inspection bends and junction boxes are cast in copper alloy, such as gunmetal. The tube can be bent by a machine or a spring.
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 12
Aluminium conduit Aluminium conduit is a welded aluminium tube which is prepared for ting by driving a pre-threaded steel tube into the end of the conduit. It can be installed with earthing requirements required by the 16th edition of the IEE Wiring Regulations. The system of ting enables the conduit to be used with standard fittings, and the lightness in weight of the tube offers a reduction in transport and installation costs. The steel inserts which have tapered shanks, are knurled so as to ensure mechanical and electrical connections when fitted into the tube.
To prevent corrosion the steel inserts are sheradised. The conduit may be used for practically every type of installation, and in many respects it is equivalent to galvanized steel. As with copper, it has excellent electrical conductivity and provides good earthing, while its very high thermal conductivity tends to reduce condensation.
Aluminium conduit may be buried in the concrete or plaster, provided they remain dry after setting is complete. If the concrete or plaster is expected to remain damp for long periods, the conduit should be wrapped in adhesive PVC tape. The conduit may be easily bent by a machine and like copper has a smooth bore which enables wires to be drawn through easily, both initially or after years of service.
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 13
Plastic conduit PVC is used which may be unplasticised for rigid conduit and plasticised for flexible tubes. The conduit may be obtained as heavy or light gauge and in round or oval sections. Heavy-gauge conduit may be ted by screwed threads and light-gauge conduit by solvent welding. Injection-moulded PVC fittings are used and the range of fittings is wide enough for a conduit installation to be completely plastic and therefore all insulated. To ensure reliable and earthing continuity in an all-plastic installation, it is necessary to use a continuous earth wire.
PVC is generally unaffected by water, acids, oils and soils and can be safely burried in concrete, plaster or lime. It is light in weight, smooth in bore, quick to install and will not ignite. If the conduit is held in a flame for long periods it carbonises, but the carbon created is non-conductive. The coefficient of expansion is high (0.0003 5/°C), and if the conduit is installed in straight runs for lengths in excess of 6 m the use of expansion is recommended. Smaller diameter conduit may be bent cold by mear’s of a bending spring and larger-diameter tube bent by heating and inserting a special rubber core. As plastic tends to 'spring back' it is necessary for the initial bend to be more acute than is finally required and the conduit secured as soon as possible afterwards. It is recommended that the conduit should be used in temperatures between 70 °C and —10 °C.
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 14
1.3.3 Lightening Conductor Every sub-circuit which originates from the lighting distribution fuse board is generally limited to a total load of 1000W and requires 5 A fuses and switches. In large buildings 15 A fuses and wiring are sometimes used, due to the higher total load on the circuit
1.3.4 Earth Circuit A connection with the ground made in such a manner that an immediate and safe discharge of electrical energy is ensured.
1.3.5 Fuse A safety device consisting of a short length of relatively fine wire in a suitable holder. The device is inserted in the live conductor at a suitable point and if the current exceeds the design value, the fuse wire melts and thus prevents damage to the circuit it protects.
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 15
.
1.
List 3 examples that show the application of three phase.electric supply.
2.
What is the difference between single phase and three phase electric supply?
ELECTRICAL INSTALLATION IN BUILDINGS
1. The example is : Woodworking workshops a.
Metalworking workshops
b.
Vehicle servicing
2.
Three-phase electric supply is for large buildings but single-phase supply is for small buildings.
C3001 / UNIT 1 / 16
ELECTRICAL INSTALLATION IN BUILDINGS
1.4
C3001 / UNIT 1 / 17
Graphic manual symbols in electrical installation in buildings.
What is the symbol in electrical installment in buildings?
One-way switch
Two-way switch
ELECTRICAL INSTALLATION IN BUILDINGS
Discharge lamp
Lighting column
Wall lamp
Fuse
General guidelines
C3001 / UNIT 1 / 18
Filament lamp
Pull or pendant switch
Circuit-breaker
Neutral link
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 19
Please follow these general guidelines pertaining to electrical safety: 1.
Turn off power and unplug from the wall before working on electric or electronic circuits, except when absolutely necessary.
2.
Do not use extension cords as a permanent power source.
3.
Do not work on electrical equipment in a wet area or when touching an object that may provide a hazardous earth ground path.
