Single-core polyvinyl chloride-insulated cables in conduit (fixed internal wiring; less common in domestic installations) Flexible cords Supply side wiring 2-, 3-, or 4-core polyvinyl chloride-insulated, steel-wire armoured, polyvinyl chloride-sheathed cables Polyvinyl chloride-insulated, polyvinyl chloride-sheathed (unarmoured cables) 3- and 4-core XLPE-insulated, steel-wire armoured, polyvinyl chloride-sheathed cables Selection of conductors and circuit breakers The selection of conductors must be made taking into consideration both the maximum voltage drop allowed at the load end and also the current carrying capacity of the conductor. Conductor size and voltage drop tables are available to determine the selection, which will be based on the load current supplied. The choice of circuit breaker is also based on the normal rated current of the circuit. Modern circuit breakers have overload and short circuit current protection combined. The overload protection is for protection of the equipment against sustained small-to-medium increase in current above the rated current, while short circuit protection is for the protection of the conductors against high over-currents due to short circuits. For domestic circuits the following choices are typically adopted for selecting conductor and circuit breaker sizes. For distribution boards the incomer circuit breaker rating depends on the current demand at that board. For this the maximum demand and diversity are taken into consideration, based on which the probable current is calculated. Diversity is the condition that all appliances are not likely to be working all at the same time or at their maximum ratings. From this the maximum demand is calculated and the currents are added to determine the load current and hence the rating of the circuit breaker. IEE recommends these current demands and diversity factors for various loads to determine the load current and rating of overcurrent protective device. Special locations Bathrooms The installation of electrical devices in bathrooms and shower rooms is regulated in Section 701 of BS 7671:2018, and Part P of the Building Regulations in England and Wales. For such rooms, four special zones are defined, in which additional protection is required for electrical facilities: Zone 0 is the smallest cuboid volume that contains the bath, shower basin, etc. Zone 1 is the area above zone 0, up to a height of 2.25 m above the floor. Zone 2 is the area above zone 1 up to a height of 3 m, as well as the area that is horizontally within 0.6 m from zone 1. Older regulations defined zone