Using electricity
Although most people still use the term '240 volt power' to refer to mains power, the official standard is now a nominal 230 volts. The voltage is 'nominal', because it's actually allowed to vary between 216 and 254 volts at any given time, so that the distribution system can cope with different usage and supply levels in the power grid.
Mains power in Australia is supplied as 230 volt single-phase alternating current (AC) electricity. Standard power points are designed to take two-pin or three-pin plugs. One pin connects to the active or live wire. The opposing pin connects to the neutral wire, which completes the circuit. And the bottom pin has no role in delivering electricity, but connects the tool to the earth wire as a safety mechanism, in case there is a malfunction or 'short circuit'.
Note that large static machines do not generally run on mains power, but are connected instead to 415 volt three-phase power. This is used with machines that are built to operate continuously for long periods, or need extra power to carry out industrial processes.
Fuses and circuit breakers
Power circuits are always protected either by a fuse or circuit breaker. If the system is overloaded or a fault develops, the fuse is designed to blow, or the circuit breaker to trip, which cuts off the power supply.
Fuses must only ever be replaced by fuse wire of the same amperage as the original, because if you used heavier fuse wire than the original, you wouldn't have the same level of protection, and if you used lighter fuse wire it would blow too easily. Note that when a fuse or circuit breaker blows repeatedly it is an indication that there's a problem which needs to be fixed. So if it happens when you plug a particular tool in, you should tag the tool as 'faulty' and put it in for repairs.
Insulation
There are three systems of insulation used in power tools:
Single insulated tools use an earth wire which is connected to the metal casing of the tool at one end and the earth pin of the plug at the other end. In the event of a fault that causes a short circuit, the current is able to flow straight to earth without giving the operator an electric shock.
Double insulated tools use two layers of insulation between the internal parts that carry a current and the outer metal parts of the body. For this reason, they are not connected to an earth wire.
All-insulated tools are fully encased in plastic or other insulating material, with no exposed metal parts. Again, they are never earthed, even if they are supplied with a three-pin plug.
Safety considerations
Mains power is used everywhere, but that doesn't mean you should take its safety for granted. Every year people are hospitalised as a result of electric shock, and occasionally the shocks prove fatal. Electrical faults are also responsible for many fires, because the sparks from short circuits or heat from over overloaded wires can ignite flammable substances or materials.
However, there are some simple procedures you can follow to minimise the chance of suffering a shock or starting a fire. Select the links below for more information.
Testing and tagging of power tools
Learning Activity
View from the back of a three-pin plug.
You can use print this diagram to use for your exercise, or copy it for your own drawing of the power plug.
Note that the socket on the other end of an extension lead will have the active and neutral terminals reversed when viewed from the back, so that they match the pins on the plug.
The colour codes for mains power wiring in Australia has conformed to the International Standard for some years. However, you may still find old extension leads and power tools using the colour codes that applied before the new standard was adopted.
Go out into your workplace and look for some see-through three-pin plugs or sockets. You will be able to see the colours used on the wires, and which pins they are connected to.
Draw the back of a power plug on a piece of paper.
Mark the Active terminal with an 'A'
Mark Neutral with an 'N'
Mark Earth with an 'E'.
The diagram below shows the old and new standards that apply.
Wire | New colour code | Old colour code |
Active (A) | Brown | Red |
Neutral (N) | Blue | Black |
Earth (E) | Green/Yellow | Green |