4.
Turn off power and unplug equipment before checking or replacing fuses. Locate and correct the cause of a blown fuse or tripped circuit breaker before replacing the fuse or resetting the circuit breaker.
5.
Replace defective cords and plugs. Inspect cabling for defects such as frayed wiring, loose connections, or cracked insulation.
6.
Remove metal jewelry, watches, rings, etc., before working on electrical circuits.
7.
Always check the electrical ratings of equipment you use and be sure you use that equipment within its ratings.
8.
Never overload circuits.
9.
Never leave unprotected systems unattended
10.
Never place containers of liquid on electrical systems.
11.
Never defeat the purpose of a fuse or circuit breaker.
ELECTRICAL INSTALLATION IN BUILDINGS
12.
C3001 / UNIT 1 / 20
Never install a fuse of higher amperage rating than that specially listed for your circuit.
13.
Make sure equipment chassis or cabinets are grounded. Never cut off or defeat the ground connection on a plug.
14.
Safely discharge capacitors in equipment before working on the circuits.
If you don’t want to be like this, make sure questions regarding operation, maintenance, or
safety
of
electrical
or
electronic
equipment should be directed to your lab supervisor or an appropriate electronics expert.
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 21
1.
List 5 general guidelines for electrical safety.
2.
Sketch the symbol of a discharge lamp
ELECTRICAL INSTALLATION IN BUILDINGS
1. The guidelines are : a. Never leave unprotected systems unattended b. Never place containers of liquid on electrical systems. c. Never defeat the purpose of a fuse or circuit breaker. d.
Do not use extension cords as a permanent power source.
e. Never overload circuits 2.
C3001 / UNIT 1 / 22
ELECTRICAL INSTALLATION IN BUILDINGS
1.
C3001 / UNIT 1 / 23
Electrical supply in large buildings should be : a) Single phase b) Three phase
2.
Give 1 reason why we need electricity ?
3.
The graphic symbols below are used for:
a.
b.
……………………….. 4.
……………………….
Complete the sentences : a. ……………and …………before working on electric or electronic circuits. b.
Do not use………… as a permanent power source.
c. Remove……………….. before working on electrical circuits. d. Do not work on electrical equipment in a………or…………….. an object that may provide a hazardous earth ground path. e. Always check the………………. of equipment you use and be sure you use
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 24
1. Three phase is better to use for electrical supply in large building. 2. Electricity is important because it is a part of our common necessity. 3. a. wall lamp b. 4
Fuse
The sentences is : a.
Turn off power and unplug from the wall before working on electric or electronic circuits.
b.
Do not use extension cords as a permanent power source.
c.
Remove metal jewelry, watches, rings before working on electrical circuits.
d.
Do not work on electrical equipment in a wet area or when touching an object that may provide a hazardous earth ground path.
e.
Always check the electrical ratings of equipment you use and be sure you use that equipment within its ratings.
1.
General Objective
C3001 / UNIT 1 / 1
: To understand electrical installation in buildings.
Specific Objectives : At the end of this unit you should be able to : •
differentiate the differences between single and three phase electrical supply
•
compare single and three phase electrical supply
•
understand types of electrical wiring
•
understand equipment in electrical wiring
•
understand and use electrical symbols in buildings
ELECTRICAL INSTALLATION IN BUILDINGS
1.0
C3001 / UNIT 1 / 2
INTRODUCTION The importance of a good, safe residential wiring job is sometimes taken too
lightly. Poorly installed wiring can be very hazardous to the owner or renter as well as to his personal property. A good and safe wiring installation will be a source of satisfaction not only to the electrician, but to the owner or renter as well.
Electricity is too often taken as a matter-of-fact item when, in fact, it is one of our most important servants. We use it without giving it a second thought, and we are inclined to completely ignore the wiring installation as long as the lights come on when we push a switch.
Today, nearly everything around and in the home depends on electricity. This includes housekeeping chores, entertainment, hobbies, heating, cooling and the list is endless. The average person spends the major portion of his time in his home. Most of his
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 3
worldly goods are there; his loved ones are there, so every precaution should be taken to ensure that safe and adequate electrical wiring is installed. Planning for the future growth of electrical usage should also be done. This will involve only a small amount of extra money if done during construction, but if the customer should later find the wiring inadequate for his needs, then many dollars will be required to bring it up to date.
