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School of Physics Safety Manual
> 6. Electrical Safety
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School of Physics Safety Manual
Building and Estates are responsible for carrying out 5 year mandatory periodic electrical testing of all permanent electrical installations. Anyone who carries out live work must receive special trainingin the techniques involved. No one should work on live equipment unaccompanied and live work must be carried out in accordance with approved procedures. Before work commences adequate screening of adjacent live conductors and earthed metal work is imperative. Full use should be made of properly insulated tools, rubber mats and rubber gloves. Low voltage (<250V) and medium voltage (<650V) apparatus should be worked upon with the apparatus dead if practicable. Maintenance of high voltage apparatus must be carried out with the apparatus completely isolated.
Voltages above 50 volts AC and 120 volts DC are hazardous and can be fatal. Fatal accidents have occurred in unfavourable circumstances with only a 40V supply. The hazards arising from the use of electrical apparatus are the risks of electric shock, burns, fire and explosion, injury from involuntary reaction to otherwise harmless shock, and in the microwave and ultraviolet range, radiation damage. If batteries etc are used for low voltage supplies the terminals and connections should be protected to avoid the danger of a short-circuit and hence burns arising from conductors which may accidentally fall on the battery. Electric shock can cause cardiac arrest or cessation of breathing, either of which can be fatal.
Burns can occur externally or internally. External burns can be caused by the passage of an electric current through the skin or as a result of an electric arc or a short circuit. Burns resulting from short circuits are often made worse by pieces of molten metal, from vaporised conductors, embedding in the skin. Internal burns are caused by the passage of electric current through blood vessels and internal organs.
The main causes of such accidents are the use of defective or broken equipment, faulty connections, wrongly sized fuses and the utilisation of wiring of inadequate load bearing capacity. If you are in any doubt concerning any of these features in connection with any electric installation on which you work, you should consult your Supervisor or School Electrical Adviser. Under no circumstances should you use electrical apparatus about which you have any doubt over safety.
It is usual to safeguard against electrical shock by ensuring that external metal casings of all apparatus or equipment is earthed, and so to fasten such a casing or screen that it is impossible to touch any electrically ‘live’ parts of the apparatus. With correctly earthed supply installations, the use of well designed and correctly earthed commercial equipment, the risk of electric shock should be nil. It is important to realise that certain modern items of equipment, particularly power drills are not earthed through the casings, but rely on efficient double insulation. Under no circumstances, therefore, should the eternal casings of these items be interfered with. Items with defective, especially cracked casings, should not be used but returned to a competent electrician for repair.
Electrical equipment which is often moved and which subjects the plug to hard wear e.g. portable electric drills, soldering irons etc should have plugs of the shock resistant type. Do not, for example, allow leads to pass under water baths.
On some equipment of foreign origin the plugs are not fused. If in doubt consult the School Electrical Adviser.
The continuity of earth connections on portable equipment must be checked periodically (see PAT testing). If any normally earthed equipment must be left unearthed for some specific purpose, a notice should be attached which makes this quite evident to any unsuspecting person.
Flexible rubber leaders should be kept away from hot surfaces and where connections have to be made in hot locations the cables should be suitably protected.
Particular care is needed when electrical equipment is used near water. Outlets should be situated as far away as possible from sinks and care should be taken to ensure that water from condenser tubing, water baths etc does not leak onto electrical installations and equipment.
The maintenance of equipment and wiring is a high priority. Any suspected fault should be reported to the School Safety Officer immediately.
Repairs of equipment must only be carried out by the qualified technicians. Faulty equipment should be reported to the School Safety Officer, who will arrange for the repair.
On no account should research workers attempt electrical repairs of any type including the replacement of 13 amp plugs. Any item of electrical equipment which is considered faulty or in need of any minor repair MUST be handed to the technician in charge of the laboratory.
Under the Electricity at Work Regulations 1989 all electrical equipment and appliances used within the School must be tested at recommended intervals. The technician responsible for the laboratory carries this out. A green label will be attached to the equipment stating date of test and when the next test is due. Test frequency is as follows:
Check all equipment that you use has a valid electrical test label before use. The technician responsible for the laboratory should be informed immediately of any equipment that is out of test date. Do not use such equipment.
Any item that has failed the PA test or is faulty should be labelled accordingly and taken out of service immediately.