Electrocution: Harm caused by an electric current passing through the body
For this to occur, 2 things must happen
Electrical contact: there must be complete non-disrupted electrical contact between you, the source, and the ground (sometimes dual contact with source). This means electricity can flow through your body (from the source) and into the ground/source again and a complete circuit is achieved
Potential Difference: there must be a potential difference between the electrical source and the end point (i.e. the ground). If there is no potential difference between the 2 points of contact, electricity will not flow through your body
Thermal Shock: a type of electrocution where damage is caused by the generation of heat as the electric current bypasses through the body’s resistance
Electric shock: A type of electrocution where damage is caused by the outside electrical currents upsetting and disturbing the small electrical currents in the body, causing damages to organs, and possible heart failure
If a circuit is live, there is current flowing through it
A short circuit is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circuit.
Safety Devices
Devices that prevent electrocution
Prevent electrical leakage or completion of a circuit
short circuit: overflow of current in a system
Fuses
Wires made of extremely low melting point alloys that prevent electrical devices from overloading with current
When a short circuit occurs (because of bare wires touching): the circuit overloads with current (as resistance has decreased), and if the circuit is not disrupted, the high current causes excessive heat dissipation and eventually catches fire (due to friction)
Fuses are specific components of the electrical circuits
When a high current flows through the fuse, the fuse simply melts, disjoining the two wire segments adjacent to the fuse and thus breaking the circuit
RCD - Residual Current Device
A device that breaks a circuit if it detects current leaking from the circuit
The RCD measures the current in the active (live) conductor that conducts electricity to an appliance and a neutral return conductor
If there is an imbalance of current on the active and neutral wires, this indicates current may be leaking through the body of a person in contact with an energised device
Any imbalance of currents (approximately 30 milliamps or more) between the active and neutral conductors causes the RCD to break the circuit within 20 to 24 milliseconds
Double Insulation
Type of insulation around the live/active part of a device (where current is flowing) that physically prevents contact with the energised part fo the device
E.g., plastic covering around the energised motors of a hairdryer
Double insulation is mostly made of well insulated plastics
Circuit Breakers
Automatically operated electrical switches that protect an electrical circuit from damage caused by overloading of circuits (usually caused by short-circuits)
Once a fault is detected, the circuit breaker works like a switch to break the circuit, but unlike a fuse, the circuit breakers can be reset
Earth Wires
An earth wire exists to provide protection against a fault occuring in the appliance. The earth wire is connected to the metal casing of an appliance and the ground
In the case of a live wire coming loose and touching the meal, the entire appliance will become live (current runs through it)
If an earth wire is connected, a short circuit will occur, as the current will pass from the live metal to the wire and to the ground. Thus if a human touched the appliance, current will not flow through them, but directly to the ground
Thus, the earth wire protects the user
Earth wires are commonly used in association with a fuse as due to the short circuit occurring, there will be a current overload leading to the fuse “blowing” and thus the circuit being broken
Dr Waters Definitions
Fuse: excess current will melt wire, break circuit and prevent house fire, but not death by electrocution
Residual circuit devices (rcd): monitors for any difference in current between active and neutral wires, and if difference is detected then circuit is cut (tripped) in nano-seconds
Thus saves houses and lives
Electrocution: harm caused by an electrical current