Portable appliance testing

British law (the Electricity at Work Regulations 1989) requires that all electrical systems (including electrical appliances) are maintained (so far as is reasonably practicable) to prevent danger. Private houses are not covered by this legislation, although occupiers' liability requires householders not to deliberately expose occupants or visitors to unreasonable risks. The HSE and the local authority are responsible for the policing of this legislation.

Guidance from the Institution of Engineering and Technology (IET, published under the IEE brand) and the Health and Safety Executive (HSE) recommends that a competent person must inspect the installation regularly in any public building or a place that people work. They suggest initial intervals for combined inspection and testing that range from three months (for construction equipment) to one year, and in many cases, longer periods for re-testing (certain types of appliance in schools, hotels, offices and shops).[1]

Although the Electricity at Work Regulations 1989 is an obligation on UK businesses, there is no obligation to undertake PAT inspection. In reality neither act nor their corresponding regulations and associated statutory instruments detail PAT inspection as an obligation, but rather impose a requirement of maintenance of safety and evidence of routine maintenance for all hand-held, portable and plug-in equipment.

Today a great many private companies and other organizations do meet their legal obligations to protect their workers by an enforced PAT regime, but it is not the only route.

Recent HSE publications have relaxed their tone somewhat to acknowledge this, and now point out that in many situations annual PAT is disproportionate to the risks and is often not required.[2] In 2011, the HSE reviewed its approach to portable appliance maintenance in its own offices. Thinking about the type of equipment in use, and how it was used, the HSE looked back at the results from its annual testing of portable appliances across its estate over the last five years. Using the results of the previous tests, the HSE decided that further portable appliance tests are not needed within the foreseeable future or at all for certain types of portable equipment. Also, they decided to continue to monitor any faults reported as a result of user checks and visual inspections and review its maintenance system if evidence suggests that it needs revising. Electrical equipment will continue to be maintained by a series of user checks and visual inspections by staff that have had some training.

Annual portable appliance testing is not always necessary in low risk environments. You do not need to be qualified as an electrician to carry out visual inspections. Regular user checks and visual inspections can be a good method of maintaining portable electric equipment. For landlords maintaining legal requirements it is not compulsory for them to have all appliances tested, but they do need to show a "duty of care" and most letting agents recommend that a test certificate is obtained.[3]

Advising the user of potential danger signs can result in problems being picked up before they can result in any danger. For example, if the power cable is frayed or the plug is cracked, users need to be advised not to use the appliance and report the fault to a supervisor. This information can be put across, say by the use of a poster or in a memo. User checks are always carried out before the operation, and the results are generally not recorded unless a defect is identified.

This is a process of simply inspecting the appliance, the cable and the plug for any obvious signs of damage. According to the HSE, this process can find more than 90% of faults.[4]

At periodic intervals, the portable appliances are tested to measure that the degree of protection to ensure that it is adequate. At these intervals, a formal visual inspection is carried out and then followed by electrical testing. Note the inside of the plug should be checked unless it is moulded or there is an unbroken seal covering the screws (bad internal wiring or an unsuitable fuse would cause the item to be classed as dangerous).

This test shows the resistance offered by the earthing rods with the connection leads. Various testing instruments are available for earthing resistance tests. The earthing resistance should be less than 1Ω.

The equipment shall have a measured resistance of the protective earth circuit, or the earthing conductor of an extension cord or appliance cord set, which does not exceed 1Ω.[5]

Testing is performed using an ohmmeter or PAT tester;

• Using the ohmmeter to produce a reading;
• Using 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 choice of which of the tests to use is at the operator's discretion as there is merit in each test for given situations. Later model testers that are battery powered are limited to doing the "screen test". Older mains powered units can do all tests. 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. On the other hand, 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.

A leakage current test performed at rated voltage with values not exceeding 5mA for Class I appliances or 1mA for Class II appliances.[6]

Alternatively, measured insulation resistance (IR[7]) values are not less than 1MΩ for Class I and Class II appliances at 500 V d.c., or at 250 V d.c.[8] to avoid the equipment apparently failing the test because the metal oxide varistors (MOVs) or electro-magnetic interference (EMI) suppression triggered, for equipment containing voltage limiting devices such as MOVs or EMI suppression.

Leakage current testing is performed using a PAT by applying a nominal voltage to the live conductors (active 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 230 V AC. (therefore it can not be performed with a digital multimeter)

Insulation resistance testing is performed using an ohmmeter or portable appliance tester by applying a nominal voltage to the live conductors (active 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 500 V DC (250 V DC may be used for equipment containing MOVs / EMI filtering)

A deficiency of the insulation resistance (500 V /250 V DC) test is that the DC voltage will not activate electromagnetic switches or internal relays etc. that are common in many modern power tools, computers, TVs etc. and therefore it can only test the appliance up to that point. Appliances with these components / design should be tested using the leakage current test.

AS/NZS 3760:2010 section 2.3.3.2 requires a leakage test to be carried out if equipment being tested must be energised to close the circuit or operate a switching device. Leakage testing does require the item being tested to be powered up thus meaning the item will switch on and operate.

