Questions and Answers
PVC conduit has the mechanical strength of a steel conduit.
False
What must be used instead of PVC conduit as a circuit protective conductor (CPC)?
A separate earth conductor
Flexible conduit provides a continuous earth path.
False
What is a trunking?
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Trunking is more accessible than traditional conduit systems.
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Which of the following materials can trunking be made from?
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Mini-trunking has a cross-section of ____.
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What type of circuit is known for feeding socket outlet units?
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The ring circuit must have its conductors looped into every socket outlet or joint box.
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What is the purpose of a separate CPC in flexible conduits?
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What is the standard width range of cable trays?
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What are components represented in symbols used for in electrical drawings?
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What does a single-line diagram typically show?
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What is the cable size for the load described as 2 nos. 40W filament lamps in a single-line diagram?
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The __________ are the incoming cables providing supply to the installation.
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What is an ELCB?
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What are the three types of conduit used in electrical installation work?
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True or False: A conduit must contain only phase conductors.
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What must be maintained when conduits run into a distribution fuse board?
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What is the function of a bending machine in electrical installations?
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PVC conduit is not suitable for installations subjected to temperatures below _______°C.
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True or False: Installing PVC conduit is slower compared to steel conduit.
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Which of the following are subsidiaries of Singapore Power Ltd? (Select all that apply)
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What is the maximum load for a single-phase supply at 230V?
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What is classified as 'High Voltage' in electrical systems?
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What is the nominal voltage of a low-voltage system in Singapore?
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A three-phase, four-wire AC system has a voltage of 230V between any phase conductor and the neutral.
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What are the two types of liquid-filled transformers mentioned?
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Electricity is generated in power stations, usually located far from the ______.
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What is the main function of a distribution system?
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Match the following voltage levels with their respective types:
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What voltage variation is typically maintained at the supply point?
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Which of the following types of cables are used in low-voltage (LV) systems? (Select all that apply)
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Study Notes
Electrical Services Overview
- Comprises power supply systems, electrical drawings, and wiring installations.
- Singapore Power Ltd operates through subsidiaries: SP Services Ltd (SPSL), SP PowerAssets Ltd (SPPA), and SP PowerGrid Ltd (SPPG).
Singapore Power Ltd Subsidiaries
-
SP Services Ltd (SPSL)
- Facilitates service connections and manages electricity market service requests.
- Handles customer billing, security deposits, and transmission charges.
-
SP PowerAssets Ltd (SPPA)
- Serves as the Transmission Licensee and owns the transmission/distribution network.
-
SP PowerGrid Ltd (SPPG)
- Develops, operates, and maintains transmission and distribution facilities.
Power Supply Modes
- Power supply mode is influenced by building load capacity and location relative to the supply network.
- Supply voltages in Singapore vary:
- 230V, 50Hz (single-phase, max 23kVA)
- 400V, 50Hz (3-phase, up to 2000 kVA)
- 22kV (for contracted capacities from 1,700 kW to 25,500 kW)
- 66kV (minimum contracted capacity of 25,500 kW)
- 230kV (minimum contracted capacity of 85,000 kW)
- Voltage variations at supply points maintained within ±6% of nominal.
Power System Classifications
- High Voltage: >1000V AC, >1500V DC.
- Low Voltage: 50-1000V AC, 120-1500V DC.
- Extra Low Voltage: <50V AC, <120V DC.
- Segregated ELV systems: SELV and PELV are specific low voltage designations.
Low-Voltage Systems
- Defined as distribution voltages below 1000V (typical values: 240V, 400V).
- In Singapore, LV refers to a 400V three-phase four-wire system.
- Consumers over 22kV or 6.6kV must design/install their own high voltage (HT) and low voltage (LV) systems.
High Voltage Consumer Requirements
- Consumers are responsible for supplying, installing, and maintaining their high voltage equipment.
Power Generation Overview
- Predominantly conducted via thermal power stations using steam turbines.
- Steam is produced in high-pressure boilers with fuels like fuel oil and gas.
- Thermal generation includes:
- Steam formation in the boiler.
- Power generation in the turbine room.
Power Transmission Insights
- Electricity transmitted from remote power stations to substations near consumers.
- High voltage (above 22kV) transmission promotes efficiency, higher demand capacity, and reduces losses.
Power Distribution Essentials
- Receives bulk power and delivers to consumers at various voltages.
- Common voltages for distribution: 3.3kV, 6.6kV, 11kV, 22kV, 33kV.
- In Singapore, primary distribution uses 22kV and 6.6kV, stepping down to 400V for use.
Electrical Drawings
- Types include block diagrams, schematic diagrams, and single-line diagrams.
- Block Diagram: General representation of system components.
- Schematic Diagram: Shows electrical connections and circuit configurations.
- Single-Line Diagram: Simplified representation to show power supplies, loads, and components.
Single-Line Diagram/Schematic Distinctions
- Single-line diagrams use symbols to represent components in a straightforward manner, optimizing space.
- Examples include main distribution boards, sub-circuits, and types of protective devices.
Transformations and Cables
- Two transformer types:
- Mineral oil-filled
- Silicon oil-filled
- Typical cables used:
- PVC cables for voltages up to 1000V.
- Armoured and non-armoured XLPE cables for various sizes and ratings.
Summary of Key Points
- Singapore's electrical system is efficient, centrally managed, and relies on structured power supply paradigms with specific consumer responsibilities and technical standards for installations and maintenance.### Electrical Drawings and Single-Line Diagrams
- Single-Line Diagram visually represents electrical installations, often depicting power supply at 400V.
- kVA: Kilovolt Ampere, a unit of measurement for electrical power.
