WARNING! - Please read the following carefully

The information described in these pages details utilizing POTENTIALLY FATAL HIGH VOLTAGES. If you are unfamiliar with high voltage applications or are uncomfortable working around high voltages, PLEASE DO NOT RISK YOUR LIFE. Seek help from a competent and accredited electrician.

The following information is provided with no guarantee of any kind! USE AT YOUR OWN RISK.

USA->Australia Electrical Appliance Considerations

I compiled the following information regarding electrical appliance power considerations between the USA and Australia when I moved back to Australia in 2001. Hopefully this information will help others decide if they should ship their electrical appliances to Australia, or dispose of them in the USA and replace them on arrival in Australia.

  • Normal USA household mains power is delivered as 115V 60Hz AC.

  • Normal Australian household mains power is delivered as 240V 50Hz AC.

  • Electrical appliances, electronic equipment and other electrical devices purchased in the USA contain an information plate explaining the valid AC voltages and frequencies or DC voltages that can be used to power the given device.

    • These information plates also outline the expected power consumption of the device. Power consumption is measured in watts, e.g. 1000W.

    • If power consumption is not indicated then the operating current of the device will be listed. Electrical current is measured with amperes, e.g. 10A.

    • Ampere measurements are associated with a particular operating voltage. For example, 115V, 10A. To convert this information to power consumption, multiply the operating voltage by current. E.g. 115 * 10 = 1150W.

  • If an appliance information plate does not indicate that the appliance can be powered at 240V, but only 115V, then powering that appliance in Australia at 240V will normally result in non-operation of the appliance.

    • A typical outcome for powering a 115V rated appliance at 240V is the destruction of the power system in the appliance, sparks, flame, heat, smoke and the creation of an electrocution hazard.

    • Being careless with 115V electrical appliances in Australia can result in injury or death.

    • This applies to both active devices, e.g. a fax machine, and passive devices, e.g. many 115V power boards with "surge protection".

  • Most non-computer electrical appliances sold in the USA are not rated for 240V and therefore cannot be powered directly from a household mains socket in Australia. However, for many 115V appliances, a transformer can be used to step down 240V to 115V and provide a safe power supply.

    The following issues arise when using a transformer to step down 240V to 115V:

    • Transformers only modify voltage, they do not modify the frequency of AC electricity. The power information plate on the appliance should indicate that the appliance can be operated at 50Hz (the AC frequency in Australia). On many USA purchased appliances this is often denoted as 115V 50Hz-60Hz or 50/60Hz. If the appliance does not specifically indicate that it can be operated at 50Hz then operation at that frequency may lead to the non-function of the appliance, power supply failure or other hazards. If an appliance does not identify itself as being able to operate at 50Hz then some further steps can be attempted.

    • Transformers must be rated to handle the peak power requirements for all concurrently running connected 115V appliances. If an attempt is made to draw more load through the transformer than its rating then possible outcomes are overheating or failure of the transformer or failure of the connected appliance power supplies. In turn this could cause smoke, sparks, flame and may create an electrocution hazard.

    • Two general types of transformers are available to step down 240V to 115V, isolation transformers and autotransformers.

    • A grounded isolation transformer physically isolates the 115V appliance from the 240V mains supply. The 115V active output wire is physically separated from the 240V active input wire. This type of transformer is sometimes referred to as "double wound".

    • A grounded autotransformer provides 115V on output via a center tap on a single winding of which each end is connected to the active and neutral 240V wires respectively. This means that the output 115V active power wire is connected directly to the input 240V active power wire, i.e. for DC electricity there is 0 Ohms resistance between the input 240V wire and the output 115V wire! Because of this design feature autotransformers are usually considered less safe than isolation transformers.

    • Only grounded isolation transformers or grounded autotransformers should be used for high power appliances. This means that the ground pins, if any, on the 115V appliances have a direct path back to the ground wire in the house. Modern Australian houses utilize a residual current device to detect any small amount of current between the active (or hot) wire and earth. If a small amount of current, e.g. 30mA, is seen on this circuit then the residual current device trips and disconnects the active and neutral household supply wires from the street supply.

      Do not subvert the residual current device safety feature by connecting the ground wire in an autotransformer or isolation transformer to the neutral wire of the house supply. Such an action could result in injury or death in the case of an electrical fault in the 115V appliance.

    • All transformers exhibit some amount of inrush current when the active input is applied. The amount of inrush current is a function of the power capacity of the transformer as well as the design of the transformer. It is not unusual for inrush current to result in very brief current requirements of well over 10 times the rated output current of the transformer. See this page for information about dealing with large transformer inrush current problems with circuit breakers.

    • Consider installing a fuse or breaker on the output side of a large current transformer. A transformer that is rated to deliver power to 2000W appliances is also capable of delivering a lethal dose of electricity to a person.

  • Some further information:
    • Ameritron ICP-240 240V Inrush Current Protector. Read this first.
    • Western Australia state government information on residual current devices.
    • A good primer on electricity basics.
    • Hammond Manufacturing make 2000W 230V->115V 50/60Hz step down autotransformers. In the USA these can be purchased from Mouser.
      Notes about the Hammond 170JE:
      • It emits a loud 50Hz audio hum making it unsuitable to operate while it is physically located inside a house. Update: I've received a note from Hammond that they've done some work to reduce the hum in their more recent version of this transformer.
      • The 170JE is large and very heavy.
      • Even unloaded it gets very hot.
      • It has an enormous inrush current that will almost always trip a typical modern Australian circuit breaker. See this page for more information.
      • It is relatively inexpensive.
      • Prior to shipping Mouser will ask you to sign a paper giving up your ability to return the transformer for refund.
      • Hammond appears to make these autotransformers "on demand". The specification plate on the autotransformer will likely contain a manufacturing date that is some time after you placed the order. This implies a lead time of several weeks. Update: Hammond now inventories this transformer so the lead time is reduced.
      • The base mounting plates will likely arrive bent, probably due to the box being dropped during shipping. Update: Hammond has reworked their packaging so this problem should now no longer occur.
      • The 170JE works very well.
    • In Australia Soanar are a reasonable and reliable source for 230V->115V isolation transformers and autotransformers. "Steed" Chinese made autotransformers are available up to 1000W and isolation transformers up to 500W. The Steed 500W isolation transformer does not have a 50Hz audio hum and does not get too hot during continuous moderate use, so is an ideal candidate for medium power inside-the-house (i.e. non-toolshed) applications.
    • Hammond "big iron" autotransformers can be ordered through their office in Australia:
      Hammond Electronics Pty Ltd
      ABN 13 099 121 981
      GPO Box 812
      SA 5001
      Tel: +61-8-8235-0744
      Fax: +61-8-8356-3652
      Email: ccookson@hammfg.com
    • Australian retail outlets for Dick Smith and Radio Shack also stock suitable transformers, but check the price.