This can be seen from the tremendous increase in electrical consumption since 1928, when only one or two branch circuits were adequate. In the home of today, twenty or more circuits are not uncommon. Electrical usage has far exceeded the predictions of the electric utility companies.
Oooo…..Now I know, why electricity is so important in our lives.
ELECTRICAL INSTALLATION IN BUILDINGS
1.1
C3001 / UNIT 1 / 4
Differences Between Single And Three Phase Electrical Supply.
What is a single-phase electric supply? The supply cable to small buildings such as domestic premises is brought into the building through a trench and left in a position near the entrance ready for the installation of meters and fuse gear. If the meter and fuse gear is to be sited on the inside wall a 100 mm diameter duct is required for the cable.
The meter and fuse gear may, however, be sited on the outside wall. A more recent method for the supply intake to a small building has been the use of an external metal meter cabinet read from outside the premises and thus prevents the difficulty of obtaining access to meters when the building is unoccupied.
The Building Research Establishment (BRE) has developed a combined service intake component for use in domestic premises. The unit consists of a precast concrete block which has provision for the entry of electric, water, gas, telephone and television services. If the electric meter and fuses are housed in the same cupboard as the gas meter, a fire-resisting partition should separate the two meters.
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 5
What is a three phase electric supply? Due to the higher electrical load large buildings such as hospitals, factories and office blocks, will require a three phase supply. The loading in some large buildings may be too high for the local low or medium voltage system to provide and a private sub-station must therefore be installed, fed from the high voltage cables from the Electricity Companies’ nearest switching station. Sub-stations are often required for factories and hospitals.
The electrical installation in a large building is similar to a small building, but is divided into sections. There may be one main intake incorporating large fused switches or circuit – breakers, each of which control a feeder cable to subsidiary distribution s. These are smaller version of the main intake and they control distribution boards for each sub-section.
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 6
Three phase electrical power use Three phase electricity is used to run many different types of machines and equipment today. Although single phase electricity is more prevalent today, three phase is still chosen as the power of choice for many different types of applications. It is often chosen because of its smoother more powerful nature which allows machines to last many years longer and perform functions, such as instant reversing, that are not as appropriate to single or two phase. 1. Uses from appliances Three phase power has many uses from appliances such as refrigerators, to welders, transformers, technical applications, ovens, computers and just about anything else you can imagine being powered by electricity. Three phase by its very nature is a much more smooth form of electricity than single phase or two phase power. It is this more consistent electrical power that allows machines that use it to run more efficiently and last many years longer than their relative machines running on the other phases. Some applications are able to work with three phase power in ways that would not work on single phase at all.
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 7
Economic justification Many properties are, for economic reasons, only connected to one of the three phases of utility power available at the nearest distribution transformer. A single phase supply line was the cheaper option when the premises were built. Similarly, large buildings with 3 phase supplied might still have locations where it is uneconomic or inconvenient to run 3 phase wiring. If three-phase equipment is to be used, a simple comparison can be made: compare the cost for providing three-phase supply (e.g. distribution transformer, power lines, monthly line charges) with the price of a single to three-phase converter.
Example of applications Woodworking workshops a.
Metalworking workshops
b.
Vehicle servicing
c.
Farming
d.
Large buildings
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 8
Single phase to three phase conversion (3 phase converters) Installation Install a single-phase industrial wall switch-socket combination. Connect your new converter. Now you have three-phase power for all your electric motor and machine tool requirements. Motor speeds are constant as with a three-phase supply. Starting motors draw high currents. A Booster E will produce these currents in order to maintain output voltages. This will draw high input currents for a short time. On the single phase supply side
it
pays
to
install
heavy
cables.
This
will
minimize
voltage
drop.
Installation instructions and service schematics are provided with each converter. A simple block diagram and circuit schematic is shown below.
Figure 1.1 Single phase to three phase conversion
Figure 1.2 Single phase to three phase conversion
ELECTRICAL INSTALLATION IN BUILDINGS
1.2
C3001 / UNIT 1 / 9
Types of Electrical Wiring
1.2.1 Open Wiring
Figure 1.3 : open wiring
1.2.2 Hidden Wiring
Figure 1.5 : hidden wiring
Figure 1.4 : open wiring
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 10
1.2.3 Conduit Wiring
We have completed our lesson on the types of electrical wiring. The next topic is equipment that are used in electrical wiring. Are you ready? Let’s go.
