Ground Fault Circuit Interrupter (GFCI)

Most people understand that water and electricity are a dangerous combination. Water conducts electricity very well and even a few drops in the wrong place can cause an electrical fire, serious injury or even death. Considering the number of electrical appliances (lights, pumps, filters, heaters, etc.) used in conjunction with saltwater aquariums, installing a Ground Fault Circuit Interrupter is a quick, inexpensive method for protecting yourself, your home and your aquarium equipment.

What is a Ground Fault Circuit Interrupter, and how does it protect you? explains in further detail.