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ELECTRICITY AT WORK ACT 1989

Means for cutting off the supply and for Isolation Regulation 12(1) (a) 182 The objective of thispart of the regulation is to ensure that, where necessary to prevent danger, suitable means are available by whichthe electricity supply to any piece of equipment can be switched off. Switching can be, for example, by directmanual operation or by indirect operation via ‘STOP’ buttons in the control of contactors or circuit breakers.There may be a need to switch off electrical equipment for reasons other than preventing electrical danger butthese considerations are outside the scope of the regulations. Regulation 12 (1) (b) 183 Whereas regulation12(1)(a) requires means to be provided whereby the supply of electrical energy can be switched off 12(1)(b)requires that there will be available suitable means of ensuring that the supply will remain switched off andinadvertent reconnection prevented. This is isolation. This provision, in conjunction with safe working practices,will enable work to be carried out on electrical equipment without risk of it becoming live during the course ofthat work, for example if the work is to be done under the terms of regulation 13. 184 In some cases theequipment used to perform the requirement under regulation 12(1) (a) may also serve to perform the requirementunder 12(1) (b). It must be understood that the two functions of switching off and isolation are not the same, eventhough in some circumstances they are performed by the same action or by the same equipment. Regulation12(3) 185 Regulation 12(3) recognises the impracticability in some cases of switching off or of isolating thatequipment which is itself an integral part of a source of electrical energy, for example the terminals ofaccumulators, large capacitors and the windings of generators. The regulation requires precautions to be taken inthese circumstances so that danger is prevented so far as is reasonably practicable. “Where necessary toprevent danger” 186 The need for means to cut off the supply and effect isolation depends on factors suchas likely danger in normal and abnormal conditions. This assessment may be influenced by environmental conditionsand provisions to be made in case of emergencies, such as a fire in a premises. It includes consideration of whichelectrical equipment could be a source of danger if such means were not provided and of the installation,commissioning, operational and maintenance requirements over the life of the equipment. Suitable means forcutting off the supply 187 The suitable means for cutting off the supply (regulation 12(1)(a))should: (a) be capable of cutting off the supply under all likely conditions having regard to the equipment, itsnormal operations conditions, any abnormal operating or fault conditions, and the characteristics of the source(s)of electrical energy; (b) be in a suitable location having regards to the nature of the risks, the availability ofpeople to operate the means and the speed at which operation may be necessary. Access to switches etc. should bekept clear and unobstructed, free of tripping and slipping hazards etc; (c) be clearly marked so as to show itsrelationship to the equipment which it controls, unless there could be no doubt that this would be obvious to anyperson who may need to operate it; and (d) only be common to several items of electric equipment where it isappropriate for these to be energised and de-energised as a group. Suitable means ofisolation 188 The suitable means of isolation of equipment (regulation 12(1)(b)) should: (a) have thecapability to positively establish an air gap or other effective diaelectric, which together with adequate creepageand clearance distances, will ensure that there is no likely way in which the isolation gap can failelectrically; (b) include, where necessary, means directed at preventing unauthorised interference with orimproper operation of the equipment, for example means of locking off; (c) be located so that the accessibilityand ease with which it may be employed is appropriate for the application. The time and effort which must beexpended to effect isolation should be reasonable having regard to the nature of the equipment and thecircumstances under which isolation may be required, e.g. a very remote means of isolation may be acceptable isisolation is only needed infrequently and any additional time taken to effect isolation does not result indanger; (d) be clearly marked so as to show to which equipment it relates, unless there could be no doubt thatthis would be obvious to any person who may need to operate it; (e) only be common to several items of electricalequipment where it is appropriate for those to be isolated as a group. Selection of isolatorswitches 189 Isolator switches (or disconnectors) will often be employed as the means of effectingdisconnection and secure separation from the supply. In selecting appropriate equipment to perform this functionparticular regards should be given to: (a) the isolating distance between contacts or other means of isolationwhich should be in accordance with an appropriate Standard or be otherwise equally effective; (b) the position ofthe contacts or other means of isolation which should either be externally visible or clearly and reliableindicated. An indication of the isolated position, other than by direct observation of the isolating gap, shouldoccur when the specified isolating distance has been achieved in each pole; (c) provision to enable the preventionof unauthorised, improper or unintentional energisation, e.g. locking –off facilities. N.B. Theseregulations are for guidance only and were correct at time of print. They are subject to update and review.