Figure 1.6 : Conduit Wiring
ELECTRICAL INSTALLATION IN BUILDINGS
1.3
C3001 / UNIT 1 / 11
How An Equipment Is Used In Electrical Wiring
1.3.1 Electrical Circulation A current which may start at zero, increases to reach maximum, falls away to zero, and then increases to an equal but opposite maximum and falls away again to zero.
1.3.2 Electrical Insulation A non-conducting material such as rubber, plastic, porcelain, glass or mica, surrounding or ing a conductor. For example : Copper conduit Copper conduit is more resistant to corrosion than steel conduit and is therefore useful for outdoor use and for burying in concrete when water is liable to gain access to the conduit during installation. It has excellent electrical conductivity and provides good earthlings, while its very high thermal conductivity tends to reduce condensation. The smooth bore of the copper tube permits the wires to be drawn through easily, both initially or after years of service.
Compression, capillary and bronze welded ts may be used, and inspection bends and junction boxes are cast in copper alloy, such as gunmetal. The tube can be bent by a machine or a spring.
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 12
Aluminium conduit Aluminium conduit is a welded aluminium tube which is prepared for ting by driving a pre-threaded steel tube into the end of the conduit. It can be installed with earthing requirements required by the 16th edition of the IEE Wiring Regulations. The system of ting enables the conduit to be used with standard fittings, and the lightness in weight of the tube offers a reduction in transport and installation costs. The steel inserts which have tapered shanks, are knurled so as to ensure mechanical and electrical connections when fitted into the tube.
To prevent corrosion the steel inserts are sheradised. The conduit may be used for practically every type of installation, and in many respects it is equivalent to galvanized steel. As with copper, it has excellent electrical conductivity and provides good earthing, while its very high thermal conductivity tends to reduce condensation.
Aluminium conduit may be buried in the concrete or plaster, provided they remain dry after setting is complete. If the concrete or plaster is expected to remain damp for long periods, the conduit should be wrapped in adhesive PVC tape. The conduit may be easily bent by a machine and like copper has a smooth bore which enables wires to be drawn through easily, both initially or after years of service.
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 13
Plastic conduit PVC is used which may be unplasticised for rigid conduit and plasticised for flexible tubes. The conduit may be obtained as heavy or light gauge and in round or oval sections. Heavy-gauge conduit may be ted by screwed threads and light-gauge conduit by solvent welding. Injection-moulded PVC fittings are used and the range of fittings is wide enough for a conduit installation to be completely plastic and therefore all insulated. To ensure reliable and earthing continuity in an all-plastic installation, it is necessary to use a continuous earth wire.
PVC is generally unaffected by water, acids, oils and soils and can be safely burried in concrete, plaster or lime. It is light in weight, smooth in bore, quick to install and will not ignite. If the conduit is held in a flame for long periods it carbonises, but the carbon created is non-conductive. The coefficient of expansion is high (0.0003 5/°C), and if the conduit is installed in straight runs for lengths in excess of 6 m the use of expansion is recommended. Smaller diameter conduit may be bent cold by mear’s of a bending spring and larger-diameter tube bent by heating and inserting a special rubber core. As plastic tends to 'spring back' it is necessary for the initial bend to be more acute than is finally required and the conduit secured as soon as possible afterwards. It is recommended that the conduit should be used in temperatures between 70 °C and —10 °C.
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 14
1.3.3 Lightening Conductor Every sub-circuit which originates from the lighting distribution fuse board is generally limited to a total load of 1000W and requires 5 A fuses and switches. In large buildings 15 A fuses and wiring are sometimes used, due to the higher total load on the circuit
1.3.4 Earth Circuit A connection with the ground made in such a manner that an immediate and safe discharge of electrical energy is ensured.
1.3.5 Fuse A safety device consisting of a short length of relatively fine wire in a suitable holder. The device is inserted in the live conductor at a suitable point and if the current exceeds the design value, the fuse wire melts and thus prevents damage to the circuit it protects.
