INTRODUCTION
In the course of testing small domestic appliances there may be some operations carried out with live parts exposed. Equipment so tested may include television sets or other audio-visual equipment and 'white goods'. Safety precautions that should be followed are detailed below.
TESTING ENVIRONMENT
The testing environment should be as earth-free as possible, with a minimum of exposed earthed metalwork. The floors and walls should be insulated and/or covered with an insulating floor covering, benches and other 'furniture' should be made of non-conducting material and it is good practice that the electrical supply is via an isolating transformer. Where it is necessary to have a mains socket outlet connected directly to the supply, it is good practice to install a Residual Current Device (earth trip) in the supply. Individuals carrying out testing should be kept far enough apart so that they cannot touch each other, otherwise two undetected faults on each piece of equipment under test could cause current to flow through both persons. An illustrative diagram of the safety consideration at an electrical testing workstation can be found in booklet HS (G)13 'Electrical Testing'.
TESTING OF AUDIO-VISUAL EQUIPMENT
This equipment can be of Class I or Class II design, or might not be classified as such but housed in an insulating enclosure. A lot of mains-powered equipment only uses mains power to supply what is known as a power supply unit. This is a sub-assembly within the equipment and from this unit onwards to the working parts the voltages are in the category of extra low voltage so that the danger of electric shock is removed. On some equipment the internal metal parts are connected to one pole of the main supply - older designs of TV sets are typical of this type. If the equipment is connected such that the live conductor is connected to the chassis, when a test engineer is working with covers removed and is in an environment where earth leakage paths exist, electric shock risk is high. Consequently an adequately rated isolating transformer should be used, and where there are a number of adjacent working positions individual isolating transformers should be used for each piece of equipment. Further precautions should include a non-conducting work environment (including bench, socket outlets and other service equipment). The use of a 30mS Residual Current Device (RCD) for supplementary protection is also advised.
WHITE GOODS TESTING
There are likely to be many dangerous live conductors exposed if the machines are worked on with the covers removed. The main precaution that should be adopted is to provide insulation or barriers to prevent accidental contact. These protective devices could be of a temporary nature and be fitted before testing commences.
ELECTRICAL TEST EQUIPMENT
Guidance Note GS 38 'Electrical test equipment for use by electricians' provides guidance for electrically competent people involved in electrical testing, diagnosis and repair. The advice includes reference to the following:
Design safety - summarised as follows :
Probes
· minimum of exposed metal
· finger barriers to prevent access to live terminals
· high breaking capacity fuses and/or current limitation
Leads
· robust, flexible and well insulted
· coloured to allow them to be easily distinguished from each other
· shrouded or firmly attached connectors
Illustrative diagrams can be found in GS38.
System of work - before testing begins it is essential to establish that the test device, including all leads, probes and connectors, is suitably rated for the voltages and current's which may be present. The equipment which is to be worked on, must be safe for the intended test and the working environment must not present additional dangers. Appropriate precautions should be taken whilst testing is carried out, as outlined previously. Test devices/equipment should be regularly inspected and, where necessary, tested by a competent person.
HSE electrical inspection and testing webpage
Talking leaflets
These files are provided in mp3 format,
INDG231 Electrical safety and you
Health & safety law: What you should know
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