earth conductor. If large enough, this current will trip an over-current device (fuse or circuit breaker [CB]) and disconnect the supply. The disconnection time has to be fast enough not to allow fibrillation to start if a person is in contact with the casing at the time. This time and the current rating in turn sets a maximum earth resistance permissible. To provide supplementary protection against high-impedance faults it is common to recommend a residual-current device (RCD) also known as a residual current circuit breaker (RCCB), ground fault circuit interrupter (GFCI), or residual current operated circuit-breaker with integral over-current protection (RCBO), which will cut off the supply of electricity to the appliance if the currents in the two poles of the supply are not equal and opposite. Class 0I Electrical installations where the chassis is connected to earth with a separate terminal, instead of via the mains cable. In effect this provides the same automatic disconnection as Class I, for equipment that otherwise would be Class 0 Class II A Class II or double insulated electrical appliance uses reinforced protective insulation in addition to basic insulation. Hence, it has been designed in such a way that it does not require a safety connection to electrical earth (ground). The basic requirement is that no single failure can result in dangerous voltage becoming exposed so that it might cause an electric shock and that this is achieved without relying on an earthed metal casing. This is usually achieved at least in part by having at least two layers of insulating material between live parts and the user, or by using reinforced insulation. In Europe, a double insulated appliance must be labelled Class II or double insulated or bear the double insulation symbol: ⧈ (a square inside another square). As such, the appliance should not be connected to an earth conductor because the high-impedance casing will cause only low-fault currents that are unable to trigger the fusible cut-out. Insulated AC/DC power supplies (such as cell-phone chargers) are typically designated as Class II, meaning that the DC output wires are isolated from the AC input. The designation "Class II" should not be confused with the designation "Class 2", as the latter is unrelated to insulation (it originates from standard UL 1310, setting limits on maximum output voltage/current/power). Class IIFE These devices have a Functional Earth "FE". This differs from a protective earth ground in