WIRING SYSTEMThere are 2 types of wiring system;

• Single-phase• Three-phase

This system has mains voltage between live and neutral wires

The frequency of DC voltage is 50 Hz. This system is used in house application It supplies 240 V to power more home

electrical appliances In most cases, an additional safe ground

wire is used to increase user safety.

SINGLE-PHASE SYSTEM

This system is generated by generator that produces three voltage, each has the same frequency.

This system is used in industrial and electrical distribution.

THREE-PHASE SYSTEM

A colour coding has been adopted to standardise the colour schemes in cables and flexible cords.

The international colour code is to be used at international level in wiring system.

INTERNATIONAL COLOUR CODE

Colour Wire

BROWN LIVE

BLUE NEUTRAL

GREEN WITH YELLOW STRIPE EARTH

The international colour code for main wiring is;

A 3-pin plug has 3 terminals connected to 3 types of wires;◦ Terminal L, connected to live wire◦ Terminal N, connected to neutral wire◦ Terminal E, connected to earth wire

WIRING IN 3-PIN PLUG

3pin plug wiring

Live wire supplies current, neutral wire carries current away from electrical appliances, while earth wire earthed leaked current.

3-pin plug contains one fuse connected to the live wire to control current supply.

Fuse will melt and interrupt electricity supply if excess current flows through it.

This is essential to prevent damage to electrical appliances.

Electrical energy is measured in Joules (J) by using energy meter

1 kilojoule (kJ) = 1000 joule (J) Electrical energy used by an electrical

appliance in a given time can be calculated using the following formula;◦ E = Vlt

Where E = amount of electrical enegy used V = voltage in volts I = current in amperes (A) t = time in second (s)

Cost of electrical usage

The power of an electrical appliance is the rate of usage of electrical energy by that appliance.

Power (W) = energy (J) / Time (s) Energy (J) = power (W) x Time (s) ; or Power (W) = voltage (V) x current (A)

1 W = 1 J s-1

the home energy meter measures electrical energy used in kilowatt-hour

1 kilowatt (kW) = 1000 watt (W) 1 kWh is the amount of energy used by 1

kW electrical appliance for 1 hour.◦ 1 kWh = 1000 W x 1 hour

= 1000 W x 3 600 s = 3 600 000 J

Power is measured in watt (W) or joule (J) per second (J s-1)

Cost = power (kW) x time (h) x cost of 1 kWh

Cost of electricity is calculated using the equation below;

A 240 V, 100 W electric kettle needs 15 minutes to boil water in it. What is the electrical energy used by the kettle?

Solution ;◦ power = 100 W◦ Time = 15 x 60 =900 seconds◦ Amount of energy used = power x time ◦ = 100 x 900◦ = 90 000 J = 90 kJ

Example 1;

Serena irons her clothes every week. The iron has 300 W power. If she irons her clothes 4 times in October for half an hour each time, what is the electrical energy used in kWh?

Example 2 ;

On a hot day, Ali switched on a 240 V, 50 W and 240 V, 500 W air conditioner as well as watches a 240 V, 250 W television. He watched a live football match lasted from one to five in the afternoon. What is the electrical energy usage during that period?

Example 3;

At the end of May, the reading of the power meter in Veena’s house is 02597 while the reading at the end of April is 02319. given that the tariff rates for residential houses are RM0.218 for the first 200 units, RM0.258 for the next 800 units, and RM0.278 for the remainder units. How much money will be paid by veena’s family for electrical energy usage in May?

Example 4 ;