Portable Appliance Testing (PAT)

What is PAT - Portable Appliance Testing

Portable appliance testing (PAT) is the term used to describe the examination of electrical appliances and equipment to ensure they are safe to use. Most electrical safety defects can be found by visual examination but some types of defect can only be found by testing. However, it is essential to understand that visual examination is an essential part of the process because some types of electrical safety defect can't be detected by testing alone.

Portable electrical equipment could cause an electric shock or burn, or fire due to damage, wear or misuse. This includes most electrical portable equipment used in all environments, egelectric drills, extension leads, office equipment, portable grinders, pressure water cleaners, floor cleaners, electric kettles and similar equipment used in all environments.

Business equipment (such as computers, printers, photocopiers etc) does not present the same level of risk as other equipment (such as electric drills) providing the leads and plugs are protected from mechanical damage or stress. Movement, and therefore damage through being moved, is less likely to occur, and the equipment is often double insulated and used in a dry, clean environment with non-conducting floors.

Portable electrical equipment should only be used in accordance with the manufacturer’s instructions, for its intended purpose, and in the environment it was designed and constructed for.

What do we Test?

Formal visual inspections

This is a process of simply inspecting the appliance, the cable and the plug for any obvious signs of damage. According to HSE, this process can find more than 90% of faults.

Fuse Rating

The purpose of the fuse within a BS1363 plug is to protect the cable. The correct size of the fuse is ultimately dependant on the current rating of the cable. In most cases we can assume that the manufacturer has fitted the correct size cable and corresponding fuse, in which case the fuse rating recommended by the manufacturer should be used.

The recommended method is to use the 700W rule; for an appliance rated as 700W or less, a 3A fuse should be fitted. For appliances above 700W, a 13A fuse should be fitted.

One complication of using the 700W rule is that some appliances can draw a higher current when they are first switched on, the 700W rule simply won't work. A typical example is a vacuum cleaner that may be rated less than 700W, but will require a 13A fuse to prevent the fuse from blowing when it's first switched on.

BS1363 has a standard of two fuse ratings, 3amp and 13amp. Any fuse rating of up to 13A can still be used, the non standard fuses are available in 1A, 2A, 3A, 5A, 7A and 10A sizes. 5A and 10A fuses are often found in IEC leads connected to IT equipment and do not need to be changed provided they are the appropriate rating for the size of the cable.

The cable and fuse size fitted by the manufacturer can sometimes seem wrong when referring to current cable ratings. A typical example being a modern kettle, when fitted with a 0.75mm² cable, and protected by a 13A fuse. This initially seems incorrect as a 0.75mm² cable is normally rated at just 6A and a kettle can draw nearly 10A. However if the manufacturer has fitted a cable that is less than 2m in length BS1363 can allow a higher current rating and fuse.

Earth resistance test

This test shows the resistance offered by the earthing rods with the connection leads. The earthing resistance should be less than 1Ω

Earth continuity test

The equipment shall have a measured resistance of protective earth circuit, or earthing conductor of an extension cord or appliance cord set, which does not exceed 1Ω. This is tested with a PAT tester under the following conditions:

• 12V maximum, test current range 100mA to 200mA - commonly known as "earth continuity test" or "screen test"
• 12V maximum, test current 10A - commonly known as "routine test"
• 12V maximum, 1.5 times rated current of appliance or 25A, whichever is greater - commonly known as "type test" or "bond test".

The purpose of the high current test is to simulate a fault condition: if a live part contacts the earthed metalwork, the earth conductor should be able to carry sufficient current to blow the fuse and render the appliance safe without the earth conductor itself burning out. Some equipment (especially IT equipment) could be damaged by this test, as the earth connection is only for functional purposes and is not meant to be relied upon for safety.

Insulation resistance test

A leakage current test is performed at rated voltage with values not exceeded 5mA for Class I appliances or 1mA for Class II appliances. Leakage current is tested with a PAT tester by applying nominal voltage to the live conductors (live and neutral) of an appliance, and placing 0 reference on the earthed parts of a Class I appliance or the external metal parts of Class II appliance.

• Nominal voltage is 230V AC

Insulation resistance testing is performed using a portable appliance tester by applying a nominal voltage to the live conductors (live and neutral) of an appliance, and placing 0 volt reference on the earthed parts of a Class I appliance or the external metal parts of a Class II appliance.

• Nominal voltage is 500V DC

Leakage Test

A leakage test will be required out of the equipment must be energised to close the circuit or operate a switching device. Leakage testing requires the item being tested to be powered up, thus meaning the item will switch on and operate.

Polarity Check

The order (polarity) of the connections of a 3-pin plug or extension cord are checked to ensure they are correctly wired Earth (green/yellow), Neutral (light blue), and live (brown), in a clockwise direction when viewed from the front of the plug or socket and looking at the apertures.