Electrical systems

The relatively new home, or the one with an updated electrical system, will allow for safe and reliable use of the latest electric "toys". But, houses built under older codes often suffer from outdated electrical systems not designed for today's uses.
These older systems typically have a fuse box with a 60 or 100 amp capacity, and individual circuit wires insulated with ceramic tubes and spindle-like knobs ("tube and knob wiring". These systems were designed primarily to be used for simple lighting circuits. The assumption was that most rooms would have a single overhead light and possibly one floor lamp. Such a wiring system, if well maintained, will continue to serve for its original purpose--namely lighting. But the designer of this system could not envision the proliferation of electric appliances.
Our microwaves, video recorders and other electronic toys are items that, in combination, can often cause an overload. In addition, the old wiring systems were not designed to accommodate the many portable heaters on the market today.
Fire Hazards and Electrical Systems
Fire departments list electrical problems as one of the major causes of fires in the home.
Typically, such a fire starts with the homeowner replacing the original 15 amp fuses with, for example, a 30 amp fuse, in the mistaken belief that a larger fuse is better because it blows less often. The homeowner now has inadvertently destroyed the very system designed to protect the home.
The danger lies in the overheating of the wire at its weakest link. An example of this can be seen in attaching a new, higher capacity wire to an old tube and knob circuit. If such an installation is overfused and overloaded, it is possible for the old tube and knob wiring inside the wall or crawl space to overheat and possibly start a fire. The fire can start without blowing the oversized fuse or any other sign of a problem in the new segment of wiring. An inspector or qualified electrician may be needed to determine whether a home has an electrical system adequate for today's needs.

Electrical systems differ around the world. Some use 50 hertz; some 60. Some use 110-120 volts; others 220-240. Some are on all the time, barring an ice storm or earthquake; some run a few hours a day. The plugs are also different so travelers with electrical appliances should ensure that they are adequately prepared.
Dealing with electricity differences can be daunting, but it actually isn't too hard. There are only two main type of electric systems used around the world, with varying physical connections:
110-120 volt, at 60 hertz frequency (in general: North and Central Americas, Western Japan)
220-240 volt, at 50 hertz frequency (in general: the rest of the world, with some exceptions).
If the voltage and frequency for your device is the same as where you are travelling, then you need only worry about the physical plug. (The small difference between 110V and 120V, or between 220V and 240V is within the tolerances of most electrical devices.)
If the voltage for your device is not the same, then you will need a transformer to convert the voltage. Transformers are basically chunks of iron specially-wrapped in wires, which means that they are large and heavy. To use one, you must verify that the voltage is being stepped up (low to high voltage) or stepped down (high to low voltage) in the right direction: plugging a 110-to-220V step-up transformer into a 220V socket will get you 440V and a fried device. You must also make sure that the wattage of your device does not exceed the transformer's limit, as doing so may cause the transformer to overheat and even catch fire.
To convert 240V to 120V, lighter weight "switching" converters are available and can handle larger wattage loads up to 1600 watts. Note that they can only step down voltage, not raise it. The electric waveform they produce is not compatible with digital electronics, so it can't be used to power appliances using any such parts. (And always use high quality surge protection with sensitive electronic equipment.)