Questions and Answers
The allowed voltage drop equals 4 x 240 divided by ______
100
For a 1 mm2 cable, the maximum length or run equals 9.6 x 103 divided by ______ x 44
12.5
The resistance of the protective conductor should not exceed ______ Ohm during testing
1
For 1.5 mm2 cable, the maximum length or run equals 9.6 x 103 divided by ______ x 29
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The tests of effective earthing involve four separate ______
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The line-earth loop impedance test meter is attached to a ______ three-pin plug
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Inspection and testing is carried out before the installation is put into ______
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The operation of electrical installations must be safe, efficient, and in accordance with ______ demands
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Fuses and switches must be fitted into a line ______
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The maximum length for a 2.5 mm2 cable based on the allowed voltage drop is ______ m
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Study Notes
Types of Current
- Alternating Current (A.C.): Fluctuates from zero to maximum, reverses direction, and repeats. Induced in coils of wires by moving magnetic fields.
- Direct Current (D.C.): Flows continuously in one direction, commonly produced by batteries.
Public Distribution of Electricity
- Power for large towns delivered via cables or overhead lines at 132kV or 33kV.
- Heavy industries receive power at 33kV; light industries at 11kV.
- High voltage power is converted to 415/240V for domestic use.
- Economical grid system ensures interconnectivity among power stations for maintenance reliability.
Electricity Supply to Buildings
- Single Phase Supply: Small buildings are usually connected with one phase and neutral. Load must be balanced by connecting buildings sequentially across three lines.
- Three Phase Supply: Applicable for higher power demands.
Power Sockets and Lighting Switches
- Standard socket height: 150-250 mm above floors/work surfaces.
- For buildings catering to the elderly/infirm, socket height: 750-900 mm.
Electricity Generation
- Sources include hydro (flow of water), thermal (steam from oil/coal), wind, solar (photovoltaic), nuclear fission, coal, and natural gas.
Transformers
- Conversions between high and low voltage power require transformers (step-up and step-down).
- Substations manage the conversion and control of electric power.
Transformer Specifications
- Common transformer capacities include 600-1000KVA, 300-500KVA, and 100-200KVA.
Voltage Drop Calculations
- Allowed voltage drop calculation: 4 x 240V / 100 = 9.6V.
- Maximum cable lengths determined for 1mm², 1.5mm², and 2.5mm² cables are 17.5m, 26.5m, and 42.7m respectively.
Testing of Electrical Installations
- Regular inspection and testing ensure safety, efficiency, and compliance.
- Key tests include:
- Verification of Polarity: Checks fuses, switches, plugs, and sockets for correct connections.
- Effective Earthing Tests: Includes tests for protective conductor resistance, with a maximum allowable resistance of 1Ω.
- Earth Loop Impedance: Assesses line-earth impedance with a meter to ensure safety and efficiency.
Conclusion
- Understanding current types, electricity distribution, safety standards, and efficient energy use is essential for electrical installations.
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Description
Explore the different types of electric currents in this quiz. Learn about alternating current (A.C.) and direct current (D.C.), their characteristics, and applications. Ideal for students studying electricity and circuits.
