Safety information
- Nature of hazard
- Effects of electricity on the body
- Overcurrent and short circuit protection
- Earthing
- Earth leakage
- Other protective strategies
- Unenclosed joints in insulated cables
Nature of hazard
Electricity can shock, burn, damage nerves and internal organs or kill people and animals. It can also cause property damage.
Injury or damage can be almost instantaneous and without warning. Recovery can be very difficult with permanent scarring, nerve damage or interference with the functioning of the heart (the heart may not resume normal functioning even after the electricity is disconnected from the body).
The release of energy from major faults can be very large and create an explosion or fire. Even minor faults can be a source of fire that can go on to cause serious property damage and risk to life.
Western Australia has a fatality rate of about 2 people per million population (2001). This compares with Australia at 1.5 people per million [32 deaths] in 2001. This is still too high but much lower than the total of 5.1 people per million [80 deaths] for Australia in 1985. However, it must be accepted that, for the number of the users of electricity and the extreme hazard, 1.5 fatalities per million population is 99.99985% successful use.
Effects of electricity on the body
The effects of electricity on the body depend on the magnitude and duration of the current and the path of the current through the body. The impedance (resistance) of the human body depends on the voltage and duration of contact, any insulation such as gloves, clothing and footwear well as the resistance of the skin.
Depending on current and time, the effects on the human body can range from no effect to ventricular fibrillation, cardiac arrest, breathing arrest and heavy burns.
Ventricular fibrillation is the usual cause of death from contact with 230 volt electricity supply. With high voltage (more than 1,000 volts), the currents that flow can be very large and the burning and damage to internal organs of such large currents is often fatal.
With ventricular fibrillation, the heart loses its capacity to pump blood around the body with the heart muscles contracting in a random disordered way. Normal heart rhythm is not generally re-established when the electricity is removed - the heart may have to be shocked into normal rhythm by a defibrillator.
The effects under normal circumstances are magnified when the resistance of the skin is reduced, such as in swimming pools and in some medical procedures. In swimming pools and special medical procedures, the electrical safety requirements are set higher. Where the heart or its circulation is directly exposed to electricity, shocks can occur at very small currents (100 micro amps). Australian Standard AS 3003 has more information on medical protection.
For a more detailed description of the effects of electricity on the body, refer to AS 3859 - "Effects of current passing through the human body".
Overcurrent and short circuit protection
All electrical wires and appliances have a resistance which generates heat when current flows. An electrical radiator is a simple example. However, the temperature rise in the wires and appliances is designed to stay within limits so that the components and surrounding materials do not degenerate or burn and fires are not caused.
When there is a short circuit, current flows are very large and the temperature rises accordingly. To ensure temperatures are contained to safe limits, over-current and short-circuit protection is provided. The wires and components have to be specified to accommodate expected normal and abnormal conditions.
Referring to the following diagram, there is a wire from the supply (active - A) to the appliance, which may be connected directly or via a plug and socket, and there is a return wire (neutral - N).
Electrical circuit with circuit breaker
Now, if there is a fault in the appliance so that the active wire comes into contact with the metallic case of the appliance, the case will be at 230 volts. If the case is not touching the ground or is insulated from ground or the ground resistance is high (as it usually is), then the current that would flow would not cause the circuit breaker/fuse to operate and disconnect the circuit.
However, should someone touch the appliance, this would cause current to flow, through the person, which could be sufficient to give an electric shock or cause an electrocution.
Earthing
To prevent this danger, a safety system is also installed - an earth wire is connected to the case of the appliance.
Electrical circuit with earth
In this example, if the active wire should become connected to the case of the appliance, a short circuit would occur and a very large current would flow, causing the circuit breaker/fuse to open the circuit. This disconnection should occur in less than 400 milliseconds (0.4 s) which should prevent a fire or other damage. However, this might not prevent an electric shock if the current is high enough.
Earth leakage
In normal circumstances, all the current in the active wire returns via the neutral wire. But, if there is a fault enabling some of the current to go to earth (leakage), the balance is not maintained or there is some residual current. A residual current device (RCD) measures this level of the leakage and if it exceeds a certain level, the RCD opens the circuit. A RCD typically disconnects the supply in 40 milliseconds (0.04 s) for a leakage of 30 milliamps (0.03 A). These levels will usually ensure the possibility of electric shock is very low. For medical installations, 10 milliamp safety switches are used.
It is important to note that a safety switch will not protect all circumstances, such as contact between active and neutral without earth being involved, or between active and active.
Other protective strategies
To complement protection systems, only licensed people should carry out electrical installing work. To 'do it yourself' (DIY) is of great danger to the person carrying out the work and the users of the installation. Also, appliances that are inherently 'risky' have to be approved by the Director of Energy Safety before they can be sold or hired.
Further information on electrical appliances.
Unenclosed joints in insulated cables
During the 1970s and early 80s, joints in electrical cables in ceiling spaces of dwellings and buildings were often only wrapped in insulating tape. The insulating tape dries out over time and may have fallen away, presenting an electric shock risk to persons who enter the ceiling space.
Where a premise is found to contain unenclosed joints, the electrical contractor / electrician is to inform the owner/occupier of the situation and advise that remedial work is to be carried out. At that time, the electrical contractor / electrician will issue an advisory letter (provided by EnergySafety) to the owner/occupier, to apprise the owner/occupier of the situation and associated hazards.
If the occupier is not the owner of the premise, the occupier is expected to hand the leaflet to the owner.
The electrical contractor will notify the network operator of the situation.
The onus is on the owner of the dwelling/building to have the remedial work carried out, using a licensed electrical contractor.
EnergySafety is committed to ensuring the ongoing safety of the public, industry and consumers and appreciates the support of electrical contractors and electricians in supporting this policy.