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 15
.
1.
List 3 examples that show the application of three phase.electric supply.
2.
What is the difference between single phase and three phase electric supply?
ELECTRICAL INSTALLATION IN BUILDINGS
1. The example is : Woodworking workshops a.
Metalworking workshops
b.
Vehicle servicing
2.
Three-phase electric supply is for large buildings but single-phase supply is for small buildings.
C3001 / UNIT 1 / 16
ELECTRICAL INSTALLATION IN BUILDINGS
1.4
C3001 / UNIT 1 / 17
Graphic manual symbols in electrical installation in buildings.
What is the symbol in electrical installment in buildings?
One-way switch
Two-way switch
ELECTRICAL INSTALLATION IN BUILDINGS
Discharge lamp
Lighting column
Wall lamp
Fuse
General guidelines
C3001 / UNIT 1 / 18
Filament lamp
Pull or pendant switch
Circuit-breaker
Neutral link
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 19
Please follow these general guidelines pertaining to electrical safety: 1.
Turn off power and unplug from the wall before working on electric or electronic circuits, except when absolutely necessary.
2.
Do not use extension cords as a permanent power source.
3.
Do not work on electrical equipment in a wet area or when touching an object that may provide a hazardous earth ground path.
4.
Turn off power and unplug equipment before checking or replacing fuses. Locate and correct the cause of a blown fuse or tripped circuit breaker before replacing the fuse or resetting the circuit breaker.
5.
Replace defective cords and plugs. Inspect cabling for defects such as frayed wiring, loose connections, or cracked insulation.
6.
Remove metal jewelry, watches, rings, etc., before working on electrical circuits.
7.
Always check the electrical ratings of equipment you use and be sure you use that equipment within its ratings.
8.
Never overload circuits.
9.
Never leave unprotected systems unattended
10.
Never place containers of liquid on electrical systems.
11.
Never defeat the purpose of a fuse or circuit breaker.
ELECTRICAL INSTALLATION IN BUILDINGS
12.
C3001 / UNIT 1 / 20
Never install a fuse of higher amperage rating than that specially listed for your circuit.
13.
Make sure equipment chassis or cabinets are grounded. Never cut off or defeat the ground connection on a plug.
14.
Safely discharge capacitors in equipment before working on the circuits.
If you don’t want to be like this, make sure questions regarding operation, maintenance, or
safety
of
electrical
or
electronic
equipment should be directed to your lab supervisor or an appropriate electronics expert.
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 21
1.
List 5 general guidelines for electrical safety.
2.
Sketch the symbol of a discharge lamp
ELECTRICAL INSTALLATION IN BUILDINGS
1. The guidelines are : a. Never leave unprotected systems unattended b. Never place containers of liquid on electrical systems. c. Never defeat the purpose of a fuse or circuit breaker. d.
Do not use extension cords as a permanent power source.
e. Never overload circuits 2.
C3001 / UNIT 1 / 22
ELECTRICAL INSTALLATION IN BUILDINGS
1.
C3001 / UNIT 1 / 23
Electrical supply in large buildings should be : a) Single phase b) Three phase
2.
Give 1 reason why we need electricity ?
3.
The graphic symbols below are used for:
a.
b.
……………………….. 4.
……………………….
Complete the sentences : a. ……………and …………before working on electric or electronic circuits. b.
Do not use………… as a permanent power source.
c. Remove……………….. before working on electrical circuits. d. Do not work on electrical equipment in a………or…………….. an object that may provide a hazardous earth ground path. e. Always check the………………. of equipment you use and be sure you use
ELECTRICAL INSTALLATION IN BUILDINGS
C3001 / UNIT 1 / 24
1. Three phase is better to use for electrical supply in large building. 2. Electricity is important because it is a part of our common necessity. 3. a. wall lamp b. 4
Fuse
The sentences is : a.
Turn off power and unplug from the wall before working on electric or electronic circuits.
b.
Do not use extension cords as a permanent power source.
c.
Remove metal jewelry, watches, rings before working on electrical circuits.
d.
Do not work on electrical equipment in a wet area or when touching an object that may provide a hazardous earth ground path.
e.
Always check the electrical ratings of equipment you use and be sure you use that equipment within its ratings.
1.
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