422-41. Cord- and Plug-Connected Appliances Subject to Immersion
Cord- and plug-connected portable freestanding hydromassage units and hand-held hair dryers shall be constructed to provide protection for personnel against electrocution when immersed while in the “on” or “off” position.
Although receptacles in bathrooms of dwelling units have been required to be protected by ground-fault circuit interrupters since the 1975 edition of the Code, many receptacles in existing bathrooms are not so protected. Cord- and plug-connected appliances such as hand-held hair dryers, curling irons, and so on, which can and have accidentally fallen into bathtubs, causing fatalities, are required to be provided with some form of protective device that is part of the appliance. Three types of protectors comply with this requirement: ALCIs, IDCIs, and GFCIs.
Appliance-leakage circuit interrupters (ALCIs) are intended to de-energize the supply to the appliance when leakage current exceeds a predetermined value. Immersion-detector circuit interrupters (IDCIs) de-energize the supply when a liquid causes a conductive path between a live part and a sensor. Ground-fault circuit interrupters (GFCIs) de-energize the supply when the current to ground exceeds a predetermined value.
Joe Tedesco, NEC Consultant