Electrical current used in most homes is what is called alternating current. Invented by Nicoli Tesla, it is the most practical method of transmitting power because it travels in "waves". The electrons, which are the subatomic particles that move in electricity, only move a short distance back and forth instead of traveling all the way from the power plant to your home and back. The resistance to the flow of electricity in the wires has much less effect making alternating current cheaper to transmit. It also allows the use of transformers to change voltage up or down. Electricity consists of voltage which is the "pressure" or amount of push behind the electrons and current (or width of the pipe) measured in amperes. The total amount of power used is measured in WATTS which are voltage times amperage. Since the electricity flows in waves, the voltage changes constantly. The two measurements used are peak voltage which is the highest voltage and RMS (root-mean-square) which is the approximate voltage it would be if it did not alternate (direct current). To find the RMS voltage, divide the peak by .707 (square root of 2 divided by 2). When you buy an appliance its power requirements are specified using the RMS voltage (assumed to be 120 volts in the US). Transformers are rated in PEAK volts times current called volt-amperes, but usually mistakenly called watts. So when you buy a transformer you need to calculate it can safely handle by multiplying the rated watts by .7 to calculate the "real" watts. There are 3 types of voltage adaptors sold. The first is a true transformer. They are the most expensive type. The true transformer has two separate coils wound around an iron core. Their advantages are that the output voltage is closer to the same at all loads and there is no direct connection to the power line. The disadvantage is they are less efficient. In transformers all wasted electricity becomes heat. The second type is an "autotransformer". This is one coil wound around an iron core. The iron core and windings are smaller and cheaper than a true transformer. Their disadvantage is that you are directly connected to the power line and the voltage output varies depending on the load. The third type are resistors which limit the flow of electricity. They waste lots of power and put out an equal amount of heat to the load. These are the 1500 watt converters for hair dryers etc, and are IMHO dangerous and worthless. For most uses an autotransformer is the best to get. We use an autotransformer for GE refrigerator.(see note below). When you by an autotransformer make sure you get one designed for CONTINUOUS DUTY (on all the time) and rated for the correct load. I usually buy them rated for twice what I intend them for. For example, I use 200 watt autotransformers available here for 45 NIS for loads of 100 watts or less. I prefer to use one for each device instead of one big one for many devices, but I share one for all the 120 volt devices on my computer. The second thing to consider is frequency. The number of waves per second is called the frequency and is measured in Hertz (Hz). The household current in the US is 60 Hz, the current in Israel is 50 Hz. Clocks use the power line frequency to keep time as do many VCRs. (multi-voltage VCRs do not). Therefore US clocks on a transformer will run 20% slower. The note below: Since the wave is 20% wider, the amount of POWER in a 50 Hz wave is 20% higher than a 60 Hz wave of the same PEAK voltage. Vernon Whetstone (of Sherri's Appliance Service) recommends that you use a special transformer (rated at 100 volts out) for appliances, especially refrigerators. IMHO, if you bring a 120 volt major appliance you should get Vernon to install it. I don't get a commission, so it's okay for me to say this. :-) Another thing to watch is grounding. Most American appliances have a ground connector on the plug. This is because in the American electrical system the ground is part of the circuit and will cause an overload (and hopefully shut off the electricity) if there is an acccidental connection to the ground. In European 220 volt systems this is not true and a ground connection is of less use. Israel uses a hot-neutral-ground system similar to the U.S. Grounding and polarity are important, they should not be ignored or circumvented. The U.K. uses a similar system to Israel, so U.K. made applicances (with grounds) are prefered over European non grounded ones. Most of the 220 to 120 volt autotransformers sold here have a socket to accommodate grounded plugs, but do not carry the ground connection through. If you have a device that needs grounding (has a 3 prong plug), you must ground it, get the correct autotransformer. What should you do and how do you protect yourself? 1. Buy appliances made for Israel, as opposed to 220 volt european appliances. Applinaces made for sale in the U.K. also have the proper ground. 2. If you buy European 220 volt appliances, make sure they are "double insulated". For example, this would be blender or drill with an all plastic case and handle. If you do buy a "double insulated" appliance discard it if the case breaks or cracks. 3. Replace the main circuit breaker in your home with a Ground Fault Interupter*. Israel Electric has a free pamphlet in Hebrew describing this. 4. Make sure that any transformers you buy have grounded plugs and sockets on them. Also make sure the ground is connected from both sides. 5. When you want electrical work done, consult a competent elecrician.