RCDs are often used in wet locations, like kitchens and bathrooms, where there is a risk of electrical shock. They are also used outdoors where there might be water, like swimming pools, spas, and hot tubs. Any time you have an electrical outlet near water, you should use a GFCI to protect yourself and your family from accidental electrocution. Modern electrical standards require new installations to have electrocution protection on almost every circuit and outlet in the house.
An RCD monitors the amount of current flowing in a circuit. It does this by measuring the difference between the currents going to and from an outlet. If there is any discrepancy between the two currents—even a tiny one—the RCD will trip and shut off power to the outlet within milliseconds. This happens so quickly that most people don't even realise that there was ever any danger.
RCDs coming in many shapes, types and sizes; although the one thing that all RCD's have in common is a test button. A test button simulates a fault and is used for verifying the function of the RCD to ensure it is still in working order. You can do an RCD test yourself, just press the test button and reset. If it trips and resets without anything untoward, then you know its still good.
Accidental electrocutions are more common than you might think—especially when water is involved. People drown yearly in swimming pools or spas with faulty electrical equipment. And many more are injured or killed in other accidents involving electrical outlets near water.
An RCD is designed to prevent these accidents by shutting off power as soon as they detect a current leak. This makes them essential safety equipment for any home with a pool or spa. The electrical codes now require that RCDs protect all outdoor outlets near water.
If you have lost power and it appears to be due to an RCD tripping, first complete a visual check of the switchboard and any equipment that has lost power. If you notice any electrical damage or burnt smell, do not turn the RCD back on; contact an electrician and explain the situation. Sometimes the RCD trip is due to something minor and temporary, so if there are no visible faults, attempt to reset the RCD.
If the RCD continues to drop immediately, unplug any appliances without power, this will hopefully remove the faulty appliance from the circuit and allow you to reset the RCD. If the RCD does reset after unplugging the appliances, plug the appliances back in one by one until you locate the item causing the trip.
If you have unplugged all appliances and the RCD is still tripping immediately, contact an electrician; there is likely something you cannot disconnect yourself causing the issue, or it is a lighting or cable infrastructure issue.