- MCB: Miniature Circuit Breaker, e.g., 60A TPN MCB with a short circuit breaking capacity of 15kA.
- KWH: Kilowatt Hour meter used for measuring energy consumption.
- ELCB: Earth Leakage Circuit Breaker, e.g., 63A 4P ELCB with a tripping current of 30mA.
- Cable specifications: 4x25mm² PVC insulated cables plus 16mm² Circuit Protective Conductor, typically installed in trunking.
Circuit Identifications
- Mains: The incoming cable supplying electricity to installations.
- Main Distribution Board: Central point for connecting the incoming supply and other distribution boards.
-
Submains and Final Circuits:
- Submains: Outgoing cables from the distribution board providing supply to additional boards.
- Final circuits: Outgoing cables from the distribution board supplying specific electrical equipment.
Lighting and Power Load Density
- Various areas have specific lighting and equipment load densities measured in W/m².
- Examples include:
- Shops: 25 W/m² (lighting), 80 W/m² (equipment)
- Restaurants: 35 W/m² (lighting), 80 W/m² (equipment)
- Offices: 15 W/m² (lighting), 20 W/m² (equipment)
Electrical Load Calculation
- Detailed calculations for various rooms in a building, considering floor area, unit loading, and factors for tenant demand.
- Sums for total electrical demand in kW and A, with total calculated demands affecting system sizing.
Wiring Systems
- Wiring system components include conductors, insulation, and mechanical protection accessories for circuit installation.
- Conduit Installations: Pipes or tubes for protecting and routing insulated conductors; offer flexibility in rewiring.
- Types of conduits: Steel, PVC, flexible.
Steel Conduit
- Preferred for durability; comes in various forms, including heavy gauge and solid drawn.
- Can be threaded for fittings, requiring careful installation for electrical continuity.
PVC Conduit
- Lightweight, non-corrosive, and easy to install but lacks the mechanical strength of steel.
- Requires expansion couplings for temperature variation to prevent distortion.
Flexible Conduit
- Composed of metal spirals; prevents torsional stresses on conductors.
- Commonly used in applications where vibration is present, such as motors.
Trunking Installations
- Serves as an enclosure for cable protection, often a more accessible alternative to conduit systems.
- Available in various dimensions and materials; facilitates easy alterations and extensions.
- Features multi-compartment designs to segregate electrical services.
General Installation Best Practices
- Wiring should be completed before the cables are drawn into conduits.
- All conduit connections must be secure to maintain electrical integrity and prevent moisture accumulation.
- Plumbing and electrical installations must be separated to prevent interference.### Metallic Trunking
- Metallic trunking is constructed from mild steel, finished with grey/silver enamel or hot-dipped galvanized coating for moisture resistance.
- Accessories include bends (45° and 90°), tees, and four-way junctions for on-site assembly; fabricated bends may be used for non-standard angles.
- Support trunking while fabricating bends with wooden blocks to prevent deformation; ensure fishplates are riveted or bolted for secure connections.
- Earth continuity at joints is crucial, achieved by tightening fixing screws or installing a copper strip between trunking components.
- If earth continuity tests fail, install an insulated circuit protective conductor (CPC) inside the trunking.
Non-Metallic Trunking
- Available in high-impact PVC; accessories secured with PVC solvent adhesive, offering easy installation and non-corrosive properties.
- Non-metallic trunking requires more frequent fixings due to less rigidity compared to metallic alternatives.
Mini-Trunking
- Mini-trunking is a compact PVC option, suitable for surface wiring in domestic and commercial environments.
- Common cross-sections include 16mm x 16mm, 25mm x 16mm, 38mm x 16mm, or 3mm x 25mm, ideal for switch drops or auxiliary circuits.
Skirting Trunking
- Skirting trunking is made from PVC or steel, resembling skirting boards, and is commonly used in commercial spaces for housing wiring for outlets and telephone points.
Cable Tray Installations
- Cable trays are sheet-steel channels, typically hot-dipped galvanized or PVC-coated, used for supporting MI and SWA cables in industrial settings.
- Adequate support and secure bolting of trays are necessary to avoid cable damage; standard widths range from 50mm to 900mm, with various bends and reducers available.
Lighting Circuits
- Domestic lighting circuits commonly run from a 5A or 6A supply, while larger installations may use 15A or 16A protective devices, primarily utilizing fluorescent and filament lamps.
- A one-way lighting circuit controls one or two lamps through a single switch, connected to the live side of the supply.
- Two-way switching allows control from two locations, with switches needing connection to the live supply.
- Installations typically consist of at least two lighting circuits for reliability during circuit failure, wired with 1.0mm² or 1.5mm² cables, often using loop-in methods.
Power Circuits
- Power circuits for socket-outlets include radial and ring circuits. Socket-outlets are prohibited in bathrooms except for shaver units.
- Radial circuits connect each outlet sequentially and are generally fed from a 20A distribution, while suitable for areas up to 20m² or 50m² with a higher rating.
- Ring circuits entail a loop back to the supply source, typically derived from 30A or 32A, allowing multiple outlets without exceeding 100m².
Electrical Connection Components
- Equipment includes one gang one-way switches and switch-socket outlet (SSO) combinations, ensuring efficient electrical installations.
Drawings and Diagrams
- Students are tasked with creating lighting point layouts for specific areas, along with single line and wiring diagrams based on provided plans.
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Description
Test your knowledge on key concepts of electrical systems in building science. This quiz covers topics like power supply systems, electrical drawings, wiring systems, and installations. Understand the role of Singapore Power Ltd and its subsidiaries in providing electrical services.
