Practical Electricity Flashcards
Damaged Insulation
if someone touches an exposed piece of wire, they could be subjected to a lethal shock
Overheating of cables
Passing too much current through too small a wire (or leaving a long length of wire tightly coiled) can lead to the wire overheating. This could cause a fire or melt the insulations, exposing live wires
Damp conditions
If moisture comes into contact with live wires, the moisture could conduct electricity either causing a short circuit within a device (which could cause a fire) or posing an electrocution risk
A fuse is a safety device designed to cut off the flow of electricity to an appliance if the current becomes____________
too large (due to a fault or a surge)
Fuses come in a variety of sizes (typically 3A, 5A and 13A) – in order to select the right fuse for the job, you need to know how much current an appliance needs.
The fuse should always have a current rating that is higher than the current needed by the appliance, without being too high – always choose the _____________
next size up
Suppose an appliance uses 3.1 amps
A 3 amp use would be too small – the fuse would blow as soon as the appliance was switched on
A 13 amp fuse would be too large – it would allow an extra 10 amps to pass through the appliance before it finally blew
A 5 amp fuse would be an appropriate choice, as it is the next size up
Many electrical appliances have metal cases
This poses a potential safety hazard.
Suggest How?
If a live wire (inside the appliance) came into contact with the case, the case would become electrified and anyone who touched in would risk electrocution
The earth wire is an additional safety wire that can reduce this risk
Fuse rating of 13A
Double Insulation
Some appliances do not have metal cases and so there is no risk of them becoming electrofied.
Such appliances are said to be double insulated, as they have two layers of insulation:
Insulation around the wires themselves
The non-metallic case acts as a second layer of insulation
Power
is the rate of energy transfer (the amount of energy transferred per second).
The power of an electrical component (or appliance) is given by the equation:
Power = Current x voltage P = I x V
The amount of electrical energy used by a component or appliance depends upon three things:
The current
The voltage
The amount of time the device is used for.
energy transferred = current x voltage x time
E = I x V x t
Domestic consumption of electrical energy is measured by electrical meters units of _______________
kilowatt-hour (kWh)
Each consumed energy unit (kWh) is billed according to a fixed or variable rate. The total cost of energy usage for a defined period is the product of number of consumed energy units in kWh and the charge per energy unit.
Wiring a switch?
Remove a sufficient amount of outer insulation of the three core wires, Live (brown), Neutral (blue) and Earth (green with yellow).
Open the mains plug with a screwdriver and take out the fuse.
Remove about 5 mm of the insulation from three wires and twist the copper strands of each wire together.
Clamp the edge of the removed outer insulation by tightening the two screws that are holding down the outer insulation wire.
Insert each wire to the correct terminal as shown and tighten each screw so that the wires are fixed properly with the terminals.
Fix the fuse back to its position and close the covering of the plug.
circuit breaker
is usually made up of a reusable spring-loaded type of switch. The function of the circuit breaker is similar to that of the fuse. If current exceeds its breaking setting, it will spring open and break the circuit as in a fuse. The device can be reused by resetting the spring-loaded switch.
