- human body can only withstand a small current of about 50mA.
- larger amt of current → can cause burns / damage to tissue or organs.
- electric current flowing through our bodies can cause involuntary contractions of muscles Reflex Action (Involuntary Actions), such as heart/lung muscles → can lead to death.
Damaged Insulation
- most common
Wires are usually covered with insulating materials to prevent electric shocks. → insulation can be damaged with age and prolonged use.
- Aging of insulation → can occur due to stresses → such as high electric field (due to voltage supply) + temperature.
- when insulators age → they become brittle → break apart → exposing live wires underneath.
- in some buildings → insulation may become damaged as a result of being gnawed by rats.
regardless of cause → exposed live wires can cause electric shocks when touched.
Overheating of Cables
- can be prevented* Overheating → caused by rising temperatures → in electric circuit. We have learnt that energy can be transferred electrically to the internal store of devices →
Overheating occurs when:
- electrical cable passes current that exceeds the limits
- large current flows through wires due to too many plugs being connected to a socket (overloading)
- contact between plug and socket is poor
first 2 scenarios → too much current is drawn.
- leads to overloading. since → amount of energy transferred to internal store increases rapidly with the current.
- hence overloading can cause overheating.
Overheated circuit > can cause fire + explosions as well.
Damp Env.
- common misconception: water and electricity should not come into contact due to risk of electrocution.
- in fact → pure water does not conduct electricity.
- however water from taps / other sources → usually contain charged ions and impurities → that make it a good COE.
- note: this is why swimming poles close when there is possibility of thunder strikes
common to find hair dryers / sockets → for electric shavers in toilets of hote
- poor env. safety design → many electrical accidents occur in damp env.
- hair dryer can cause electric shock if water gets into hair dryer or if there is damaged insulation.
→ do not leave hair dryer on wet sink or use one with wet hands
in addition to keeping hands dry when using electrical appliances, we can protect ourselves from electric shocks by:
- wearing rubber shoes → esp. when carrying out electrical repairs / inspection of electrical faults.
- electric shocks occurs when individual is part of electric circuit and the ground.
- rubber shes act as insulators to cut off closed path to ground → thus keeping us safe.