The PAT Testing Process

The Portable Appliance Testing Process

Reasons For The Tests

The aim here is to explain the fundamental reasons for the tests performed and to offer practical guidance on test procedures. Such guidance can only be given in general terms and practical training is recommended in order to address specific problems. The tests to be performed should reflect the Type Approval tests applicable to the type of unit to be tested. Routine Safety tests should confirm that the original design safety still exists and is of such integrity; that the unit under test is likely to remain safe at the very least until the next scheduled test date. This latter criterion may require the test person to make a prospective judgement.

In-Service Tests

The IEE "Code of Practice for In-Service Inspection and Testing of Electrical Equipment" suggests an in-service test where testing is carried out as a routine to determine whether electrical equipment is in a satisfactory condition. Most companies and organisations that wish to comply with the requirements of the Electricity at Work Regulations 1989 will carry out in-service tests.

Preliminary Visual Inspection

In practice approximately 80% of all equipment defects are found during a preliminary visual inspection. A detailed examination by a competent and conscientious person will make the greatest contribution to hazard elimination.

  1. The exterior of the equipment should be inspected for:
    • Physical damage
    • Signs of overheating.
    • Signs of ingress of liquid or foreign materials.
    Pay particular attention to possible physical damage at accessible mains components such as switches, fuses and appliance couplers.
  2. All mains and power cords, including interconnecting cords should be checked for physical damage. All flexible cords showing any sign of damage should be replaced.
  3. Where re-wireable plugs or appliance couplers are used, their covers should be removed, and
    • Terminations and cord grips should be checked for tightness.
    • Terminations should be checked for correct polarity.
    • Conductors should be checked for damage or loose strands.
    Operator accessible fuses on the outside of the equipment should be checked for correct type and rating. If the equipment manufacturer has specified a particular rating for the plug fuse, this should also be checked. If the manufacturer has not specified a fuse rating for the plug the preferred fuse size is detailed in Table H related to the cross-sectional area of the cord conductors. Ensure that properly manufactured cartridge fuses are used and that fuses have not been replaced with a metal bar, wrapped in metallic foil or similar non standard method.

Classes Of Equipment Construction

The equipment to be tested will normally be constructed in one of three basic classes, designated Class I, II or III. Constructional methods are summarised below, full details can be found in BS2754. Class I equipment will provide the user with two levels of protection. The innermost level is the functional or basic insulation covering live internal parts. The second level of protection is provided by a conductive case which is earthed. This latter level of protection implies that Class I equipment could be a high hazard potential since it relies on the integrity of an electrical connection (the protective conductor or earth). Class II equipment also provides the user with two levels of protection, both levels being provided by insulation. Such equipment is often described as "double insulated" and should carry the symbol o.

The first protective barrier is the functional or basic Insulation while the outer protective layer is known as the supplementary insulation, which may comprise either of an insulating internal lining to a conductive case or in majority of instances, forms the case itself. Class III equipment relies on the supply from a separated extra-low voltage source (SELV) such as an isolating transformer to EN 61558.

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