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The clear hazards presented by an electrical installation are those associated with the electricity that it distributes within the premises. The level of risk is high simply because of the large number of installations and the close proximity between the installation and people going about their everyday lives. People come in contact with an electrical installation without understanding the associated risk. It is for these reasons that the standard of electrical installations must be maintained at a high level.
The risks are to persons or property or both. Personal risks would primarily be from electric shock or fire, including burns and the effects of smoke inhalation. The risk to property includes a whole range of thermal damage resulting from melting, pyrolysis (chemical decomposition brought about by heat) and fire.
It is useful to define a number of categories of electrical installation when analysing the risks and incidents that have been uncovered in practice:
1. High Voltage Installations
High voltage installations rely on devices to cut the power in the event of a fault. These devices, in turn, rely on a low voltage power supply in order to operate. An example was uncovered of an electrical installation where the power to the protective devices had been disconnected. This resulted in a highly dangerous situation given the destructive power of a high voltage system. The potential for fire related damage was significant.
It is essential to maintain safe clearances from any overhead powerline. A number of metal lighting columns were being erected on a public road reserve using a crane with a significant horizontal reach. While supported by a sling from the crane, one lighting column came within arcing distance of a 66 kV powerline. The subsequent flashover caused the death of one person and burns to another.
Lighting pole held up by sling Evidence of high voltage arc fault
2. Hazardous Areas
There have been a number of examples of unsafe electrical installations installed within a hazardous area. Whilst there have been no recent examples where an explosion has occurred as a result of a faulty electrical installation, there have been several examples where there was the potential for this to occur. Non-compliant installations within a hazardous area present a real possibility of explosion, fire and injury or death. A very common example of this style of installation is the electrical equipment associated with the pump at a petrol station.
Industrial Fire
Industrial fire brought about by electrostatic discharge possibly due to design deficiencies
Electrical Fire in Hazardous Areas
Before and after a fire caused as a result of an inappropriate light fitting installed in a hazardous area
3. Low Voltage - High Energy Fault Currents
A number of people were extensively burnt when an arcing fault was induced between different phases of a main switchboard. The heat generated set fire to the victims - clothing.
In another incident the arcing fault caused an assistant electrician to receive fatal burns. The ends of a pair of pliers were melted during the incident.
Most of the incidents in this category have been due to incorrect procedures for the work undertaken or test equipment that was not correctly used or not suitable for the purpose. There has been evidence of a lack of understanding associated with the destructive power available from a low voltage high current distribution network connection.
Figure: Industrial Switchboard
An example of an installation where a high fault current would be available.
Many of the burn victims have been working on switchboards like this one.
4. Low Voltage - Low Energy Fault Currents
Electrical workers have received fatal electric shocks when working on parts of an installation while it was alive. The test methods to verify the circuit is dead were inadequate or the worker was using inappropriate work methods or not wearing appropriate personal protective clothing and equipment.
Members of the public have received fatal electric shocks performing electrical work without the competencies necessary for performing that work; using extension cords and portable equipment without the protection of a residual current device (safety switch); or using steel ladders with sharp edges which have cut through the insulation of flexible cords.
People have suffered injury and received non-fatal electric shocks from light fittings where the exposed metal has been connected to the active conductor. The light fittings were installed and incorrectly connected by unqualified persons.
Sub-standard Electrical Installation
Example of very poor workmanship, leaving the installation with exposed live parts
5. Extra Low Voltage
The heat generated by extra low voltage down lights has ignited combustible material and caused major damage to premises.
6. Connections to the Network
The connection between the distribution network and the consumer's installation can give rise to significant safety risks. Correct connections and polarity not being verified at the time of connection to the network has caused earthing systems and the exposed metal of appliances and light fittings to become live causing people to receive electric shock and injury and property damage. In many installations the plumbing within the house will be bonded to the electrical earthing system. Reversing the polarity could result in all the plumbing and fixtures (tap ware) being able to cause electric shock.
Control of the Risks Associated with an Electrical Installation
The results of an electrical installation failure are easily seen. However, because of the complex nature of electrical systems, it is difficult for the general public to reliably assess the associated risks. Accordingly the Government has legislated to assist the community to control these risks.
Electricity