Chap 3b-Electrical Services: Basic Concepts & Terminology

• Electrical services provide electricity for appliances, machinery, and commercial needs
• Nature of electricity: Energy transported by electrons, converted from other sources

Basic Electrical Concepts and Terminology

• Faraday Effect: Foundation for electromagnetic induction understanding
• Voltage (V): Potential to move charge, measured in volts
• Current (I): Charge movement, measured in amperes (amps)
• Resistance (R): Opposition to current flow, measured in ohms (Ω), Ohm's Law: V = I x R
• Power (P): Rate at which electrical energy is transferred, measured in watts, Formula: P = I x V = I² x R

Electric Circuits Terminology

• Electric Current (I): Flow of electrons from one end of a conductor to another, Unit: Ampere (A), Formula: I = Q/t (Q = Charge in Coulombs, t = time in seconds).
• Ampere: 1 Ampere = 1 Coulomb of charge passing through a point in 1 second
• Potential Difference (Voltage): Work/energy required to move charge in a circuit, Unit: Volt (V), Formula: Voltage = W/Q (Work/Charge)
• Conductors: Materials allowing easy current flow (e.g., metals)
• Insulators: Materials greatly opposing current flow (e.g., glass, paper, Teflon)
• Electromotive Force (EMF): Energy to move charge, measured in volts
• Electrical potential provided by an EMF source within a circuit
• A device supplying electrical energy is considered an EMF source
• Resistance (R): Opposition to electric current flow, Unit: Ohm (Ω)
• Defined as voltage ratio (V) across an object to current (I) through it
• Specific Resistance (Resistivity): Electrical resistance offered by a unit length/cross-section of a material, Formula: P=RA/I
• Conductance (G): Inverse of resistance, ratio of current to voltage, Unit: mho (U) or Siemens (S)
• Conductor: Allows the flow of electrical current in one or more directions (e.g., Metal Wire)
• Semiconductors: Crystalline/amorphous solids with distinct electrical characteristics, between conductors and insulators
• Resistance is higher than conductors but lower than insulators

Direct Current (DC) vs. Alternating Current (AC)

• Direct Current (DC): Constant direction, magnitude may vary, voltage not easily changed, hard to transmit long distances
• Sources: Batteries, solar cells, fuel cells, rectifiers (AC to DC converters)
• Alternating Current (AC): Magnitude/direction change over time, voltage easily changed by transformers, transmitted long distances
• Sources: Power plants (hydroelectric/thermal), generators, inverters (DC to AC converters)

Technical Terms Related to Wiring

• Domestic Electric Supply: Single Phase - 240V at 50 Hz (Live/Red, Neutral/Black), Three Phase - 420/240V at 50 Hz (Three Live, one Neutral)
• Fuse: Thin, low melting point wire protects from heavy current ("cut out")

Types of Fuses

• Rewirable: Common, uses porcelain base, connect to Live Phase, lead/tinned copper/aluminum/tin-lead alloy
• Cartridge: Totally enclosed container with metal contacts
• Miniature Circuit Breaker (MCB): Breaks circuit during excess current, rated current ≤100 A, thermal or thermal-magnetic operation

Advantages of MCBs over Fuses

• Automatically switches off during overload/fault, more sensitive, quick restoration (no rewiring), safer

• Earth Leakage Circuit Breaker (ELCB): Breaks circuit upon current leakage

• ELCB Types: Voltage and Current

• ELCB Characteristics: Phase, Neutral, & Earth wire connected through it, based on Earth leakage current

• ELCB Operating Time: Quick operation (e.g., 0.65 msec) to prevent electric shock, safe limit for human body is 30mA

• Residual Current Circuit Breaker (RCCB): Breaks circuit on current imbalance in live and neutral wires (leakage)

• Cables: Used to connect devices for electrical signals/power transferring

• Earthing: Protects from electrical shock by enabling fault current to flow to earth

Additional Protective Measures

• Prevent dangerous potential of exposed parts, provides fault current alternative path, protects buildings/machinery/appliances
• Types: Wire, Rod, Pipe, Plate earthing
• Conventional Earthing: GL pipe/copper plate surrounded by charcoal/salt layers, water pouring requires
• Wire Earthing: Copper wire in trench (rocky terrains)
• Rod Earthing: GI rod (20 mm diameter) buried (200-300 cm)
• Pipe Earthing: Pipe as earth electrode, surrounded by charcoal/salt
• Plate Earthing: G.l./copper plate buried, surrounded by charcoal/salt

Electrical Accessories Defined

• Switch: Breaks or diverts an electrical circuit
• Types: One-way (simple on/off), Two-way (control from two locations), Push-Button (simple mechanism), and Pull (chain or string actuated)
• Lamp Holders (Light Bulb Sockets): Provide electrical connections to lamps and support them
• Types (Holding Pattern): Bayonet Cap (BC), Edison, and Goliath; (Mounting Pattern): Batten, Pendant, Angle, or Bracket

Electrical System Components

• Ceiling Roses: Connect lighting fixtures to electrical supply
• Types: Two-Plate, Three-Plate
• Modern ceiling roses have an earth terminal
• Adapter: Supplies power to small instruments.
• Connector: Connects relays/timers with tube lights/fans
• Distribution Board: Connects two or more wiring systems with 15A fuse per circuit
• Socket Outlets: Fixed to switchboards, with Phase [P], Neutral [N], and Earthling [E] terminals
• Plug: Gains power from socket outlets to connect instrument circuits
• Plug Types: Two-pin (brass pins for phase/neutral) or Three-pin (three brass pins, one for neutral)
• Available in 5A and 15A ratings
• Mounting Blocks: Circular/square blocks (wood/PVC), insulated base for ceiling/lamp holders/switches
• Main Switch: Near electric meter, controls building's electrical circuit ("Iron Clad Switch")

Main Switch Types

• Double Pole Iron Clad: Single-phase connections
• Triple Pole Iron Clad: Three-phase connections

Types of Wiring Based on Insulation

• T.R.S.: Modified V.I.R wire with tough rubber sheath for extra insulation/protection, single/two/three conductors
• Weatherproof Wire: Cotton braiding coating waterproof, not in use anymore
• LC: Lead pipe over rubber insulation with conductor coating, good to use for moisture filled conditions
• MICC: Copper conductor coating magnesium oxide, PVC coating, mines/factories/furnaces/boilers/rolling mills
• PVC: PVC-coated copper conductor, resistance to resistance to moisture, vibration, water, heat, oil, and UV light
• Flexible Wires: Multiple thin strands, plastic (PVC) insulated, using for household appliances

Types of Wiring Systems

• Cleat Wiring: Insulated conductors on wooden cleats, used for temporary, easy to install and re used, easy to inspect with easy modifications
• Poor Appearance: Poor Appearance: Poor outlook, requiring occasional cleaning and higher risk of mechanical damage
• Batten Wiring: Uses rubber wires, moisture/chemical protection, only low voltage installation
• Metal Sheathed Wiring: Insulated wires covered by lead-aluminum alloy sheath, provides current path, suitable to provide leakage path
• Casing/Capping Wiring: Insulated conductors inside PVC boxes with wooden strip (capping), indoor installations, requires high flammability
• Condult Wiring: Cables in PVC tubes, can be embedded, used for public constructions

Factors Affecting the Choice of Wiring

• Durability: Meet standards, weather/fumes resistance
• Safety: Prevent leakage, shocks, fire hazards
• Appearance: Enhance interior aesthetics
• Cost: Affordable
• Accessibility: Easy switches/outlets and extra space
• Maintenance Cost: Minimal
• Mechanical Safety: Protected from damage