Health and Safety
Executive / Commission
Local authority circulars
To: Health and Safety Enforcing Authorities
For the attention of: Local Authority Health and Safety Enforcement Managers, Health and Safety Regulators and others
1 This circular gives guidance on the use of portable electrical equipment in places where the electric shock risk is increased because the space is restricted and large areas of conductive surface (such as metal) can be touched. Such places are known as restrictive conductive locations and are defined in the current edition of BS 7671 Requirements for Electrical Installations. Section 606 of BS 7671 contains requirements for electrical equipment in restrictive conductive locations.
2 Where a person using portable electrical equipment is in close proximity to, or in continuous contact with, an area of earthed metalwork, the consequences of an electric shock resulting from certain types of failure of the electrical equipment are likely to be serious or fatal. In hot or humid conditions the problem will be made worse by perspiration leaving the skin damp; there may also be a temptation to wear light clothing or to leave parts of the body uncovered. These factors reduce the benefit of any insulation which layers of dry clothing may provide. The use of mains fed electrical equipment in such locations should be actively discouraged and the use of alternatives such as battery powered or pneumatically driven tools preferred.
3 The variability of conditions makes it difficult to give definitive advice but the following points should be borne in mind in relation to work in ducts, shafts, metal cubicles, tanks, etc and in maintenance activities.
4 Wherever possible lighting should be supplied at very low voltages (25V or less). Battery hand lamps may be used or a safety extra-low voltage supply isolated from earth, this is known as a SELV ( separated extra-low voltage) supply. If the supply is derived from a mains-powered transformer, the transformer must be of the double-wound type having an earthed screen between the windings. The transformer should be situated outside the location.
5 Electrically driven hand tools should operate at the lowest practicable voltage. One option is to use battery powered tools; another option is to use tools supplied from a SELV system with a maximum operating voltage of 50V ac however, such tools are not readily available and other options will usually be adopted. A system providing reasonable safety is the 110V centre-tapped to earth system (CTE) which limits shock voltage to earth to 55V.
6 In dry conditions the safety of a CTE system is enhanced by the use of Class II (all insulated or double insulated) hand tools. The double insulation symbol is usually marked on equipment to show that it complies with a standard such as the British Standard for this type of equipment BS EN 60745 (older equipment may be marked to BS EN 50144). The transformer or generator supplying the 110V should be outside the location and arranged so that the centre tap of the 110V winding is connected to earth to give a voltage of 55 between each pole of the supply and earth (63V in the case of 3 phase systems). Transformers should be double-wound isolating transformers to the requirements of BS 3535 (see also BS EN 60742 and BS EN 61558) and generators should have windings which provide electrical isolation equivalent to that of an isolating transformer. It is preferable that each pole of the electrical supply should be fused to give adequate protection against short circuits. No objection should be made to the use of 50V systems centre-tapped to earth with 50V Class 1 (i.e. earthed) tools and 25V hand lamps.
7 All metalwork and cable armouring including the frame of any generator or transformer and that of the work location should be electrically bonded together and to earth to provide an efficient and effective earth path.
8 Certain environmental conditions, e.g. wet or dusty, may impair the degree of protection offered by a Class II portable tool. In such conditions the use of Class I tools may be more suitable, however their performance may also be impaired and protection against electric shock in these circumstances would always depend on the integrity of the earth path (protective conductor) and the suitability of the fault protection. It is preferable for electrical equipment to be constructed so as to exclude water or dust by selecting equipment having an appropriate IP rating (Index of Protection) - see BS EN 60529 'Specification for degrees of protection provided by enclosures (IP code)". When environmental conditions are severe the use of electric tools, other than battery operated, should be questioned.
9 Special attention should be given to the maintenance of electrical equipment which is to be used where there may be adverse environments e.g. wet, hot, oily or corrosive. The equipment must be maintained in good order. Flexible cables are particularly liable to damage and must be suitable to withstand the proposed environment and usage. They should be kept in good condition. In some circumstances it may be appropriate to use cables which are armoured by a flexible metal braid.
10 Additional information on the safe use of electric handlamps can be found in the following Guidance Note: