use outdoors or in other wet locations (but not bathrooms) special sockets are made. These can be divided into three main groups: industrial sockets, which are totally different from the standard sockets; sockets with the same pinout as normal sockets but that will only seal properly when the correct plug and socket are used together (e.g., the 5 A, 13 A, and 15 A variants of Lewden sockets); and sockets that completely enclose a normal plug with a seal around the flex (e.g., MK Masterseal). Sockets that are outside or can "feasibly supply equipment outside the equipotential zone" (a wording that is fairly ambiguous and the exact interpretation of which is subject to some controversy) should be protected by a 30 mA, or lower, RCD to provide additional safety. Since 2008, all sockets for general use should be RCD protected, removing the questions that used to arise, such as if a socket by the door might power a lawnmower does it need an RCD? Construction sites The risk of electrical shock on construction sites can be reduced by several measures, including reduction of the normal 230-volt distribution voltage to 110 volts for electrical lighting and power tools. By using a centre-tapped transformer, each conductor of the circuit is only at 55 volts with respect to earth. This reduces the chance of dangerous electrical shock when using power tools in wet locations. Where 230 volts must be used, a residual current device (RCD) can be used to detect small leakage currents and automatically isolate faulty equipment. In sites where hazardous flammable gases or liquids are present, special wiring rules are applied to reduce the probability of a spark igniting a fire or explosion. Legal and regulatory Legal basis In England and Wales, the Building Regulations (Approved Document: Part P) require domestic electrical installations to be designed and installed safely according to the "fundamental principles" given in British Standard BS 7671 Chapter 13, most recently updated in July 2018. These are very similar to the fundamental principles defined in international standard IEC 60364-1 and equivalent national standards in other countries. Accepted ways for fulfilling this legal requirement include: the rules of the IEE (IET) wiring regulations (BS 7671), colloquially referred to as "the regs". The current version of this standard is the 18th edition, formally known as BS 7671:2018 Requirements for Electrical Installations. IET Wiring Regulations; the rules of an equivalent standard