Dealing With Electricity
Electrical equipment is used on virtually every site. Everyone is familiar with it, but unlike most other hazards, which can be seen, felt or heard, there is no advance warning of danger from electricity, and electricity can kill. Electrical systems and equipment must be properly selected, installed, used and maintained. Hazards arise through faulty installations, lack of maintenance and abuse of equipment. Accidents happen because people are working on or close to equipment which is either: assumed to be dead, but is in fact live; or known to be live, but workers have not received adequate training or adequate precautions have not been taken. It is essential that the electricity power supply requirements are established before any work takes place. Arrangements for the electricity supply should be completed with the local electricity supplier and the supply system installed. Guidance on requirements for low voltage (ie 400 and/or 230 volt ac systems) can be found in BS 7671.
Electrical equipment used on building sites (particularly power tools and other portable equipment and their leads) faces harsh conditions and rough use. It is likely to be damaged and therefore become dangerous. Modern double-insulated tools are well protected, but their leads are still vulnerable to damage and should be regularly checked. Where possible, eliminate risks. Cordless tools or tools which operate from a 110V supply system, which is centre-tapped to earth so that the maximum voltage to earth should not exceed 55V, will effectively eliminate the risk of death and greatly reduce injury in the event of an electrical accident. For other purposes such as lighting, particularly in confined and wet locations, still lower voltages can be used and are even safer. If mains voltage has to be used, the risk of injury is high if equipment, tools, leads etc are damaged, or there is a fault. Residual current devices (RCDs or trip devices as they are sometimes called) with a rated tripping current not greater than 30 mA with no time delay will be needed to ensure that the current is promptly cut off if contact is made with any live part. RCDs must be installed and treated with great care if they are to save life in an accident.
They have to be kept free of moisture and dirt and protected against vibration and mechanical damage. They need to be properly installed and enclosed, including sealing of all cable entries. They should be checked daily by operating the test button. If mains voltage is to be used, make sure that tools can only be connected to sockets protected by RCDs. By installing an RCD at the start of the work, immediate protection can be provided. Even so, RCDs cannot give the assurance of safety that cordless equipment or a reduced low-voltage (such as 110V) system provides.
Mains equipment is more appropriate to dry indoor sites where damage from heavy or sharp materials is unlikely. Where mains leads to sockets may be damaged, they should be: positioned where they are least likely to be damaged, eg run cables at ceiling height; or protected inside impact-resistant conduit. Alternatively, special abrasion-resistant or armoured flexible leads can be used. Electrical systems should be regularly checked and maintained. Everyone using electrical equipment should know what to look out for. A visual inspection can detect about 95% of faults or damage. Before any 230V hand tool, lead or RCD is used, check that: no bare wires are visible; the cable covering is not damaged and is free from cuts and abrasions (apart from light scuffing); the plug is in good condition, eg the casing is not cracked, the pins are not bent and the key way is not blocked with loose material; there are no taped or other non-standard joints in the cable; the outer covering (sheath) of the cable is gripped where it enters the plug or the equipment. The coloured insulation of the internal wires should not be visible; the equipment outer casing is not damaged and all screws are in place; there are no overheating or burn marks on the plug, cable or the equipment; RCDs are working effectively, by pressing the ‘test’ button every day.
Workers should be instructed to report any of these faults immediately and stop using the tool or cable as soon as any damage is seen. Managers should also arrange for a formal visual inspection of 230V portable equipment on a weekly basis. Damaged equipment should be taken out of service as soon as the damage is noticed. Do not carry out makeshift repairs. Some faults, such as the loss of earth continuity due to wires breaking or coming loose within the equipment, the breakdown of insulation and internal contamination (eg dust containing metal particles may cause shorting if it gets inside the tool), will not be spotted by visual inspections. To identify these problems, a programme of testing and inspection is necessary. This testing and inspection should be carried out by someone trained to do this. As well as testing as part of the planned maintenance programme, combined inspection and testing should also be carried out: if there is reason to suspect the equipment may be faulty, damaged or contaminated, but this cannot be confirmed by visual inspection; and after any repair, modification or similar work to the equipment, which could have affected its electrical safety.
With lighting systems, provide protection for cabling in the same way as for tools. Protect bulbs against breakage. If breakage does occur, the exposed filaments may present a hazard. Make sure there is a system for checking bulbs to maintain electrical safety and also to keep the site well lit. Tools and equipment should be suitable for site conditions. DIY tools and domestic plugs and cables are not designed to stand up to everyday construction work. Also observe other restrictions on use imposed by manufacturers. If work is to be done in areas where there is a risk of flammable vapours (such as in a petrochemical works), it will be necessary to select specially designed electrical equipment to prevent it acting as a source of ignition due to sparks and overheating. Precautions should be covered in the project health and safety plan and the operator of the premises should be able to provide advice. Specialist advice may also be needed.