A circuit breaker that trips when there is a difference between the amount of current in the hot side and the neutral side. Also called a "ground fault circuit interrupter" (GFCI) and an "appliance leakage current interrupter" (ALCI), the current imbalance implies a leakage to ground or another circuit. Residual current devices (RCDs) are typically built into a wall outlet and are required for wet areas, such as bathrooms and kitchens, where electrical appliances can come in contact with water.