5.2.1.1 Basic Concepts
The basic mode of generating Electricity for various requirements of mankind today are numerous. Electrical Power Generation methods can be from Thermal, Hydropower, Nuclear, Solar, Wind Power or some other form.
The generated power is distributed through an Electrical Distribution System. To be able to access this Electricity, Consumers need Electrical Installations to achieve his requirements for Lighting, Heating and Air Conditioning, running all types of Electrical Equipment, to name a few.
The following electrical terms are key to the understanding of Electrical Installation:
Current, Voltage and Resistance and their relationship to each other.
Electrical Power and the relationship to the above.
Direct Current, Single Phase, Three Phase and the Neutral.
Real Power, Apparent Power and Reactive Power
Incoming Supply from the Utility and the Consumer Unit.
Electric Cables, Main Switches and MCCB(Moulded Case Circuit Breaker-Rated current up to 1000A) units
Distribution Boards and MCB(Main Circuit Breaker-Rated current not more than 100A) modules.
MCCB MCB
Socket outlets and Switches for power distribution and illumination or lighting.
Electrical Wiring Diagrams and Electrical Load Calculation to commence an Electrical Installation
Single Phase and Three Phase Supply for Alternative or AC Current usage.
Power Factor and Improving of Power Factor for large Electrical Installations
5.2.1.2 Current
Current is a flow of electrical charge carriers, usually electrons or electron-deficient atoms. The common symbol is 'I'. The standard unit is ampere 'A',
5.2.1.3 Voltage
Voltage, also called electromotive force, is a quantitative expression of the potential difference in charge between two points in an electrical field.
The greater the voltage, the greater the flow of electrical current (that is, the quantity of charge carriers that pass a fixed point per unit time) through a conducting or semiconducting medium for a given resistance to the flow. Voltage is symbolized by letter V or E. The standard unit is volt (v).
5.2.1.4 Electric Power
Electric Power is the rate of energy consumption in an electrical circuit. The electric power is measured in units of watts.
The Relationship between Current, Voltage and Electric Power.
The electric power in watts associated with a complete electric circuit or a circuit component represents the rate at which energy is converted from the electrical energy of the moving charges to some other form, e.g., heat, mechanical energy, or energy stored in electric fields or magnetic fields. For a resistor in a D.C Circuit the power is given by the product of applied voltage and the electric current:
P=VI
Power = Voltage x Current
watts = volts x amperes
The amount of current in a circuit depends on the amount of voltage available to motivate the electrons, and also the amount of resistance in the circuit to oppose electron flow. Just like voltage, resistance is a quantity relative between two points.
5.2.1.5 Direct Current (DC)
Direct current is an electric current flowing in one direction only.
DC is the unidirectional flow or movement of electric charge carriers (which are usually electrons). The intensity of the current can vary with time, but the general direction of movement stays the same at all times. The term DC is used in reference to voltage whose polarity never reverses.
Direct current is produced by electrochemical and photovoltaic cells and batteries. In contrast, the electricity available from utility mains in most countries is AC (alternating current). Utility AC can be converted to DC by means of a power supply consisting a transformer, a rectifier (which prevents the flow of current from reversing), and a filter (which eliminates current pulsations in the output of the rectifier).
5.2.1.6 Alternating Current (AC)
Alternating Current (AC) is a type of electrical current, in which the direction of the flow of electrons switches back and forth at regular intervals or cycles. Current flowing in power lines and normal household electricity that comes from a wall outlet is alternating current.
One advantage of alternating current is that it is cheap to change the voltage of the current. Furthermore, the inevitable loss of energy that occurs when current is carried over long distances is far smaller with alternating current than with direct current.
Single Phase and Three Phase Supply for Alternative or AC Current usage.
5.2.1.7 Single Phase Power
Single phase power refers to a two wire Alternative Current (AC) power circuit. Typically there is one power wire and one neutral wire. 120V (230V in some countries) is the standard single phase voltage with one 120V power wire and one neutral wire. Power flows between the power wire (through the load) and the neutral wire.
5.2.1.8 Three Phase Power
Three phase power refers to three wire Alternative Current (AC) power circuits. Typically there are three (Phase A, Phase B, Phase C) power wires (120 degrees out of phase with one another) and one neutral wire. The neutral wire is earthed at the switchboard.
