In today’s age of advanced scientific and technological advancements, electronic and electrical appliances have become an integral part of any domestic household.
The use of electrical devices and appliances in a typical household is very mainstream nowadays.
These devices include appliances such as microwave ovens, air conditioners, clothing irons, washing machines and dryers, refrigerators, televisions, vacuum cleaners, computers, radiators, hair dryers, hair straighter and curlers, dishwashers and sewing machines etc.
The maintenance and care of these appliances is very important to ensure the safety, risk-free usage and to prevent harm to workers.
Many appliance manufacturers recommend testing at regular intervals to ensure persistent safety.
Portable appliance testing (abbreviated as PAT) is a name of a process through which electrical appliances are routinely checked to ensure that they are safe to use.
Testing involves visual inspection of the equipment and cables, and where required, inspection of grounding (earthing) wires, and a test of the stability of insulation between the current carrying wires and any exposed metal they might be touching.
Most electrical appliances defects can be found through visual examinations but there are some which can only be found through proper testing.
A user who has some basic training or is assisted by the use of a brief checklist can also perform a brief check which can be a very important part of any electrical maintenance regime.
However, a more formal visual check and testing is carried out by a trained and learned professional.
The frequency of this testing depends upon the type of appliance and the environment in which it is used.
There are some appliances which require examination more frequently than others.
One should keep a record of all previous inspections and testing. It can be a useful tool for monitoring and reviewing the effectiveness of the maintenance regime.
The test an appliance undergoes depends on the kind of appliance and its electrical class.
There are various types of tests such as an earth resistance test, earth continuity test; insulation resistance test, polarity check and safety switch tests.
An earth resistance test shows the resistance offered by the earthing rods with the connection leads.
The maximum value of the earthing resistance should be less than 1ohm. In an earth continuity test, the equipment is tested to ensure that the earthing conductor of an extension cord, protective earth circuit or appliance cord set has a measured resistance which does not exceed 1ohm. This test is carried out using an ohmmeter or a PAT tester.
An insulation resistance test is one in which a voltage is applied (particularly a highly controlled, stabilized DC voltage) to measure the amount of current flowing through the dielectric and then a resistance measurement is calculated using Ohm’s Law.
The resistance measurement is in mega ohms and is used to evaluate insulation integrity.
The insulation resistance test can be used as a quality control measure when a piece of electrical equipment is produced, an installation requirement to ensure that specifications and met and to verify proper hookup, to keep a periodic maintenance check and as a troubleshooting tool.
Another type of test carried out during PAT is the polarity test. In places where the sockets are polarized, polarity testing is a simple test that is carried out using a polarity tester to determine whether the active and neutral ends of the plug are correctly connected to the corresponding terminals at the socket end.
While the safety switch test has two methods. One is the press button method and the other is the applied current method.