In countries where the sockets are polarised, polarity testing is a simple test that can be carried out using a polarity tester to determine whether the active and neutral of the plug end are correctly connected to the corresponding terminals at the socket end.[9][10] Note: The earth is tested during the earth continuity test. In the UK, as per BS 7671, the phase ('Live' or 'Hot') cable should connect with right hand side terminal of the socket (if we face the socket outlet).

• The order (polarity) of the pins of a three pin flat pin plug, to their connections, shall be Earth (radial pin – green/yellow wire), Neutral (light blue wire) and then Active (brown wire), in a clockwise direction, when viewed from the front of the plug looking at the pins.[11]

• The order (polarity) of the socket apertures of a three pin flat pin socket, to their connections, shall be Earth (radial pin – green/yellow wire), Active (brown wire) and then Neutral (light blue wire), in a clockwise direction, when viewed from the front of the socket looking at the apertures.[12]

There are two tests methods to be used;

This test requires specific test equipment RCD tester:

(the TEST button referred to here is the test button on the RCD tester NOT the TEST button on the RCD itself. If the RCD is live, pressing the RCD's own TEST button should ALWAYS trip the RCD).

The RCD tester should be connected with the socket, with earth terminal (must !!) and 1)select the testing range 'delta' (10 mA, 30 mA, 100 mA, 300 mA, 500 mA). 2)Select half delta range, and press TEST button - the RCD should not operate, this ensures against nuisance tripping. 3)Select delta range, and press TEST button - The RCD should operate, within ms for 50 Hz, 230 V system (as per BS 7671)

This test requires specialised test equipment, knowledge and training;

• A current, equal to the rated tripping current, shall be “suddenly” applied between active and protective earth and the operating time measured[13] with maximum trip time 40 ms for Type I and 300 ms for Type II.

In addition to this, many technicians also test;

• using 1/2 (half) the rated tripping current to detect nuisance tripping.
• using 5 times rated tripping current, with trip times reduced accordingly, to simulate high current exposure.
• under 0 degree and 180 degree phases

Best Practice is to test the RCD under 1/2, 1X and 5X rated tripping current, each at both the 0 degree and 180 degree phases.

There are two specific extra checks mandated for microwave ovens in the United Kingdom.

The first is that the device immediately ceases production of the microwave radiation when the door is opened, which checks that the safety interlock systems are functional; and the second is that any leakage when operating is less than 5 mWcm⁻² which indicates that the door and casing are not distorted and any seals are intact so that there is no hazard to those in the vicinity of the equipment.

A piece of calibrated equipment is required for these tests to detect and measure leakage of the 2.4 GHz microwave radiation, it is usually a hand-held device with a sensing antenna that can be scanned over the areas where the door meets the casing to find any radiation hot-spots whilst the unit is operating. As Microwave ovens are not normally designed to be operated without a load this will usually take the form of an open container containing a quantity of water which is used to absorb the energy and as it gets warmed gives an indication that a unit not previously examined by a tester is actually producing microwaves. After checking for leakage the door is required to be opened by whatever means is provided and the measurement device is not to record a level above the given limit. In some scenarios a known quantity of water is heated for a known period of time and the temperature rise over the period of operation is used to generate an indication of the effective power output of the magnetron. This can be helpful to determine whether the oven is operating at the expected power levels indicated by labelling.

These are the simple-to-use and comparatively much cheaper portable appliance testers for most businesses who will test in-house to carry out the testing and suitable for a wide range of businesses. They simply say PASS or FAIL when a test is carried out. Mains powered testers require AC power. Battery operated PAT testers are self-contained and convenient to use. They usually come with rechargeable batteries.

These testers have a simple "lights" system. They have a "Pass" light, a "Fail" light, options for Class I metal / plastic or Class II. They also will show:

• earth continuity
• insulation resistance
• polarity.

These testers display more information than just pass or fail, including:

• Earth continuity resistance (aka Earth Bond) tests with a measurement range of 0 – 1.99 Ω at high test currents (usually 8 A, 10 A or 25 A) and lower test currents (in the range 20 mA to 200 mA), enabling a complete range of appliances including personal computers to be tested;
• Insulation resistance tests at test voltages of 500 V DC or 250 V DC.
• Protective conductor/touch current measurement (sometimes referred to as "earth leakage tests" on some older PAT units);
• Fuse test;
• Lead polarity.

These readings require interpretation by an electrician or someone with electrical understanding. Advanced PAT testers are effective as facilities management tools because they can record the location and test status of electrical equipment and appliances.

Some units can also test Residual-current devices, following the recommendation in the current IEE Code of Practice to test any RCD fitted on an extension lead or multiway adapter.

Modern PAT testers include an RCD test

Some advanced PAT testers can download information to a computer. Bluetooth enabled computerised PAT testers make the two way transfer of test data between the tester and PC-based record keeping systems much simpler, and can be used with other test accessories such as label printers. Records can be maintained using PAT software such as PATorganiser.