[...]... magnitude or type of risk, and an additional classification is usual Table 1.2 is based on BS 4683: Part 1/BS Design of electrical services for buildings 24 EN 50021 Electrical apparatus for potentially explosive atmospheres Types of protection ‘n’, show the classes which are used to designate the maximum permitted surface temperature It is possible for equipment having any type of protection to have... bench trunking For higher current applications, a transformer from the mains, which can either provide a fixed secondary voltage or be of the tap-changing type to give a choice of voltages, or even a variable voltage transformer, may provide the supply A Accessories 19 Figure 1.18 Pattress Figure 1.19 Pattress Design of electrical services for buildings 20 Figure 1.20 Bench trunking (courtesy of M.K Electric... selecting a switch for, Design of electrical services for buildings 4 say, fluorescent lighting It was for this reason that some of the older switches had to be de-rated when they were used for discharge lights, but switches in current production are suitable for inductive loads up to their nominal rating A 5A rating is not as large as one might think at first sight If ten tungsten lamps of 100W 230V each... ingress of large solid foreign bodies 2 Protection against contact with live or moving parts inside the enclosure by fingers Protection against ingress of medium-size solid foreign bodies Design of electrical services for buildings 3 26 Protection against contact with live or moving parts inside the enclosure by tools, cables or such objects of thickness greater than 2.5mm Protection against ingress of. .. the appliance on and off, such as for an electric hand dryer in a public toilet If this is a problem, then unswitched fuse spur units are available They are used to connect mains-supplied equipment in bathrooms, such as Design of electrical services for buildings 8 Figure 1.5 Socket outlets (Courtesy of M.K Electric Ltd) electrically heated towel rails, in zones where connection of such equipment is... surface conduit The inclusion of the box makes it possible for the cables to enter the socket outlet from the back, whereas without it, there would be an untidy junction of the conduit with the bottom of the socket outlet It is now fairly standard practice in commercial situations to install trunking which incorporates the socket outlets Design of electrical services for buildings 18 Figure 1.17 Mounting... Switches (Courtesy of M.K Electric Ltd) Figure 1.4 Double pole switch (Courtesy of M.K Electric Ltd) In order that power equipment can be fully isolated it is often desirable to use a double pole switch This expression means a switch which opens both the phase and neutral circuits The mechanism is similar to that of an ordinary or single pole switch, but there Design of electrical services for buildings 6... likelihood of such a concentration: 1 Zone 0 (ATEX category 1G {Gas}) A place in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is present continuously or for long periods or frequently 2 Zone 1 (ATEX category 2G {Gas}) A place in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of a... consisting of a mixture with air of flammable substances in the form of a gas, vapour or mist is not likely to occur in normal operation but, if it does occur, will persist for a short period only For dusty atmospheres the following definitions apply: 1 Zone 20 (ATEX category 1D {Dust}) A place in which an explosive atmosphere in the form of a cloud of combustible dust is present continuously or for long... safe equipment is designed for operation on extra low voltages It is permissible to limit the current by means of a barrier diode This type of protection is designated type i; it may be designated type ia or type ib according to the number of faults it can sustain during testing Table 1.1 is based on BS EN 60079–14:1997: Part 1, Electrical apparatus for explosive gas atmospheres Electrical installations . x0 y0 w0 h0" alt="" Design of Electrical Services for Buildings, 4th Edition Design of Electrical Services for Buildings, 4th Edition Barrie Rigby. provide a basic grounding in the design of electrical services for buildings. It is intended for students of building services engineering in universities