Safety switches are known by numerous names but all are designed for the same purpose
. In the U. S. They're commonly called a GFI (ground fault interrupter) or GFCI (ground fault circuit interrupter). They're typically found in areas where water is present such as kitchens, bathrooms and outdoor locations like swimming pools and hot tubs. The benefits of electrical safety switches have caused them to be a required installation in many of today's building codes.
Also known as Earth Leakage Circuit Breakers (which is an accurately descriptive name) or Ground Fault Interrupters (GFI's), their job is to prevent you from being electrocuted when you accidentally touch an energized (hot) circuit. They're most prevalently used in areas that contain water, as water can easily cause a person to be 'grounded' and, if shocked, will intensify the effect.
Here's how the system works. A safety switch uses a differential transformer to monitor the 'balance of power' coming in and returning through the protected circuit. The current measurement from the hot and the cold wires should be the same. If not, there's a problem! A properly operating GFI will sense that imbalance and shut off the flow of current.
When a victim is electrocuted it normally sends his heart into ventricular fibrillation (V-Fib). This is a type of heart attack that has killed many but a GFI can prevent this from occurring. It operates in a FRACTION of a heartbeat!
It's important that you test your safety switches regularly. They have a built-in function for this very purpose. All you have to do is press a button and see if it responds correctly. If it's not working it can't help you.
It's difficult to overstate the benefits of electrical safety switches. They're not expensive, they're easy to install and maintain and they, in fact, save lives. What else is there to say?