What happens if you throw a switched-on hair drier into water?

There are a couple things that could happen, worst of all would be harming yourself. If the dryer was plugged into a working GCFI receptacle, then nothing should happen except the little red button on the GFI would trip. They are designed to trip faster than a heart beat. If the dryer is plugged into a regular plug circuit and if the breaker is working, then it will just trip as this will cause a "short" circuit. If the breaker is not working, then most likely there will be lots of sparks because it doesn't trip. Something should trip, even the 100 amp main should go. The only time you would be in trouble is if you are in between the circuit somehow. ie, you are holding onto the tap at the same time and there is copper plumbing, or you are holding the dryer when you put it in. My recommendation, just don't do that.... Andy The above answer is not entirely accurate. If it is a properly functioning GFI circuit then yes the GFI should trip. The key feature of GFIs is that they detect the difference between the current being supplied and the current returning. If you drop a drier in a bathtub then at least some of the current will be grounded through the plumbing (and you along the way). So the GFI should trip and they trip quickly. However if it is a regular circuit breaker then you do *not* have any guarantee that it will protect you. The water *may* short the drier and cause a large enough current flow to trip the breaker. However it may not. It could have enough resistance to limit the current below 15A or whatever the circuit breaker trips at. In which case it won't trip at all. Regular circuit breakers are there to prevent short circuits from overloading the wiring which would burn your house down. They're *not* there to prevent you from being electrocuted. You, and even a bathtub of water, have resistance which depending on various factors may be enough to avoid overloading a regular circuit breaker.