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The subject of electrical supplies to building sites is dealt with in Chapter 1. It has been decided that a gas supply is not required. As a further public relations exercise it might be worthwhile considering the possibility of including public viewing panels in the hoarding on the north and south sides of the site.
Some examples of the standard images that could be used are shown in Fig. Figure 1.
Management of Health and Safety at Work Regulations. The extent to which the above exercise in planning a site layout would be carried out in practice will depend upon various factors, such as the time and money that can reasonably be expended and the benefits that could accrue in terms of maximum efficiency compared with the amount of the capital outlay.
The need for careful site layout and site organisation planning becomes more relevant as the size and complexity of the operation increase.
This is particularly true for contracts where spare site space is very limited. It may also be needed to provide the power to drive small and large items of plant. Two sources of electrical supply to the site are possible: n n portable self-powered generators; metered supply from the local section of the national grid distribution network. As a supply of electricity will be required in the final structure the second source is usually adopted, because it is generally possible to connect a permanent supply cable to the proposed development for construction operations, thus saving the cost of laying a temporary supply cable to the site.
To obtain a metered temporary supply of electricity a contract must be signed between the main contractor and a local area electricity marketing company. They will require the following information: n n n n n n Address of site.
Site location plan. Maximum anticipated load demand in kW for the construction period. Final load demand of the completed building to ensure that the correct rating of cable is laid for the permanent supply.
Date on which temporary supply will be required. Name, address and telephone number of the building owner or their agent, and of the main contractor. Electricity on building sites 23 To ensure that the supply and installation are available when required by the builder it is essential that an application for a temporary supply of electricity is made at the earliest possible date.
On any construction site it is possible that there may be existing electricity cables, which can be advantageous or may constitute a hazard or nuisance. Overhead cables will be visible, whereas the routes and depths of underground cables can be ascertained only from the records and maps kept by local area supply companies. Overhead cable voltages should be checked with the local area suppliers, because these cables are usually uninsulated and are therefore classed as a hazard due mainly to their ability to arc over a distance of several metres.
High-voltage cables of over 11 kV rating will need special care, and any of the following actions could be taken to reduce or eliminate the danger: n n n Apply to the local area supplier to have the cables re-routed at a safe distance or height.
Apply to have the cable taken out of service. Erect warning barriers to keep site operatives and machines at a safe distance. These barriers must be clearly identified as to their intention, and they may be required to indicate the safe distance in both the horizontal and vertical directions. The local area supplier will advise on suitable safe distances according to the type of cable and the load it is transmitting.
The position and depth of underground cables given by electricity suppliers must be treated as being only approximate, because historical records show only the data regarding the condition as laid, and since then changes in site levels may have taken place.
When excavating in the locality of an underground cable extreme caution must be taken, which may even involve careful hand excavation to expose the cable. Exposed cables should be adequately supported, and suitable barriers with warning notices should be erected. Any damage, however minor, must be reported to the electricity supplier for the necessary remedial action.
It is worth noting that if a contractor damages an underground electric cable that was known to be present, and possibly caused a loss of supply to surrounding properties, the contractor can be liable for negligence, trespass to goods and damages.
These impose duties and expectations on employers, employees and the self-employed, for health and safety responsibilities with regard to the use of electricity. Risk assessment and suitable precautions relating to particular hazards, such as overhead lines and underground cables encountered on site, are contained by the Health and Safety at Work etc.
Section details provision for temporary installations and installations on construction sites.
See also, BS 24 Advanced Construction Technology Code of practice for distribution of electricity on construction and building sites. The supply distribution assemblies used in the installation should comply with the recommendations of BS Specification for distribution assemblies for reduced low voltage electricity supplies for construction and building sites.
This covers the equipment suitable for the control and distribution of electricity from a three-phase four-wire a.
BS EN -2 specifies plugs, socket outlets and cable couplers for the varying voltages recommended for use on construction sites.
The appliances and wiring used in temporary installations on construction sites may be subject to extreme abuse and adverse conditions: therefore correct circuit protection, earthing and frequent inspection are most important, and this work, including the initial installation, should be entrusted to a qualified electrician or to a specialist electrical contractor.
Electrical distribution cables contain three line wires and one neutral, which can give either a V three-phase supply or a V single-phase supply.
Records of accidents involving electricity show that the highest risk is encountered when electrical power is used in wet or damp conditions, which are often present on construction sites. It is therefore generally recommended that wherever possible the distribution voltage on building sites should be V. This is a compromise between safety and efficiency, but it cannot be overstressed that a supply of this voltage can still be dangerous and lethal.
The recommended voltages for use on construction sites are given below: Mains voltage V three-phase: n n supply to transformer unit, heavy plant such as cranes and movable plant fed via a trailing cable; hoists and plant powered by electric motors in excess of a 3.
Reduced voltage V three-phase: n n portable and hand-held tools; small mobile plant up to 3. It is worth considering the use of 50 or 25 V battery-supplied hand-lamps if damp situations are present on site. All supply cables must be earthed, and in particular V supplies should be centre-point earthed so that the nominal voltage to earth is not more than 65 V on a three-phase circuit and not more than 55 V on a single-phase circuit.
Protection to a circuit can be given by using bridge fuses, cartridge fuses and circuit breakers. Adequate protection should be given to all main and sub circuits against any short-circuit current, overload current and earth faults.
Protection through earthing may be attained in two distinct ways: n n Provision of a path of low impedence to ensure over-current device will operate in a short space of time. Insertion in the supply of a circuit-breaker with an operating coil that trips the breaker when the current due to earth leakage exceeds a predetermined value.
BS and BS EN recommend that plug and socket outlets are identified by a colour coding as an additional safety precaution to prevent incorrect connections being made.
Main distribution assembly MDA Control and distribution of mains supply for circuits of V three-phase and V single-phase. Socket outlet assembly SOA Connection, protection and distribution of final subcircuits at a voltage lower than the incoming supply.
Extension outlet assembly EOA Similar to outlet assembly except that outlets are not protected. A very-low-voltage current passes along these conductors between the portable plant and the fixed EMU.
Allowance should be made for regional traditions, material resources and local standards.
The original concept of providing supplementary lecture support material for students of construction is maintained. This book should be read in conjunction with experiential learning in the work place or by observation. The material has since been continuously updated through numerous reprints and full second editions in As a former colleague, it has been a privilege to once again work with Roy, on this occasion revising his original work, and compiling the material into two books: Construction Technology and Advanced Construction Technology.
The content forms a thorough study for all students of building, construction management, architecture, surveying and the many other related disciplines within the diverse construction profession. The original presentation of comprehensive text matched by extensive illustration is retained. Changes in legislation, such as the Building and Construction Regulations, have been fully incorporated into the text; however, as much of the original work as possible has been purposely retained as it contains many relevant examples of existing construction.
Additional material discusses the new developments and concepts of contemporary practice. The two new volumes are complementary, as many of the topics introduced here are further developed in Advanced Construction Technology.