Chapter 4: Electricity and Magnetism {Pt 2} Flashcards
What are the most dangerous consequences of using electricity?
Electric shock and electric fire
What is electric shock and electric fire caused by?
Damaged insulation
Overheating of cables
Damp conditions
Excess current
What materiel is used for insulating wires?
Rubber
What does damage of insulation result in?
- Electric shock causing serious injury or even death to users
- Short circuit in the current path by connecting exposed current-carrying conductors together resulting in the wires heating up and fire hazards.
What is overheating of cables caused by?
Short-circuit or overloading of cables are conditions that lead to large currents.
Overheating of cables happens when large currents are made to flow through these conductors, these will heat up and produce very high temperatures.
What does the overheating of cables result in?
Melting of the insulation and catching fire
Why should you not come into contact with electrical appliances if you are wet?
This will result in large currents flowing through the body causing electrical shock and leading to serious injury or even death.
What are the signs of an electrical overload?
Dimming lights
Buzzing outlets or switches
Outlet or switch covers that are warm to the touch
Burning odours from outlets or switches
Scorched plugs or outlets
Power tools, appliances or electronics that seem to lack sufficient power
What does the mains electricity plug contain?
Three wires:
- live
- neutral
- earth
In a plug, the live wire and the neutral wire are the two wires that form the complete circuit with a household appliance.
The earth wire does not normally form part of the circuit and is included as a safety wire.
It is connected to ‘earth’, which is usually a large metal spike buried under a house.
Which wire should the switch always be connected to?
The live wire so that when it is off, no current flows through the appliance.
If they were in the neutral wire, light switches and power sockets would be ‘live’ when the switches were ‘off’ or fuses ‘blown’.
A fatal shock could then be obtained by, for example, touching the element of an electric fire when it was switched off.
What is a fuse?
It is a small, thin conductor designed to melt and separate into two pieces for the purpose of breaking a circuit in the even of excessive current.
How are fuses connected?
Always in series to protect them from overcurrent so that when the fuse blows, it will open the entire circuit and stop current through the components
How are fuses rated?
Primarily in terms of maximum current.
But are also rated in terms of how much voltage drop they will safely withstand after interrupting a circuit
Where is the best place to install a fuse in a grounded power system?
On the ungrounded conductor path to the load.
That way, when the fuse blows, there will only be the grounded (safe) conductor still connected to the load, making it safer for people to be around.
How do you select the correct fuse?
Common fuse sizes: 3A, 5A and 13 A
Once the current is known the next highest fuse rating is chosen.
How is electric power calculated?
Give a suitable fuse rating for
