This page describes how you can use 120V rated US devices in the UK, where the mains is 240V.
People moving from US or Canada to the UK or Europe sometimes bring portable appliances with them which they would like to use in their new country of residence. Some devices are universal but this is very often not the case and you may need a transformer that could cost more than the device is worth. This page should enable you to determine what you need, if anything.
- Simply plugging a North American device into a European mains socket, perhaps via a simple adapter may well destroy the device and may create a fire hazard.
Mains supply standards
The "electrical pressure" is measured in Volts. In North and Central America the mains supply is between 100 and 127V (120V in the US and Canada) whereas in the UK, Europe and many othe parts of the workd, it's between 220 and 240V (230V in Europe and 240V in the UK).
There are also 2 different standards for mains frequency (50 or 60HZ) but this is practically never of any consequence and so can be ignored. However, a North American clock using the mains fequency for its time standard would loose 10 minutes every hour. Anything containing a fan, the fan will run about 17% slower.
Checking the Ratings
First of all, you need to look at the ratings plate of the device, usually on the back or underneath. There are 2 key ratings to look at:
- The voltage, which we've already discussed, and
- The wattage. This is the amount of power the device takes, and it'll be written as something like 40W, or 750W (or any other number of watts).
Some devices (in particular TVs, audio equipment and mains chargers and adapters) may be universal, having a voltage rating spanning both standards (e.g 100-240V). In order to use such a device, all you need do is to change the plug, or use a simple adapter. For a universal device having a detachable mains lead such as a laptop adapter or computer you can just swap the mains lead for a UK or European one. There are three common types. Search online for "3 pin cloverleaf cable" or "2 pin figure of 8 cable" or "IEC cable" and select one with a UK or your national type of mains plug. It will be obvious which of the three types you need from the pictues on the adverts.
Some other devices such as older HiFis may have a switch near the mains inlet, allowing them to be used on the other mains standard. You will probably need a screwdriver to change it. You will then just need to change the plug, or possibly use an adapter or replace the detachable mains lead, if it has one.
If your device is rated 120V only (or anything from 100 - 127V) you will need a step-down transformer to drop the voltage. This is where the power rating of your device in Watts is important. Note that if you're planning to run more than one device off the same transformer, it needs to be rated for the total wattage of all the devices.
Transformers, particularly the higher-rated ones, are often rated in VA, instead of Watts. For nearly all purposes you can regard them as the same so long as you have a margin of 10 - 20%.
If you search online for "step-down transformer" you should find plenty with various ratings from 45W to 3KW (or 3KVA) and more. At the cheaper end there are some of poor quality, best avoided. These may lack a CE mark, or have universal output sockets where the live contacts would be easy to touch with any metal object. One advertised as an "autotransformer" is suitable, but it won't provide the additional protection of mains isolation that a regular transformer will.
Builders often use 110V power tools with a step-down transformer, particularly when working outdoors. This is for safety: the lower voltage is less dangerous, and the transformer provides isolation from the mains. You could use one of these, but the output is normally via one or more yellow 16A round pin sockets. You would need to make up your own adapter with a 16A plug, a short length of mains cable and a US flying lead socket or multi-way mains block.