on a horizontal centre line, 60.3 mm apart. Double face plates for BS 4662 boxes measure 147 mm × 86 mm and have the two screws 120.6 mm apart. Accessories in the BS 4662 format are only available in a comparatively limited range of designs and lack the product diversity and design sophistication found in other European markets. The UK installation-accessory industry is therefore occasionally criticised for being overly conservative. As many modern types of electrical accessories (e.g., home automation control elements from non-UK manufacturers) are not available in BS 4662 format, other standard mounting boxes are increasingly used as well, such as those defined in DIN 49073-1 (60 mm diameter, 45 mm deep, fixing screws 60 mm apart) or, less commonly in the UK, ANSI/NEMA OS-1. The commonly used domestic wall-mount socket used in the UK for currents up to 13 A is defined in BS 1363-2 and normally includes a switch. For higher currents or three-phase supplies, IEC 60309 sockets are to be used instead. Many high load non-UK-sourced appliances need IEC 60309 connectors (or wiring via a British Standard "20 A connection unit") in the UK because of the lower plug rating. Plug and accessory fuses (or, cartridge fuse) Flexible appliance cords require protection at a lower current than that provided by the ring circuit overcurrent protection device. The protection device may be contained within the appliance plug or connection unit, and is normally a ceramic cartridge fuse to BS 1362:1973, commonly rated at 3 A (red), 5 A (black), or 13 A (brown), but some accessories and adaptors use a ceramic cartridge fuse to BS 646:1958. In the case of permanently connected equipment, a fused connection unit (FCU) to BS 1363-4 is used, this may include an isolator switch and a neon bulb to indicate if the equipment is powered. In the case of non-permanently connected domestic equipment, a BS 1363-2 socket rated at 13 A is attached to the ring circuit, into which a fused plug may be inserted. (Note, it is not intended that the fuse should protect the appliance itself, for which it is still necessary for the appliance designer to take the necessary precautions.) Multiple socket accessories may be protected with a fuse within the socket assembly. Residential wiring Cable types In domestic wiring, the following cable types are typically used: Internal wiring Twin and earth polyvinyl chloride-insulated and -sheathed cables, or