Most US commercial buildings use a 3 Phase 4 Wire 208Y/120V power arrangement because of its flexibility. This arrangement provides (3) 120V single phase power circuit and (1) 208V three phase power circuit. 120V power flows (alternating) between any power wire (through the load) and the neutral wire. 208V power flows (alternating) between the three power wire (through the load). Low power loads (lights, computers, etc.) are powered using any 120V single phase power circuit and high power loads (Water Heaters, AC Compressors) are powered using the 208V three phase power circuit.
5.2.1.9 True Power, Apparent Power and Reactive Power
We know that reactive loads such as inductors and capacitors dissipate zero power, yet the fact that they drop voltage and draw current gives the deceptive impression that they actually do dissipate power. This "phantom power" is called reactive power, and it is measured in a unit called Volt-Amps-Reactive (VAR), rather than watts. The mathematical symbol for reactive power is Q.
The actual amount of power being used, or dissipated, in a circuit is called true power, and it is measured in watts (symbolized by P)
The combination of reactive power and true power is called apparent power, and it is the product of a circuit's voltage and current, without reference to phase angle.
Apparent power is measured in the unit of Volt-Amps (VA) and is symbolized by capital letter S.
As a rule:
True power is a function of a circuit's dissipative elements, usually resistances (R).
Reactive power is a function of a circuit's reactance (X).
Apparent power is a function of a circuit's total impedance (Z).
5.2.1.10 Power Factor
Power Factor is equal to the real or true power P in watts (W) divided by the apparent power (S) in volt-ampere (VA):
PF = P(W)/S(VA) or simply put:
Power Factor is the ratio between the kW and the kVA drawn by an electrical load where the kW is the actual load power and kVA is the apparent load power.
5.2.2.1 Consumer Unit (CU)
The Consumer Unit, also called fusebox or main distribution board, contains these things:
-A main isolating switch. This switches off everything.
In most cases at least one:
-RCD(Residual Current Device-a circuit protective device designed to achieve two important result:
To protect users from serious electric shock.
To protect circuit from sustained earth faults that may occur where Fuses, and MCBs(Main Circuit Breakers) does not function correctly because of the earth loop impedance is too high)
-A fuse or MCB for each circuit. This cuts the power to the circuit in the event of high fault current.
-An earth connection block which connects earth to the earth wires of the various circuits.
5.2.2.2 Main Switch
A main switch is a central cut-off switch that controls the smaller cot-off switches and machine of a building.
The main switch can be cut off by a human or a computerized system to control the flow of power in the building.
The main switch, also referred to as a distribution board, divides the feed of electrical power to a building into subsidiary circuits and provides a protective fuse for each circuit. When a circuit is overloaded, the fuse at the main switch is popped. This effectively stops power from flowing through the circuit and prevents fire from the overload.
RCD(residue current device) MCCD(moulded case circuit device) 185px 13A (Double Socket)
5.2.2.3 Split Load CU
A Slit Load CU divides the MCBs into 2 or more separate banks. Each bank usually having its own RCD. There should also be a master switch that will switch the whole CU. The split load CU has the following advantages:
Some wiring work can be carried out with just a section of a CU turned off, perhaps retaining access to light and power while working.
Almost all faults can only take out the power to part of the system
5.2.2.4 Earthing
Earthing is a fundamental safety system used in electrical installations. It works in co-ordination with circuit breakers MCBs, Fuses, and RCDs to ensure that an electrical supply can be disconnected quickly in the event of a fault. This greatly reduces shock risk.
Radial Ring Circuit
A ring main is a wiring ring between a circuit breaker on a consumer unit and the sockets it supplies.
One wire leaves the consumer unit and connects to the first socket, a second cable them leaves this socket and goes to the next, at the last socket in the chain, the last connection goes back to the consumer unit creating a ring.
Steps involved:
Preparing Electrical Layout Drawings and Schematic Drawings based on Architectural Drawings
Determine Electrical Specifications
List out Material and Component requirements
Decide Main Distribution Board locations
Lay conduit or Trunkings in the building as necessary
Install boxes for Switches and Sockets
Install Distribution Boards and Main Switches
Install Cables from Distribution Boards to Switches, Light/Fan points, and Socket outlets
Install Lights Switches, Sockets and other accessories
Test the Installation
Obtain Service Connection from Power Utility Company
Ready for Commissioning of the Electrical Installation.
