Electrical Basics
What unit is electrical resistance measured in?
Ohms
Ferrous metals contain what?
Iron
At what temperature is water most dense?
4 degrees C
What size protective device is needed for a 5kW shower on a 230V supply?
21.7Amps (30A breaker)
What is the SI unit for area?
m2
What electrical system has electrons flowing in one direction?
Direct Current (DC)
What property describes a material's ability to be stretched without breaking?
Ductility
What heat transfer method causes the circulation of warm air?
Convection
What size protective device is needed for a 9kW shower on a 230V supply?
39.1Amps (40A breaker)
What colour is the earth insulation on temporary continuity bonding?
Yellow & Green
What type of material allows the free movement of electrons?
Good conductor
What property describes a material being fabricated without fracture?
Malleability
How much does water expand when heated to 90°C?
4%
A 5A protective device is installed on a 230V supply. What is the maximum load allowed?
1.15Kw
A 3 pulley system needs to lift a 900kg load. What force is required to lift the load?
300kg
What overcurrent protection device has an integral test feature?
RCD Residual Current Device
Which pair of metals are most affected by electrolytic corrosion?
Copper & Aluminium / Magnesium
Calculate the energy required to heat 140 litres of water from 4°C to 80°C using a specific heat capacity of 4.186 kJ/kg°C.
44,539.04kJ
A boiler rated at 690W is fitted with a 13A fuse. What action should be taken?
Change to a 3A fuse
A 3m copper pipe is heated from 15°C to 60°C. Calculate the expansion using a coefficient of linear expansion of 0.000017 m/m°C.
2.295mm
Voltage ÷ Resistance = X. What does X represent?
Current
What is a sign that a brass fitting is suffering from dezincification?
White powdery coating
Explain the difference between sensible heat and latent heat.
Latent heat - Change in temp & state
Sensible heat - Change in temp, not state
A 230V immersion heater draws 13A. Calculate its power rating in watts and kilowatts.
2,990 W (2.99kw)
What happens to temporary hard water at 65 degrees C?
Calcium carbonates leave the water to form limescale, this causes a reduction in efficiency.